build: move package sources from src/pkg to src

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.

12 files changed, 3829 insertions, 0 deletions

diff --git a/src/strings/example_test.go b/src/strings/example_test.go
new file mode 100644
index 000000000..7243e16b1
--- /dev/null
+++ b/src/strings/example_test.go
@@ -0,0 +1,225 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings_test
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+)
+
+func ExampleFields() {
+	fmt.Printf("Fields are: %q", strings.Fields("  foo bar  baz   "))
+	// Output: Fields are: ["foo" "bar" "baz"]
+}
+
+func ExampleFieldsFunc() {
+	f := func(c rune) bool {
+		return !unicode.IsLetter(c) && !unicode.IsNumber(c)
+	}
+	fmt.Printf("Fields are: %q", strings.FieldsFunc("  foo1;bar2,baz3...", f))
+	// Output: Fields are: ["foo1" "bar2" "baz3"]
+}
+
+func ExampleContains() {
+	fmt.Println(strings.Contains("seafood", "foo"))
+	fmt.Println(strings.Contains("seafood", "bar"))
+	fmt.Println(strings.Contains("seafood", ""))
+	fmt.Println(strings.Contains("", ""))
+	// Output:
+	// true
+	// false
+	// true
+	// true
+}
+
+func ExampleContainsAny() {
+	fmt.Println(strings.ContainsAny("team", "i"))
+	fmt.Println(strings.ContainsAny("failure", "u & i"))
+	fmt.Println(strings.ContainsAny("foo", ""))
+	fmt.Println(strings.ContainsAny("", ""))
+	// Output:
+	// false
+	// true
+	// false
+	// false
+}
+
+func ExampleCount() {
+	fmt.Println(strings.Count("cheese", "e"))
+	fmt.Println(strings.Count("five", "")) // before & after each rune
+	// Output:
+	// 3
+	// 5
+}
+
+func ExampleEqualFold() {
+	fmt.Println(strings.EqualFold("Go", "go"))
+	// Output: true
+}
+
+func ExampleIndex() {
+	fmt.Println(strings.Index("chicken", "ken"))
+	fmt.Println(strings.Index("chicken", "dmr"))
+	// Output:
+	// 4
+	// -1
+}
+
+func ExampleIndexFunc() {
+	f := func(c rune) bool {
+		return unicode.Is(unicode.Han, c)
+	}
+	fmt.Println(strings.IndexFunc("Hello, 世界", f))
+	fmt.Println(strings.IndexFunc("Hello, world", f))
+	// Output:
+	// 7
+	// -1
+}
+
+func ExampleIndexAny() {
+	fmt.Println(strings.IndexAny("chicken", "aeiouy"))
+	fmt.Println(strings.IndexAny("crwth", "aeiouy"))
+	// Output:
+	// 2
+	// -1
+}
+
+func ExampleIndexRune() {
+	fmt.Println(strings.IndexRune("chicken", 'k'))
+	fmt.Println(strings.IndexRune("chicken", 'd'))
+	// Output:
+	// 4
+	// -1
+}
+
+func ExampleLastIndex() {
+	fmt.Println(strings.Index("go gopher", "go"))
+	fmt.Println(strings.LastIndex("go gopher", "go"))
+	fmt.Println(strings.LastIndex("go gopher", "rodent"))
+	// Output:
+	// 0
+	// 3
+	// -1
+}
+
+func ExampleJoin() {
+	s := []string{"foo", "bar", "baz"}
+	fmt.Println(strings.Join(s, ", "))
+	// Output: foo, bar, baz
+}
+
+func ExampleRepeat() {
+	fmt.Println("ba" + strings.Repeat("na", 2))
+	// Output: banana
+}
+
+func ExampleReplace() {
+	fmt.Println(strings.Replace("oink oink oink", "k", "ky", 2))
+	fmt.Println(strings.Replace("oink oink oink", "oink", "moo", -1))
+	// Output:
+	// oinky oinky oink
+	// moo moo moo
+}
+
+func ExampleSplit() {
+	fmt.Printf("%q\n", strings.Split("a,b,c", ","))
+	fmt.Printf("%q\n", strings.Split("a man a plan a canal panama", "a "))
+	fmt.Printf("%q\n", strings.Split(" xyz ", ""))
+	fmt.Printf("%q\n", strings.Split("", "Bernardo O'Higgins"))
+	// Output:
+	// ["a" "b" "c"]
+	// ["" "man " "plan " "canal panama"]
+	// [" " "x" "y" "z" " "]
+	// [""]
+}
+
+func ExampleSplitN() {
+	fmt.Printf("%q\n", strings.SplitN("a,b,c", ",", 2))
+	z := strings.SplitN("a,b,c", ",", 0)
+	fmt.Printf("%q (nil = %v)\n", z, z == nil)
+	// Output:
+	// ["a" "b,c"]
+	// [] (nil = true)
+}
+
+func ExampleSplitAfter() {
+	fmt.Printf("%q\n", strings.SplitAfter("a,b,c", ","))
+	// Output: ["a," "b," "c"]
+}
+
+func ExampleSplitAfterN() {
+	fmt.Printf("%q\n", strings.SplitAfterN("a,b,c", ",", 2))
+	// Output: ["a," "b,c"]
+}
+
+func ExampleTitle() {
+	fmt.Println(strings.Title("her royal highness"))
+	// Output: Her Royal Highness
+}
+
+func ExampleToTitle() {
+	fmt.Println(strings.ToTitle("loud noises"))
+	fmt.Println(strings.ToTitle("хлеб"))
+	// Output:
+	// LOUD NOISES
+	// ХЛЕБ
+}
+
+func ExampleTrim() {
+	fmt.Printf("[%q]", strings.Trim(" !!! Achtung! Achtung! !!! ", "! "))
+	// Output: ["Achtung! Achtung"]
+}
+
+func ExampleMap() {
+	rot13 := func(r rune) rune {
+		switch {
+		case r >= 'A' && r <= 'Z':
+			return 'A' + (r-'A'+13)%26
+		case r >= 'a' && r <= 'z':
+			return 'a' + (r-'a'+13)%26
+		}
+		return r
+	}
+	fmt.Println(strings.Map(rot13, "'Twas brillig and the slithy gopher..."))
+	// Output: 'Gjnf oevyyvt naq gur fyvgul tbcure...
+}
+
+func ExampleTrimSpace() {
+	fmt.Println(strings.TrimSpace(" \t\n a lone gopher \n\t\r\n"))
+	// Output: a lone gopher
+}
+
+func ExampleNewReplacer() {
+	r := strings.NewReplacer("<", "&lt;", ">", "&gt;")
+	fmt.Println(r.Replace("This is <b>HTML</b>!"))
+	// Output: This is &lt;b&gt;HTML&lt;/b&gt;!
+}
+
+func ExampleToUpper() {
+	fmt.Println(strings.ToUpper("Gopher"))
+	// Output: GOPHER
+}
+
+func ExampleToLower() {
+	fmt.Println(strings.ToLower("Gopher"))
+	// Output: gopher
+}
+
+func ExampleTrimSuffix() {
+	var s = "Hello, goodbye, etc!"
+	s = strings.TrimSuffix(s, "goodbye, etc!")
+	s = strings.TrimSuffix(s, "planet")
+	fmt.Print(s, "world!")
+	// Output: Hello, world!
+}
+
+func ExampleTrimPrefix() {
+	var s = "Goodbye,, world!"
+	s = strings.TrimPrefix(s, "Goodbye,")
+	s = strings.TrimPrefix(s, "Howdy,")
+	fmt.Print("Hello" + s)
+	// Output: Hello, world!
+}
diff --git a/src/strings/export_test.go b/src/strings/export_test.go
new file mode 100644
index 000000000..17c806aa5
--- /dev/null
+++ b/src/strings/export_test.go
@@ -0,0 +1,45 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings
+
+func (r *Replacer) Replacer() interface{} {
+	return r.r
+}
+
+func (r *Replacer) PrintTrie() string {
+	gen := r.r.(*genericReplacer)
+	return gen.printNode(&gen.root, 0)
+}
+
+func (r *genericReplacer) printNode(t *trieNode, depth int) (s string) {
+	if t.priority > 0 {
+		s += "+"
+	} else {
+		s += "-"
+	}
+	s += "\n"
+
+	if t.prefix != "" {
+		s += Repeat(".", depth) + t.prefix
+		s += r.printNode(t.next, depth+len(t.prefix))
+	} else if t.table != nil {
+		for b, m := range r.mapping {
+			if int(m) != r.tableSize && t.table[m] != nil {
+				s += Repeat(".", depth) + string([]byte{byte(b)})
+				s += r.printNode(t.table[m], depth+1)
+			}
+		}
+	}
+	return
+}
+
+func StringFind(pattern, text string) int {
+	return makeStringFinder(pattern).next(text)
+}
+
+func DumpTables(pattern string) ([]int, []int) {
+	finder := makeStringFinder(pattern)
+	return finder.badCharSkip[:], finder.goodSuffixSkip
+}
diff --git a/src/strings/reader.go b/src/strings/reader.go
new file mode 100644
index 000000000..82df97439
--- /dev/null
+++ b/src/strings/reader.go
@@ -0,0 +1,144 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings
+
+import (
+	"errors"
+	"io"
+	"unicode/utf8"
+)
+
+// A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo,
+// io.ByteScanner, and io.RuneScanner interfaces by reading
+// from a string.
+type Reader struct {
+	s        string
+	i        int64 // current reading index
+	prevRune int   // index of previous rune; or < 0
+}
+
+// Len returns the number of bytes of the unread portion of the
+// string.
+func (r *Reader) Len() int {
+	if r.i >= int64(len(r.s)) {
+		return 0
+	}
+	return int(int64(len(r.s)) - r.i)
+}
+
+func (r *Reader) Read(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	if r.i >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	r.prevRune = -1
+	n = copy(b, r.s[r.i:])
+	r.i += int64(n)
+	return
+}
+
+func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
+	// cannot modify state - see io.ReaderAt
+	if off < 0 {
+		return 0, errors.New("strings.Reader.ReadAt: negative offset")
+	}
+	if off >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	n = copy(b, r.s[off:])
+	if n < len(b) {
+		err = io.EOF
+	}
+	return
+}
+
+func (r *Reader) ReadByte() (b byte, err error) {
+	r.prevRune = -1
+	if r.i >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	b = r.s[r.i]
+	r.i++
+	return
+}
+
+func (r *Reader) UnreadByte() error {
+	r.prevRune = -1
+	if r.i <= 0 {
+		return errors.New("strings.Reader.UnreadByte: at beginning of string")
+	}
+	r.i--
+	return nil
+}
+
+func (r *Reader) ReadRune() (ch rune, size int, err error) {
+	if r.i >= int64(len(r.s)) {
+		r.prevRune = -1
+		return 0, 0, io.EOF
+	}
+	r.prevRune = int(r.i)
+	if c := r.s[r.i]; c < utf8.RuneSelf {
+		r.i++
+		return rune(c), 1, nil
+	}
+	ch, size = utf8.DecodeRuneInString(r.s[r.i:])
+	r.i += int64(size)
+	return
+}
+
+func (r *Reader) UnreadRune() error {
+	if r.prevRune < 0 {
+		return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune")
+	}
+	r.i = int64(r.prevRune)
+	r.prevRune = -1
+	return nil
+}
+
+// Seek implements the io.Seeker interface.
+func (r *Reader) Seek(offset int64, whence int) (int64, error) {
+	r.prevRune = -1
+	var abs int64
+	switch whence {
+	case 0:
+		abs = offset
+	case 1:
+		abs = int64(r.i) + offset
+	case 2:
+		abs = int64(len(r.s)) + offset
+	default:
+		return 0, errors.New("strings.Reader.Seek: invalid whence")
+	}
+	if abs < 0 {
+		return 0, errors.New("strings.Reader.Seek: negative position")
+	}
+	r.i = abs
+	return abs, nil
+}
+
+// WriteTo implements the io.WriterTo interface.
+func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
+	r.prevRune = -1
+	if r.i >= int64(len(r.s)) {
+		return 0, nil
+	}
+	s := r.s[r.i:]
+	m, err := io.WriteString(w, s)
+	if m > len(s) {
+		panic("strings.Reader.WriteTo: invalid WriteString count")
+	}
+	r.i += int64(m)
+	n = int64(m)
+	if m != len(s) && err == nil {
+		err = io.ErrShortWrite
+	}
+	return
+}
+
+// NewReader returns a new Reader reading from s.
+// It is similar to bytes.NewBufferString but more efficient and read-only.
+func NewReader(s string) *Reader { return &Reader{s, 0, -1} }
diff --git a/src/strings/reader_test.go b/src/strings/reader_test.go
new file mode 100644
index 000000000..bee90eb25
--- /dev/null
+++ b/src/strings/reader_test.go
@@ -0,0 +1,159 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings_test
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"sync"
+	"testing"
+)
+
+func TestReader(t *testing.T) {
+	r := strings.NewReader("0123456789")
+	tests := []struct {
+		off     int64
+		seek    int
+		n       int
+		want    string
+		wantpos int64
+		seekerr string
+	}{
+		{seek: os.SEEK_SET, off: 0, n: 20, want: "0123456789"},
+		{seek: os.SEEK_SET, off: 1, n: 1, want: "1"},
+		{seek: os.SEEK_CUR, off: 1, wantpos: 3, n: 2, want: "34"},
+		{seek: os.SEEK_SET, off: -1, seekerr: "strings.Reader.Seek: negative position"},
+		{seek: os.SEEK_SET, off: 1 << 33, wantpos: 1 << 33},
+		{seek: os.SEEK_CUR, off: 1, wantpos: 1<<33 + 1},
+		{seek: os.SEEK_SET, n: 5, want: "01234"},
+		{seek: os.SEEK_CUR, n: 5, want: "56789"},
+		{seek: os.SEEK_END, off: -1, n: 1, wantpos: 9, want: "9"},
+	}
+
+	for i, tt := range tests {
+		pos, err := r.Seek(tt.off, tt.seek)
+		if err == nil && tt.seekerr != "" {
+			t.Errorf("%d. want seek error %q", i, tt.seekerr)
+			continue
+		}
+		if err != nil && err.Error() != tt.seekerr {
+			t.Errorf("%d. seek error = %q; want %q", i, err.Error(), tt.seekerr)
+			continue
+		}
+		if tt.wantpos != 0 && tt.wantpos != pos {
+			t.Errorf("%d. pos = %d, want %d", i, pos, tt.wantpos)
+		}
+		buf := make([]byte, tt.n)
+		n, err := r.Read(buf)
+		if err != nil {
+			t.Errorf("%d. read = %v", i, err)
+			continue
+		}
+		got := string(buf[:n])
+		if got != tt.want {
+			t.Errorf("%d. got %q; want %q", i, got, tt.want)
+		}
+	}
+}
+
+func TestReadAfterBigSeek(t *testing.T) {
+	r := strings.NewReader("0123456789")
+	if _, err := r.Seek(1<<31+5, os.SEEK_SET); err != nil {
+		t.Fatal(err)
+	}
+	if n, err := r.Read(make([]byte, 10)); n != 0 || err != io.EOF {
+		t.Errorf("Read = %d, %v; want 0, EOF", n, err)
+	}
+}
+
+func TestReaderAt(t *testing.T) {
+	r := strings.NewReader("0123456789")
+	tests := []struct {
+		off     int64
+		n       int
+		want    string
+		wanterr interface{}
+	}{
+		{0, 10, "0123456789", nil},
+		{1, 10, "123456789", io.EOF},
+		{1, 9, "123456789", nil},
+		{11, 10, "", io.EOF},
+		{0, 0, "", nil},
+		{-1, 0, "", "strings.Reader.ReadAt: negative offset"},
+	}
+	for i, tt := range tests {
+		b := make([]byte, tt.n)
+		rn, err := r.ReadAt(b, tt.off)
+		got := string(b[:rn])
+		if got != tt.want {
+			t.Errorf("%d. got %q; want %q", i, got, tt.want)
+		}
+		if fmt.Sprintf("%v", err) != fmt.Sprintf("%v", tt.wanterr) {
+			t.Errorf("%d. got error = %v; want %v", i, err, tt.wanterr)
+		}
+	}
+}
+
+func TestReaderAtConcurrent(t *testing.T) {
+	// Test for the race detector, to verify ReadAt doesn't mutate
+	// any state.
+	r := strings.NewReader("0123456789")
+	var wg sync.WaitGroup
+	for i := 0; i < 5; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			var buf [1]byte
+			r.ReadAt(buf[:], int64(i))
+		}(i)
+	}
+	wg.Wait()
+}
+
+func TestEmptyReaderConcurrent(t *testing.T) {
+	// Test for the race detector, to verify a Read that doesn't yield any bytes
+	// is okay to use from multiple goroutines. This was our historic behavior.
+	// See golang.org/issue/7856
+	r := strings.NewReader("")
+	var wg sync.WaitGroup
+	for i := 0; i < 5; i++ {
+		wg.Add(2)
+		go func() {
+			defer wg.Done()
+			var buf [1]byte
+			r.Read(buf[:])
+		}()
+		go func() {
+			defer wg.Done()
+			r.Read(nil)
+		}()
+	}
+	wg.Wait()
+}
+
+func TestWriteTo(t *testing.T) {
+	const str = "0123456789"
+	for i := 0; i <= len(str); i++ {
+		s := str[i:]
+		r := strings.NewReader(s)
+		var b bytes.Buffer
+		n, err := r.WriteTo(&b)
+		if expect := int64(len(s)); n != expect {
+			t.Errorf("got %v; want %v", n, expect)
+		}
+		if err != nil {
+			t.Errorf("for length %d: got error = %v; want nil", len(s), err)
+		}
+		if b.String() != s {
+			t.Errorf("got string %q; want %q", b.String(), s)
+		}
+		if r.Len() != 0 {
+			t.Errorf("reader contains %v bytes; want 0", r.Len())
+		}
+	}
+}
diff --git a/src/strings/replace.go b/src/strings/replace.go
new file mode 100644
index 000000000..4752641be
--- /dev/null
+++ b/src/strings/replace.go
@@ -0,0 +1,518 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings
+
+import "io"
+
+// Replacer replaces a list of strings with replacements.
+// It is safe for concurrent use by multiple goroutines.
+type Replacer struct {
+	r replacer
+}
+
+// replacer is the interface that a replacement algorithm needs to implement.
+type replacer interface {
+	Replace(s string) string
+	WriteString(w io.Writer, s string) (n int, err error)
+}
+
+// NewReplacer returns a new Replacer from a list of old, new string pairs.
+// Replacements are performed in order, without overlapping matches.
+func NewReplacer(oldnew ...string) *Replacer {
+	if len(oldnew)%2 == 1 {
+		panic("strings.NewReplacer: odd argument count")
+	}
+
+	if len(oldnew) == 2 && len(oldnew[0]) > 1 {
+		return &Replacer{r: makeSingleStringReplacer(oldnew[0], oldnew[1])}
+	}
+
+	allNewBytes := true
+	for i := 0; i < len(oldnew); i += 2 {
+		if len(oldnew[i]) != 1 {
+			return &Replacer{r: makeGenericReplacer(oldnew)}
+		}
+		if len(oldnew[i+1]) != 1 {
+			allNewBytes = false
+		}
+	}
+
+	if allNewBytes {
+		r := byteReplacer{}
+		for i := range r {
+			r[i] = byte(i)
+		}
+		// The first occurrence of old->new map takes precedence
+		// over the others with the same old string.
+		for i := len(oldnew) - 2; i >= 0; i -= 2 {
+			o := oldnew[i][0]
+			n := oldnew[i+1][0]
+			r[o] = n
+		}
+		return &Replacer{r: &r}
+	}
+
+	r := byteStringReplacer{}
+	// The first occurrence of old->new map takes precedence
+	// over the others with the same old string.
+	for i := len(oldnew) - 2; i >= 0; i -= 2 {
+		o := oldnew[i][0]
+		n := oldnew[i+1]
+		r[o] = []byte(n)
+	}
+	return &Replacer{r: &r}
+}
+
+// Replace returns a copy of s with all replacements performed.
+func (r *Replacer) Replace(s string) string {
+	return r.r.Replace(s)
+}
+
+// WriteString writes s to w with all replacements performed.
+func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error) {
+	return r.r.WriteString(w, s)
+}
+
+// trieNode is a node in a lookup trie for prioritized key/value pairs. Keys
+// and values may be empty. For example, the trie containing keys "ax", "ay",
+// "bcbc", "x" and "xy" could have eight nodes:
+//
+//  n0  -
+//  n1  a-
+//  n2  .x+
+//  n3  .y+
+//  n4  b-
+//  n5  .cbc+
+//  n6  x+
+//  n7  .y+
+//
+// n0 is the root node, and its children are n1, n4 and n6; n1's children are
+// n2 and n3; n4's child is n5; n6's child is n7. Nodes n0, n1 and n4 (marked
+// with a trailing "-") are partial keys, and nodes n2, n3, n5, n6 and n7
+// (marked with a trailing "+") are complete keys.
+type trieNode struct {
+	// value is the value of the trie node's key/value pair. It is empty if
+	// this node is not a complete key.
+	value string
+	// priority is the priority (higher is more important) of the trie node's
+	// key/value pair; keys are not necessarily matched shortest- or longest-
+	// first. Priority is positive if this node is a complete key, and zero
+	// otherwise. In the example above, positive/zero priorities are marked
+	// with a trailing "+" or "-".
+	priority int
+
+	// A trie node may have zero, one or more child nodes:
+	//  * if the remaining fields are zero, there are no children.
+	//  * if prefix and next are non-zero, there is one child in next.
+	//  * if table is non-zero, it defines all the children.
+	//
+	// Prefixes are preferred over tables when there is one child, but the
+	// root node always uses a table for lookup efficiency.
+
+	// prefix is the difference in keys between this trie node and the next.
+	// In the example above, node n4 has prefix "cbc" and n4's next node is n5.
+	// Node n5 has no children and so has zero prefix, next and table fields.
+	prefix string
+	next   *trieNode
+
+	// table is a lookup table indexed by the next byte in the key, after
+	// remapping that byte through genericReplacer.mapping to create a dense
+	// index. In the example above, the keys only use 'a', 'b', 'c', 'x' and
+	// 'y', which remap to 0, 1, 2, 3 and 4. All other bytes remap to 5, and
+	// genericReplacer.tableSize will be 5. Node n0's table will be
+	// []*trieNode{ 0:n1, 1:n4, 3:n6 }, where the 0, 1 and 3 are the remapped
+	// 'a', 'b' and 'x'.
+	table []*trieNode
+}
+
+func (t *trieNode) add(key, val string, priority int, r *genericReplacer) {
+	if key == "" {
+		if t.priority == 0 {
+			t.value = val
+			t.priority = priority
+		}
+		return
+	}
+
+	if t.prefix != "" {
+		// Need to split the prefix among multiple nodes.
+		var n int // length of the longest common prefix
+		for ; n < len(t.prefix) && n < len(key); n++ {
+			if t.prefix[n] != key[n] {
+				break
+			}
+		}
+		if n == len(t.prefix) {
+			t.next.add(key[n:], val, priority, r)
+		} else if n == 0 {
+			// First byte differs, start a new lookup table here. Looking up
+			// what is currently t.prefix[0] will lead to prefixNode, and
+			// looking up key[0] will lead to keyNode.
+			var prefixNode *trieNode
+			if len(t.prefix) == 1 {
+				prefixNode = t.next
+			} else {
+				prefixNode = &trieNode{
+					prefix: t.prefix[1:],
+					next:   t.next,
+				}
+			}
+			keyNode := new(trieNode)
+			t.table = make([]*trieNode, r.tableSize)
+			t.table[r.mapping[t.prefix[0]]] = prefixNode
+			t.table[r.mapping[key[0]]] = keyNode
+			t.prefix = ""
+			t.next = nil
+			keyNode.add(key[1:], val, priority, r)
+		} else {
+			// Insert new node after the common section of the prefix.
+			next := &trieNode{
+				prefix: t.prefix[n:],
+				next:   t.next,
+			}
+			t.prefix = t.prefix[:n]
+			t.next = next
+			next.add(key[n:], val, priority, r)
+		}
+	} else if t.table != nil {
+		// Insert into existing table.
+		m := r.mapping[key[0]]
+		if t.table[m] == nil {
+			t.table[m] = new(trieNode)
+		}
+		t.table[m].add(key[1:], val, priority, r)
+	} else {
+		t.prefix = key
+		t.next = new(trieNode)
+		t.next.add("", val, priority, r)
+	}
+}
+
+func (r *genericReplacer) lookup(s string, ignoreRoot bool) (val string, keylen int, found bool) {
+	// Iterate down the trie to the end, and grab the value and keylen with
+	// the highest priority.
+	bestPriority := 0
+	node := &r.root
+	n := 0
+	for node != nil {
+		if node.priority > bestPriority && !(ignoreRoot && node == &r.root) {
+			bestPriority = node.priority
+			val = node.value
+			keylen = n
+			found = true
+		}
+
+		if s == "" {
+			break
+		}
+		if node.table != nil {
+			index := r.mapping[s[0]]
+			if int(index) == r.tableSize {
+				break
+			}
+			node = node.table[index]
+			s = s[1:]
+			n++
+		} else if node.prefix != "" && HasPrefix(s, node.prefix) {
+			n += len(node.prefix)
+			s = s[len(node.prefix):]
+			node = node.next
+		} else {
+			break
+		}
+	}
+	return
+}
+
+// genericReplacer is the fully generic algorithm.
+// It's used as a fallback when nothing faster can be used.
+type genericReplacer struct {
+	root trieNode
+	// tableSize is the size of a trie node's lookup table. It is the number
+	// of unique key bytes.
+	tableSize int
+	// mapping maps from key bytes to a dense index for trieNode.table.
+	mapping [256]byte
+}
+
+func makeGenericReplacer(oldnew []string) *genericReplacer {
+	r := new(genericReplacer)
+	// Find each byte used, then assign them each an index.
+	for i := 0; i < len(oldnew); i += 2 {
+		key := oldnew[i]
+		for j := 0; j < len(key); j++ {
+			r.mapping[key[j]] = 1
+		}
+	}
+
+	for _, b := range r.mapping {
+		r.tableSize += int(b)
+	}
+
+	var index byte
+	for i, b := range r.mapping {
+		if b == 0 {
+			r.mapping[i] = byte(r.tableSize)
+		} else {
+			r.mapping[i] = index
+			index++
+		}
+	}
+	// Ensure root node uses a lookup table (for performance).
+	r.root.table = make([]*trieNode, r.tableSize)
+
+	for i := 0; i < len(oldnew); i += 2 {
+		r.root.add(oldnew[i], oldnew[i+1], len(oldnew)-i, r)
+	}
+	return r
+}
+
+type appendSliceWriter []byte
+
+// Write writes to the buffer to satisfy io.Writer.
+func (w *appendSliceWriter) Write(p []byte) (int, error) {
+	*w = append(*w, p...)
+	return len(p), nil
+}
+
+// WriteString writes to the buffer without string->[]byte->string allocations.
+func (w *appendSliceWriter) WriteString(s string) (int, error) {
+	*w = append(*w, s...)
+	return len(s), nil
+}
+
+type stringWriterIface interface {
+	WriteString(string) (int, error)
+}
+
+type stringWriter struct {
+	w io.Writer
+}
+
+func (w stringWriter) WriteString(s string) (int, error) {
+	return w.w.Write([]byte(s))
+}
+
+func getStringWriter(w io.Writer) stringWriterIface {
+	sw, ok := w.(stringWriterIface)
+	if !ok {
+		sw = stringWriter{w}
+	}
+	return sw
+}
+
+func (r *genericReplacer) Replace(s string) string {
+	buf := make(appendSliceWriter, 0, len(s))
+	r.WriteString(&buf, s)
+	return string(buf)
+}
+
+func (r *genericReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	sw := getStringWriter(w)
+	var last, wn int
+	var prevMatchEmpty bool
+	for i := 0; i <= len(s); {
+		// Fast path: s[i] is not a prefix of any pattern.
+		if i != len(s) && r.root.priority == 0 {
+			index := int(r.mapping[s[i]])
+			if index == r.tableSize || r.root.table[index] == nil {
+				i++
+				continue
+			}
+		}
+
+		// Ignore the empty match iff the previous loop found the empty match.
+		val, keylen, match := r.lookup(s[i:], prevMatchEmpty)
+		prevMatchEmpty = match && keylen == 0
+		if match {
+			wn, err = sw.WriteString(s[last:i])
+			n += wn
+			if err != nil {
+				return
+			}
+			wn, err = sw.WriteString(val)
+			n += wn
+			if err != nil {
+				return
+			}
+			i += keylen
+			last = i
+			continue
+		}
+		i++
+	}
+	if last != len(s) {
+		wn, err = sw.WriteString(s[last:])
+		n += wn
+	}
+	return
+}
+
+// singleStringReplacer is the implementation that's used when there is only
+// one string to replace (and that string has more than one byte).
+type singleStringReplacer struct {
+	finder *stringFinder
+	// value is the new string that replaces that pattern when it's found.
+	value string
+}
+
+func makeSingleStringReplacer(pattern string, value string) *singleStringReplacer {
+	return &singleStringReplacer{finder: makeStringFinder(pattern), value: value}
+}
+
+func (r *singleStringReplacer) Replace(s string) string {
+	var buf []byte
+	i, matched := 0, false
+	for {
+		match := r.finder.next(s[i:])
+		if match == -1 {
+			break
+		}
+		matched = true
+		buf = append(buf, s[i:i+match]...)
+		buf = append(buf, r.value...)
+		i += match + len(r.finder.pattern)
+	}
+	if !matched {
+		return s
+	}
+	buf = append(buf, s[i:]...)
+	return string(buf)
+}
+
+func (r *singleStringReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	sw := getStringWriter(w)
+	var i, wn int
+	for {
+		match := r.finder.next(s[i:])
+		if match == -1 {
+			break
+		}
+		wn, err = sw.WriteString(s[i : i+match])
+		n += wn
+		if err != nil {
+			return
+		}
+		wn, err = sw.WriteString(r.value)
+		n += wn
+		if err != nil {
+			return
+		}
+		i += match + len(r.finder.pattern)
+	}
+	wn, err = sw.WriteString(s[i:])
+	n += wn
+	return
+}
+
+// byteReplacer is the implementation that's used when all the "old"
+// and "new" values are single ASCII bytes.
+// The array contains replacement bytes indexed by old byte.
+type byteReplacer [256]byte
+
+func (r *byteReplacer) Replace(s string) string {
+	var buf []byte // lazily allocated
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r[b] != b {
+			if buf == nil {
+				buf = []byte(s)
+			}
+			buf[i] = r[b]
+		}
+	}
+	if buf == nil {
+		return s
+	}
+	return string(buf)
+}
+
+func (r *byteReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	// TODO(bradfitz): use io.WriteString with slices of s, avoiding allocation.
+	bufsize := 32 << 10
+	if len(s) < bufsize {
+		bufsize = len(s)
+	}
+	buf := make([]byte, bufsize)
+
+	for len(s) > 0 {
+		ncopy := copy(buf, s[:])
+		s = s[ncopy:]
+		for i, b := range buf[:ncopy] {
+			buf[i] = r[b]
+		}
+		wn, err := w.Write(buf[:ncopy])
+		n += wn
+		if err != nil {
+			return n, err
+		}
+	}
+	return n, nil
+}
+
+// byteStringReplacer is the implementation that's used when all the
+// "old" values are single ASCII bytes but the "new" values vary in size.
+// The array contains replacement byte slices indexed by old byte.
+// A nil []byte means that the old byte should not be replaced.
+type byteStringReplacer [256][]byte
+
+func (r *byteStringReplacer) Replace(s string) string {
+	newSize := len(s)
+	anyChanges := false
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r[b] != nil {
+			anyChanges = true
+			// The -1 is because we are replacing 1 byte with len(r[b]) bytes.
+			newSize += len(r[b]) - 1
+		}
+	}
+	if !anyChanges {
+		return s
+	}
+	buf := make([]byte, newSize)
+	bi := buf
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r[b] != nil {
+			n := copy(bi, r[b])
+			bi = bi[n:]
+		} else {
+			bi[0] = b
+			bi = bi[1:]
+		}
+	}
+	return string(buf)
+}
+
+func (r *byteStringReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	sw := getStringWriter(w)
+	last := 0
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r[b] == nil {
+			continue
+		}
+		if last != i {
+			nw, err := sw.WriteString(s[last:i])
+			n += nw
+			if err != nil {
+				return n, err
+			}
+		}
+		last = i + 1
+		nw, err := w.Write(r[b])
+		n += nw
+		if err != nil {
+			return n, err
+		}
+	}
+	if last != len(s) {
+		var nw int
+		nw, err = sw.WriteString(s[last:])
+		n += nw
+	}
+	return
+}
diff --git a/src/strings/replace_test.go b/src/strings/replace_test.go
new file mode 100644
index 000000000..77e48b988
--- /dev/null
+++ b/src/strings/replace_test.go
@@ -0,0 +1,542 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings_test
+
+import (
+	"bytes"
+	"fmt"
+	. "strings"
+	"testing"
+)
+
+var htmlEscaper = NewReplacer(
+	"&", "&amp;",
+	"<", "&lt;",
+	">", "&gt;",
+	`"`, "&quot;",
+	"'", "&apos;",
+)
+
+var htmlUnescaper = NewReplacer(
+	"&amp;", "&",
+	"&lt;", "<",
+	"&gt;", ">",
+	"&quot;", `"`,
+	"&apos;", "'",
+)
+
+// The http package's old HTML escaping function.
+func oldHTMLEscape(s string) string {
+	s = Replace(s, "&", "&amp;", -1)
+	s = Replace(s, "<", "&lt;", -1)
+	s = Replace(s, ">", "&gt;", -1)
+	s = Replace(s, `"`, "&quot;", -1)
+	s = Replace(s, "'", "&apos;", -1)
+	return s
+}
+
+var capitalLetters = NewReplacer("a", "A", "b", "B")
+
+// TestReplacer tests the replacer implementations.
+func TestReplacer(t *testing.T) {
+	type testCase struct {
+		r       *Replacer
+		in, out string
+	}
+	var testCases []testCase
+
+	// str converts 0xff to "\xff". This isn't just string(b) since that converts to UTF-8.
+	str := func(b byte) string {
+		return string([]byte{b})
+	}
+	var s []string
+
+	// inc maps "\x00"->"\x01", ..., "a"->"b", "b"->"c", ..., "\xff"->"\x00".
+	s = nil
+	for i := 0; i < 256; i++ {
+		s = append(s, str(byte(i)), str(byte(i+1)))
+	}
+	inc := NewReplacer(s...)
+
+	// Test cases with 1-byte old strings, 1-byte new strings.
+	testCases = append(testCases,
+		testCase{capitalLetters, "brad", "BrAd"},
+		testCase{capitalLetters, Repeat("a", (32<<10)+123), Repeat("A", (32<<10)+123)},
+		testCase{capitalLetters, "", ""},
+
+		testCase{inc, "brad", "csbe"},
+		testCase{inc, "\x00\xff", "\x01\x00"},
+		testCase{inc, "", ""},
+
+		testCase{NewReplacer("a", "1", "a", "2"), "brad", "br1d"},
+	)
+
+	// repeat maps "a"->"a", "b"->"bb", "c"->"ccc", ...
+	s = nil
+	for i := 0; i < 256; i++ {
+		n := i + 1 - 'a'
+		if n < 1 {
+			n = 1
+		}
+		s = append(s, str(byte(i)), Repeat(str(byte(i)), n))
+	}
+	repeat := NewReplacer(s...)
+
+	// Test cases with 1-byte old strings, variable length new strings.
+	testCases = append(testCases,
+		testCase{htmlEscaper, "No changes", "No changes"},
+		testCase{htmlEscaper, "I <3 escaping & stuff", "I &lt;3 escaping &amp; stuff"},
+		testCase{htmlEscaper, "&&&", "&amp;&amp;&amp;"},
+		testCase{htmlEscaper, "", ""},
+
+		testCase{repeat, "brad", "bbrrrrrrrrrrrrrrrrrradddd"},
+		testCase{repeat, "abba", "abbbba"},
+		testCase{repeat, "", ""},
+
+		testCase{NewReplacer("a", "11", "a", "22"), "brad", "br11d"},
+	)
+
+	// The remaining test cases have variable length old strings.
+
+	testCases = append(testCases,
+		testCase{htmlUnescaper, "&amp;amp;", "&amp;"},
+		testCase{htmlUnescaper, "&lt;b&gt;HTML&apos;s neat&lt;/b&gt;", "<b>HTML's neat</b>"},
+		testCase{htmlUnescaper, "", ""},
+
+		testCase{NewReplacer("a", "1", "a", "2", "xxx", "xxx"), "brad", "br1d"},
+
+		testCase{NewReplacer("a", "1", "aa", "2", "aaa", "3"), "aaaa", "1111"},
+
+		testCase{NewReplacer("aaa", "3", "aa", "2", "a", "1"), "aaaa", "31"},
+	)
+
+	// gen1 has multiple old strings of variable length. There is no
+	// overall non-empty common prefix, but some pairwise common prefixes.
+	gen1 := NewReplacer(
+		"aaa", "3[aaa]",
+		"aa", "2[aa]",
+		"a", "1[a]",
+		"i", "i",
+		"longerst", "most long",
+		"longer", "medium",
+		"long", "short",
+		"xx", "xx",
+		"x", "X",
+		"X", "Y",
+		"Y", "Z",
+	)
+	testCases = append(testCases,
+		testCase{gen1, "fooaaabar", "foo3[aaa]b1[a]r"},
+		testCase{gen1, "long, longerst, longer", "short, most long, medium"},
+		testCase{gen1, "xxxxx", "xxxxX"},
+		testCase{gen1, "XiX", "YiY"},
+		testCase{gen1, "", ""},
+	)
+
+	// gen2 has multiple old strings with no pairwise common prefix.
+	gen2 := NewReplacer(
+		"roses", "red",
+		"violets", "blue",
+		"sugar", "sweet",
+	)
+	testCases = append(testCases,
+		testCase{gen2, "roses are red, violets are blue...", "red are red, blue are blue..."},
+		testCase{gen2, "", ""},
+	)
+
+	// gen3 has multiple old strings with an overall common prefix.
+	gen3 := NewReplacer(
+		"abracadabra", "poof",
+		"abracadabrakazam", "splat",
+		"abraham", "lincoln",
+		"abrasion", "scrape",
+		"abraham", "isaac",
+	)
+	testCases = append(testCases,
+		testCase{gen3, "abracadabrakazam abraham", "poofkazam lincoln"},
+		testCase{gen3, "abrasion abracad", "scrape abracad"},
+		testCase{gen3, "abba abram abrasive", "abba abram abrasive"},
+		testCase{gen3, "", ""},
+	)
+
+	// foo{1,2,3,4} have multiple old strings with an overall common prefix
+	// and 1- or 2- byte extensions from the common prefix.
+	foo1 := NewReplacer(
+		"foo1", "A",
+		"foo2", "B",
+		"foo3", "C",
+	)
+	foo2 := NewReplacer(
+		"foo1", "A",
+		"foo2", "B",
+		"foo31", "C",
+		"foo32", "D",
+	)
+	foo3 := NewReplacer(
+		"foo11", "A",
+		"foo12", "B",
+		"foo31", "C",
+		"foo32", "D",
+	)
+	foo4 := NewReplacer(
+		"foo12", "B",
+		"foo32", "D",
+	)
+	testCases = append(testCases,
+		testCase{foo1, "fofoofoo12foo32oo", "fofooA2C2oo"},
+		testCase{foo1, "", ""},
+
+		testCase{foo2, "fofoofoo12foo32oo", "fofooA2Doo"},
+		testCase{foo2, "", ""},
+
+		testCase{foo3, "fofoofoo12foo32oo", "fofooBDoo"},
+		testCase{foo3, "", ""},
+
+		testCase{foo4, "fofoofoo12foo32oo", "fofooBDoo"},
+		testCase{foo4, "", ""},
+	)
+
+	// genAll maps "\x00\x01\x02...\xfe\xff" to "[all]", amongst other things.
+	allBytes := make([]byte, 256)
+	for i := range allBytes {
+		allBytes[i] = byte(i)
+	}
+	allString := string(allBytes)
+	genAll := NewReplacer(
+		allString, "[all]",
+		"\xff", "[ff]",
+		"\x00", "[00]",
+	)
+	testCases = append(testCases,
+		testCase{genAll, allString, "[all]"},
+		testCase{genAll, "a\xff" + allString + "\x00", "a[ff][all][00]"},
+		testCase{genAll, "", ""},
+	)
+
+	// Test cases with empty old strings.
+
+	blankToX1 := NewReplacer("", "X")
+	blankToX2 := NewReplacer("", "X", "", "")
+	blankHighPriority := NewReplacer("", "X", "o", "O")
+	blankLowPriority := NewReplacer("o", "O", "", "X")
+	blankNoOp1 := NewReplacer("", "")
+	blankNoOp2 := NewReplacer("", "", "", "A")
+	blankFoo := NewReplacer("", "X", "foobar", "R", "foobaz", "Z")
+	testCases = append(testCases,
+		testCase{blankToX1, "foo", "XfXoXoX"},
+		testCase{blankToX1, "", "X"},
+
+		testCase{blankToX2, "foo", "XfXoXoX"},
+		testCase{blankToX2, "", "X"},
+
+		testCase{blankHighPriority, "oo", "XOXOX"},
+		testCase{blankHighPriority, "ii", "XiXiX"},
+		testCase{blankHighPriority, "oiio", "XOXiXiXOX"},
+		testCase{blankHighPriority, "iooi", "XiXOXOXiX"},
+		testCase{blankHighPriority, "", "X"},
+
+		testCase{blankLowPriority, "oo", "OOX"},
+		testCase{blankLowPriority, "ii", "XiXiX"},
+		testCase{blankLowPriority, "oiio", "OXiXiOX"},
+		testCase{blankLowPriority, "iooi", "XiOOXiX"},
+		testCase{blankLowPriority, "", "X"},
+
+		testCase{blankNoOp1, "foo", "foo"},
+		testCase{blankNoOp1, "", ""},
+
+		testCase{blankNoOp2, "foo", "foo"},
+		testCase{blankNoOp2, "", ""},
+
+		testCase{blankFoo, "foobarfoobaz", "XRXZX"},
+		testCase{blankFoo, "foobar-foobaz", "XRX-XZX"},
+		testCase{blankFoo, "", "X"},
+	)
+
+	// single string replacer
+
+	abcMatcher := NewReplacer("abc", "[match]")
+
+	testCases = append(testCases,
+		testCase{abcMatcher, "", ""},
+		testCase{abcMatcher, "ab", "ab"},
+		testCase{abcMatcher, "abc", "[match]"},
+		testCase{abcMatcher, "abcd", "[match]d"},
+		testCase{abcMatcher, "cabcabcdabca", "c[match][match]d[match]a"},
+	)
+
+	// Issue 6659 cases (more single string replacer)
+
+	noHello := NewReplacer("Hello", "")
+	testCases = append(testCases,
+		testCase{noHello, "Hello", ""},
+		testCase{noHello, "Hellox", "x"},
+		testCase{noHello, "xHello", "x"},
+		testCase{noHello, "xHellox", "xx"},
+	)
+
+	// No-arg test cases.
+
+	nop := NewReplacer()
+	testCases = append(testCases,
+		testCase{nop, "abc", "abc"},
+		testCase{nop, "", ""},
+	)
+
+	// Run the test cases.
+
+	for i, tc := range testCases {
+		if s := tc.r.Replace(tc.in); s != tc.out {
+			t.Errorf("%d. Replace(%q) = %q, want %q", i, tc.in, s, tc.out)
+		}
+		var buf bytes.Buffer
+		n, err := tc.r.WriteString(&buf, tc.in)
+		if err != nil {
+			t.Errorf("%d. WriteString: %v", i, err)
+			continue
+		}
+		got := buf.String()
+		if got != tc.out {
+			t.Errorf("%d. WriteString(%q) wrote %q, want %q", i, tc.in, got, tc.out)
+			continue
+		}
+		if n != len(tc.out) {
+			t.Errorf("%d. WriteString(%q) wrote correct string but reported %d bytes; want %d (%q)",
+				i, tc.in, n, len(tc.out), tc.out)
+		}
+	}
+}
+
+var algorithmTestCases = []struct {
+	r    *Replacer
+	want string
+}{
+	{capitalLetters, "*strings.byteReplacer"},
+	{htmlEscaper, "*strings.byteStringReplacer"},
+	{NewReplacer("12", "123"), "*strings.singleStringReplacer"},
+	{NewReplacer("1", "12"), "*strings.byteStringReplacer"},
+	{NewReplacer("", "X"), "*strings.genericReplacer"},
+	{NewReplacer("a", "1", "b", "12", "cde", "123"), "*strings.genericReplacer"},
+}
+
+// TestPickAlgorithm tests that NewReplacer picks the correct algorithm.
+func TestPickAlgorithm(t *testing.T) {
+	for i, tc := range algorithmTestCases {
+		got := fmt.Sprintf("%T", tc.r.Replacer())
+		if got != tc.want {
+			t.Errorf("%d. algorithm = %s, want %s", i, got, tc.want)
+		}
+	}
+}
+
+type errWriter struct{}
+
+func (errWriter) Write(p []byte) (n int, err error) {
+	return 0, fmt.Errorf("unwritable")
+}
+
+// TestWriteStringError tests that WriteString returns an error
+// received from the underlying io.Writer.
+func TestWriteStringError(t *testing.T) {
+	for i, tc := range algorithmTestCases {
+		n, err := tc.r.WriteString(errWriter{}, "abc")
+		if n != 0 || err == nil || err.Error() != "unwritable" {
+			t.Errorf("%d. WriteStringError = %d, %v, want 0, unwritable", i, n, err)
+		}
+	}
+}
+
+// TestGenericTrieBuilding verifies the structure of the generated trie. There
+// is one node per line, and the key ending with the current line is in the
+// trie if it ends with a "+".
+func TestGenericTrieBuilding(t *testing.T) {
+	testCases := []struct{ in, out string }{
+		{"abc;abdef;abdefgh;xx;xy;z", `-
+			a-
+			.b-
+			..c+
+			..d-
+			...ef+
+			.....gh+
+			x-
+			.x+
+			.y+
+			z+
+			`},
+		{"abracadabra;abracadabrakazam;abraham;abrasion", `-
+			a-
+			.bra-
+			....c-
+			.....adabra+
+			...........kazam+
+			....h-
+			.....am+
+			....s-
+			.....ion+
+			`},
+		{"aaa;aa;a;i;longerst;longer;long;xx;x;X;Y", `-
+			X+
+			Y+
+			a+
+			.a+
+			..a+
+			i+
+			l-
+			.ong+
+			....er+
+			......st+
+			x+
+			.x+
+			`},
+		{"foo;;foo;foo1", `+
+			f-
+			.oo+
+			...1+
+			`},
+	}
+
+	for _, tc := range testCases {
+		keys := Split(tc.in, ";")
+		args := make([]string, len(keys)*2)
+		for i, key := range keys {
+			args[i*2] = key
+		}
+
+		got := NewReplacer(args...).PrintTrie()
+		// Remove tabs from tc.out
+		wantbuf := make([]byte, 0, len(tc.out))
+		for i := 0; i < len(tc.out); i++ {
+			if tc.out[i] != '\t' {
+				wantbuf = append(wantbuf, tc.out[i])
+			}
+		}
+		want := string(wantbuf)
+
+		if got != want {
+			t.Errorf("PrintTrie(%q)\ngot\n%swant\n%s", tc.in, got, want)
+		}
+	}
+}
+
+func BenchmarkGenericNoMatch(b *testing.B) {
+	str := Repeat("A", 100) + Repeat("B", 100)
+	generic := NewReplacer("a", "A", "b", "B", "12", "123") // varying lengths forces generic
+	for i := 0; i < b.N; i++ {
+		generic.Replace(str)
+	}
+}
+
+func BenchmarkGenericMatch1(b *testing.B) {
+	str := Repeat("a", 100) + Repeat("b", 100)
+	generic := NewReplacer("a", "A", "b", "B", "12", "123")
+	for i := 0; i < b.N; i++ {
+		generic.Replace(str)
+	}
+}
+
+func BenchmarkGenericMatch2(b *testing.B) {
+	str := Repeat("It&apos;s &lt;b&gt;HTML&lt;/b&gt;!", 100)
+	for i := 0; i < b.N; i++ {
+		htmlUnescaper.Replace(str)
+	}
+}
+
+func benchmarkSingleString(b *testing.B, pattern, text string) {
+	r := NewReplacer(pattern, "[match]")
+	b.SetBytes(int64(len(text)))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.Replace(text)
+	}
+}
+
+func BenchmarkSingleMaxSkipping(b *testing.B) {
+	benchmarkSingleString(b, Repeat("b", 25), Repeat("a", 10000))
+}
+
+func BenchmarkSingleLongSuffixFail(b *testing.B) {
+	benchmarkSingleString(b, "b"+Repeat("a", 500), Repeat("a", 1002))
+}
+
+func BenchmarkSingleMatch(b *testing.B) {
+	benchmarkSingleString(b, "abcdef", Repeat("abcdefghijklmno", 1000))
+}
+
+func BenchmarkByteByteNoMatch(b *testing.B) {
+	str := Repeat("A", 100) + Repeat("B", 100)
+	for i := 0; i < b.N; i++ {
+		capitalLetters.Replace(str)
+	}
+}
+
+func BenchmarkByteByteMatch(b *testing.B) {
+	str := Repeat("a", 100) + Repeat("b", 100)
+	for i := 0; i < b.N; i++ {
+		capitalLetters.Replace(str)
+	}
+}
+
+func BenchmarkByteStringMatch(b *testing.B) {
+	str := "<" + Repeat("a", 99) + Repeat("b", 99) + ">"
+	for i := 0; i < b.N; i++ {
+		htmlEscaper.Replace(str)
+	}
+}
+
+func BenchmarkHTMLEscapeNew(b *testing.B) {
+	str := "I <3 to escape HTML & other text too."
+	for i := 0; i < b.N; i++ {
+		htmlEscaper.Replace(str)
+	}
+}
+
+func BenchmarkHTMLEscapeOld(b *testing.B) {
+	str := "I <3 to escape HTML & other text too."
+	for i := 0; i < b.N; i++ {
+		oldHTMLEscape(str)
+	}
+}
+
+func BenchmarkByteStringReplacerWriteString(b *testing.B) {
+	str := Repeat("I <3 to escape HTML & other text too.", 100)
+	buf := new(bytes.Buffer)
+	for i := 0; i < b.N; i++ {
+		htmlEscaper.WriteString(buf, str)
+		buf.Reset()
+	}
+}
+
+func BenchmarkByteReplacerWriteString(b *testing.B) {
+	str := Repeat("abcdefghijklmnopqrstuvwxyz", 100)
+	buf := new(bytes.Buffer)
+	for i := 0; i < b.N; i++ {
+		capitalLetters.WriteString(buf, str)
+		buf.Reset()
+	}
+}
+
+// BenchmarkByteByteReplaces compares byteByteImpl against multiple Replaces.
+func BenchmarkByteByteReplaces(b *testing.B) {
+	str := Repeat("a", 100) + Repeat("b", 100)
+	for i := 0; i < b.N; i++ {
+		Replace(Replace(str, "a", "A", -1), "b", "B", -1)
+	}
+}
+
+// BenchmarkByteByteMap compares byteByteImpl against Map.
+func BenchmarkByteByteMap(b *testing.B) {
+	str := Repeat("a", 100) + Repeat("b", 100)
+	fn := func(r rune) rune {
+		switch r {
+		case 'a':
+			return 'A'
+		case 'b':
+			return 'B'
+		}
+		return r
+	}
+	for i := 0; i < b.N; i++ {
+		Map(fn, str)
+	}
+}
diff --git a/src/strings/search.go b/src/strings/search.go
new file mode 100644
index 000000000..f77c879c5
--- /dev/null
+++ b/src/strings/search.go
@@ -0,0 +1,124 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings
+
+// stringFinder efficiently finds strings in a source text. It's implemented
+// using the Boyer-Moore string search algorithm:
+// http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
+// http://www.cs.utexas.edu/~moore/publications/fstrpos.pdf (note: this aged
+// document uses 1-based indexing)
+type stringFinder struct {
+	// pattern is the string that we are searching for in the text.
+	pattern string
+
+	// badCharSkip[b] contains the distance between the last byte of pattern
+	// and the rightmost occurrence of b in pattern. If b is not in pattern,
+	// badCharSkip[b] is len(pattern).
+	//
+	// Whenever a mismatch is found with byte b in the text, we can safely
+	// shift the matching frame at least badCharSkip[b] until the next time
+	// the matching char could be in alignment.
+	badCharSkip [256]int
+
+	// goodSuffixSkip[i] defines how far we can shift the matching frame given
+	// that the suffix pattern[i+1:] matches, but the byte pattern[i] does
+	// not. There are two cases to consider:
+	//
+	// 1. The matched suffix occurs elsewhere in pattern (with a different
+	// byte preceding it that we might possibly match). In this case, we can
+	// shift the matching frame to align with the next suffix chunk. For
+	// example, the pattern "mississi" has the suffix "issi" next occurring
+	// (in right-to-left order) at index 1, so goodSuffixSkip[3] ==
+	// shift+len(suffix) == 3+4 == 7.
+	//
+	// 2. If the matched suffix does not occur elsewhere in pattern, then the
+	// matching frame may share part of its prefix with the end of the
+	// matching suffix. In this case, goodSuffixSkip[i] will contain how far
+	// to shift the frame to align this portion of the prefix to the
+	// suffix. For example, in the pattern "abcxxxabc", when the first
+	// mismatch from the back is found to be in position 3, the matching
+	// suffix "xxabc" is not found elsewhere in the pattern. However, its
+	// rightmost "abc" (at position 6) is a prefix of the whole pattern, so
+	// goodSuffixSkip[3] == shift+len(suffix) == 6+5 == 11.
+	goodSuffixSkip []int
+}
+
+func makeStringFinder(pattern string) *stringFinder {
+	f := &stringFinder{
+		pattern:        pattern,
+		goodSuffixSkip: make([]int, len(pattern)),
+	}
+	// last is the index of the last character in the pattern.
+	last := len(pattern) - 1
+
+	// Build bad character table.
+	// Bytes not in the pattern can skip one pattern's length.
+	for i := range f.badCharSkip {
+		f.badCharSkip[i] = len(pattern)
+	}
+	// The loop condition is < instead of <= so that the last byte does not
+	// have a zero distance to itself. Finding this byte out of place implies
+	// that it is not in the last position.
+	for i := 0; i < last; i++ {
+		f.badCharSkip[pattern[i]] = last - i
+	}
+
+	// Build good suffix table.
+	// First pass: set each value to the next index which starts a prefix of
+	// pattern.
+	lastPrefix := last
+	for i := last; i >= 0; i-- {
+		if HasPrefix(pattern, pattern[i+1:]) {
+			lastPrefix = i + 1
+		}
+		// lastPrefix is the shift, and (last-i) is len(suffix).
+		f.goodSuffixSkip[i] = lastPrefix + last - i
+	}
+	// Second pass: find repeats of pattern's suffix starting from the front.
+	for i := 0; i < last; i++ {
+		lenSuffix := longestCommonSuffix(pattern, pattern[1:i+1])
+		if pattern[i-lenSuffix] != pattern[last-lenSuffix] {
+			// (last-i) is the shift, and lenSuffix is len(suffix).
+			f.goodSuffixSkip[last-lenSuffix] = lenSuffix + last - i
+		}
+	}
+
+	return f
+}
+
+func longestCommonSuffix(a, b string) (i int) {
+	for ; i < len(a) && i < len(b); i++ {
+		if a[len(a)-1-i] != b[len(b)-1-i] {
+			break
+		}
+	}
+	return
+}
+
+// next returns the index in text of the first occurrence of the pattern. If
+// the pattern is not found, it returns -1.
+func (f *stringFinder) next(text string) int {
+	i := len(f.pattern) - 1
+	for i < len(text) {
+		// Compare backwards from the end until the first unmatching character.
+		j := len(f.pattern) - 1
+		for j >= 0 && text[i] == f.pattern[j] {
+			i--
+			j--
+		}
+		if j < 0 {
+			return i + 1 // match
+		}
+		i += max(f.badCharSkip[text[i]], f.goodSuffixSkip[j])
+	}
+	return -1
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
diff --git a/src/strings/search_test.go b/src/strings/search_test.go
new file mode 100644
index 000000000..966c05e65
--- /dev/null
+++ b/src/strings/search_test.go
@@ -0,0 +1,90 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings_test
+
+import (
+	"reflect"
+	. "strings"
+	"testing"
+)
+
+func TestFinderNext(t *testing.T) {
+	testCases := []struct {
+		pat, text string
+		index     int
+	}{
+		{"", "", 0},
+		{"", "abc", 0},
+		{"abc", "", -1},
+		{"abc", "abc", 0},
+		{"d", "abcdefg", 3},
+		{"nan", "banana", 2},
+		{"pan", "anpanman", 2},
+		{"nnaaman", "anpanmanam", -1},
+		{"abcd", "abc", -1},
+		{"abcd", "bcd", -1},
+		{"bcd", "abcd", 1},
+		{"abc", "acca", -1},
+		{"aa", "aaa", 0},
+		{"baa", "aaaaa", -1},
+		{"at that", "which finally halts.  at that point", 22},
+	}
+
+	for _, tc := range testCases {
+		got := StringFind(tc.pat, tc.text)
+		want := tc.index
+		if got != want {
+			t.Errorf("stringFind(%q, %q) got %d, want %d\n", tc.pat, tc.text, got, want)
+		}
+	}
+}
+
+func TestFinderCreation(t *testing.T) {
+	testCases := []struct {
+		pattern string
+		bad     [256]int
+		suf     []int
+	}{
+		{
+			"abc",
+			[256]int{'a': 2, 'b': 1, 'c': 3},
+			[]int{5, 4, 1},
+		},
+		{
+			"mississi",
+			[256]int{'i': 3, 'm': 7, 's': 1},
+			[]int{15, 14, 13, 7, 11, 10, 7, 1},
+		},
+		// From http://www.cs.utexas.edu/~moore/publications/fstrpos.pdf
+		{
+			"abcxxxabc",
+			[256]int{'a': 2, 'b': 1, 'c': 6, 'x': 3},
+			[]int{14, 13, 12, 11, 10, 9, 11, 10, 1},
+		},
+		{
+			"abyxcdeyx",
+			[256]int{'a': 8, 'b': 7, 'c': 4, 'd': 3, 'e': 2, 'y': 1, 'x': 5},
+			[]int{17, 16, 15, 14, 13, 12, 7, 10, 1},
+		},
+	}
+
+	for _, tc := range testCases {
+		bad, good := DumpTables(tc.pattern)
+
+		for i, got := range bad {
+			want := tc.bad[i]
+			if want == 0 {
+				want = len(tc.pattern)
+			}
+			if got != want {
+				t.Errorf("boyerMoore(%q) bad['%c']: got %d want %d", tc.pattern, i, got, want)
+			}
+		}
+
+		if !reflect.DeepEqual(good, tc.suf) {
+			t.Errorf("boyerMoore(%q) got %v want %v", tc.pattern, good, tc.suf)
+		}
+	}
+}
diff --git a/src/strings/strings.go b/src/strings/strings.go
new file mode 100644
index 000000000..761f32a06
--- /dev/null
+++ b/src/strings/strings.go
@@ -0,0 +1,765 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package strings implements simple functions to manipulate strings.
+package strings
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// explode splits s into an array of UTF-8 sequences, one per Unicode character (still strings) up to a maximum of n (n < 0 means no limit).
+// Invalid UTF-8 sequences become correct encodings of U+FFF8.
+func explode(s string, n int) []string {
+	if n == 0 {
+		return nil
+	}
+	l := utf8.RuneCountInString(s)
+	if n <= 0 || n > l {
+		n = l
+	}
+	a := make([]string, n)
+	var size int
+	var ch rune
+	i, cur := 0, 0
+	for ; i+1 < n; i++ {
+		ch, size = utf8.DecodeRuneInString(s[cur:])
+		if ch == utf8.RuneError {
+			a[i] = string(utf8.RuneError)
+		} else {
+			a[i] = s[cur : cur+size]
+		}
+		cur += size
+	}
+	// add the rest, if there is any
+	if cur < len(s) {
+		a[i] = s[cur:]
+	}
+	return a
+}
+
+// primeRK is the prime base used in Rabin-Karp algorithm.
+const primeRK = 16777619
+
+// hashStr returns the hash and the appropriate multiplicative
+// factor for use in Rabin-Karp algorithm.
+func hashStr(sep string) (uint32, uint32) {
+	hash := uint32(0)
+	for i := 0; i < len(sep); i++ {
+		hash = hash*primeRK + uint32(sep[i])
+	}
+	var pow, sq uint32 = 1, primeRK
+	for i := len(sep); i > 0; i >>= 1 {
+		if i&1 != 0 {
+			pow *= sq
+		}
+		sq *= sq
+	}
+	return hash, pow
+}
+
+// hashStrRev returns the hash of the reverse of sep and the
+// appropriate multiplicative factor for use in Rabin-Karp algorithm.
+func hashStrRev(sep string) (uint32, uint32) {
+	hash := uint32(0)
+	for i := len(sep) - 1; i >= 0; i-- {
+		hash = hash*primeRK + uint32(sep[i])
+	}
+	var pow, sq uint32 = 1, primeRK
+	for i := len(sep); i > 0; i >>= 1 {
+		if i&1 != 0 {
+			pow *= sq
+		}
+		sq *= sq
+	}
+	return hash, pow
+}
+
+// Count counts the number of non-overlapping instances of sep in s.
+func Count(s, sep string) int {
+	n := 0
+	// special cases
+	switch {
+	case len(sep) == 0:
+		return utf8.RuneCountInString(s) + 1
+	case len(sep) == 1:
+		// special case worth making fast
+		c := sep[0]
+		for i := 0; i < len(s); i++ {
+			if s[i] == c {
+				n++
+			}
+		}
+		return n
+	case len(sep) > len(s):
+		return 0
+	case len(sep) == len(s):
+		if sep == s {
+			return 1
+		}
+		return 0
+	}
+	// Rabin-Karp search
+	hashsep, pow := hashStr(sep)
+	h := uint32(0)
+	for i := 0; i < len(sep); i++ {
+		h = h*primeRK + uint32(s[i])
+	}
+	lastmatch := 0
+	if h == hashsep && s[:len(sep)] == sep {
+		n++
+		lastmatch = len(sep)
+	}
+	for i := len(sep); i < len(s); {
+		h *= primeRK
+		h += uint32(s[i])
+		h -= pow * uint32(s[i-len(sep)])
+		i++
+		if h == hashsep && lastmatch <= i-len(sep) && s[i-len(sep):i] == sep {
+			n++
+			lastmatch = i
+		}
+	}
+	return n
+}
+
+// Contains returns true if substr is within s.
+func Contains(s, substr string) bool {
+	return Index(s, substr) >= 0
+}
+
+// ContainsAny returns true if any Unicode code points in chars are within s.
+func ContainsAny(s, chars string) bool {
+	return IndexAny(s, chars) >= 0
+}
+
+// ContainsRune returns true if the Unicode code point r is within s.
+func ContainsRune(s string, r rune) bool {
+	return IndexRune(s, r) >= 0
+}
+
+// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
+func Index(s, sep string) int {
+	n := len(sep)
+	switch {
+	case n == 0:
+		return 0
+	case n == 1:
+		return IndexByte(s, sep[0])
+	case n == len(s):
+		if sep == s {
+			return 0
+		}
+		return -1
+	case n > len(s):
+		return -1
+	}
+	// Rabin-Karp search
+	hashsep, pow := hashStr(sep)
+	var h uint32
+	for i := 0; i < n; i++ {
+		h = h*primeRK + uint32(s[i])
+	}
+	if h == hashsep && s[:n] == sep {
+		return 0
+	}
+	for i := n; i < len(s); {
+		h *= primeRK
+		h += uint32(s[i])
+		h -= pow * uint32(s[i-n])
+		i++
+		if h == hashsep && s[i-n:i] == sep {
+			return i - n
+		}
+	}
+	return -1
+}
+
+// LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
+func LastIndex(s, sep string) int {
+	n := len(sep)
+	switch {
+	case n == 0:
+		return len(s)
+	case n == 1:
+		// special case worth making fast
+		c := sep[0]
+		for i := len(s) - 1; i >= 0; i-- {
+			if s[i] == c {
+				return i
+			}
+		}
+		return -1
+	case n == len(s):
+		if sep == s {
+			return 0
+		}
+		return -1
+	case n > len(s):
+		return -1
+	}
+	// Rabin-Karp search from the end of the string
+	hashsep, pow := hashStrRev(sep)
+	last := len(s) - n
+	var h uint32
+	for i := len(s) - 1; i >= last; i-- {
+		h = h*primeRK + uint32(s[i])
+	}
+	if h == hashsep && s[last:] == sep {
+		return last
+	}
+	for i := last - 1; i >= 0; i-- {
+		h *= primeRK
+		h += uint32(s[i])
+		h -= pow * uint32(s[i+n])
+		if h == hashsep && s[i:i+n] == sep {
+			return i
+		}
+	}
+	return -1
+}
+
+// IndexRune returns the index of the first instance of the Unicode code point
+// r, or -1 if rune is not present in s.
+func IndexRune(s string, r rune) int {
+	switch {
+	case r < 0x80:
+		b := byte(r)
+		for i := 0; i < len(s); i++ {
+			if s[i] == b {
+				return i
+			}
+		}
+	default:
+		for i, c := range s {
+			if c == r {
+				return i
+			}
+		}
+	}
+	return -1
+}
+
+// IndexAny returns the index of the first instance of any Unicode code point
+// from chars in s, or -1 if no Unicode code point from chars is present in s.
+func IndexAny(s, chars string) int {
+	if len(chars) > 0 {
+		for i, c := range s {
+			for _, m := range chars {
+				if c == m {
+					return i
+				}
+			}
+		}
+	}
+	return -1
+}
+
+// LastIndexAny returns the index of the last instance of any Unicode code
+// point from chars in s, or -1 if no Unicode code point from chars is
+// present in s.
+func LastIndexAny(s, chars string) int {
+	if len(chars) > 0 {
+		for i := len(s); i > 0; {
+			rune, size := utf8.DecodeLastRuneInString(s[0:i])
+			i -= size
+			for _, m := range chars {
+				if rune == m {
+					return i
+				}
+			}
+		}
+	}
+	return -1
+}
+
+// Generic split: splits after each instance of sep,
+// including sepSave bytes of sep in the subarrays.
+func genSplit(s, sep string, sepSave, n int) []string {
+	if n == 0 {
+		return nil
+	}
+	if sep == "" {
+		return explode(s, n)
+	}
+	if n < 0 {
+		n = Count(s, sep) + 1
+	}
+	c := sep[0]
+	start := 0
+	a := make([]string, n)
+	na := 0
+	for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
+		if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
+			a[na] = s[start : i+sepSave]
+			na++
+			start = i + len(sep)
+			i += len(sep) - 1
+		}
+	}
+	a[na] = s[start:]
+	return a[0 : na+1]
+}
+
+// SplitN slices s into substrings separated by sep and returns a slice of
+// the substrings between those separators.
+// If sep is empty, SplitN splits after each UTF-8 sequence.
+// The count determines the number of substrings to return:
+//   n > 0: at most n substrings; the last substring will be the unsplit remainder.
+//   n == 0: the result is nil (zero substrings)
+//   n < 0: all substrings
+func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
+
+// SplitAfterN slices s into substrings after each instance of sep and
+// returns a slice of those substrings.
+// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
+// The count determines the number of substrings to return:
+//   n > 0: at most n substrings; the last substring will be the unsplit remainder.
+//   n == 0: the result is nil (zero substrings)
+//   n < 0: all substrings
+func SplitAfterN(s, sep string, n int) []string {
+	return genSplit(s, sep, len(sep), n)
+}
+
+// Split slices s into all substrings separated by sep and returns a slice of
+// the substrings between those separators.
+// If sep is empty, Split splits after each UTF-8 sequence.
+// It is equivalent to SplitN with a count of -1.
+func Split(s, sep string) []string { return genSplit(s, sep, 0, -1) }
+
+// SplitAfter slices s into all substrings after each instance of sep and
+// returns a slice of those substrings.
+// If sep is empty, SplitAfter splits after each UTF-8 sequence.
+// It is equivalent to SplitAfterN with a count of -1.
+func SplitAfter(s, sep string) []string {
+	return genSplit(s, sep, len(sep), -1)
+}
+
+// Fields splits the string s around each instance of one or more consecutive white space
+// characters, as defined by unicode.IsSpace, returning an array of substrings of s or an
+// empty list if s contains only white space.
+func Fields(s string) []string {
+	return FieldsFunc(s, unicode.IsSpace)
+}
+
+// FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
+// and returns an array of slices of s. If all code points in s satisfy f(c) or the
+// string is empty, an empty slice is returned.
+func FieldsFunc(s string, f func(rune) bool) []string {
+	// First count the fields.
+	n := 0
+	inField := false
+	for _, rune := range s {
+		wasInField := inField
+		inField = !f(rune)
+		if inField && !wasInField {
+			n++
+		}
+	}
+
+	// Now create them.
+	a := make([]string, n)
+	na := 0
+	fieldStart := -1 // Set to -1 when looking for start of field.
+	for i, rune := range s {
+		if f(rune) {
+			if fieldStart >= 0 {
+				a[na] = s[fieldStart:i]
+				na++
+				fieldStart = -1
+			}
+		} else if fieldStart == -1 {
+			fieldStart = i
+		}
+	}
+	if fieldStart >= 0 { // Last field might end at EOF.
+		a[na] = s[fieldStart:]
+	}
+	return a
+}
+
+// Join concatenates the elements of a to create a single string.   The separator string
+// sep is placed between elements in the resulting string.
+func Join(a []string, sep string) string {
+	if len(a) == 0 {
+		return ""
+	}
+	if len(a) == 1 {
+		return a[0]
+	}
+	n := len(sep) * (len(a) - 1)
+	for i := 0; i < len(a); i++ {
+		n += len(a[i])
+	}
+
+	b := make([]byte, n)
+	bp := copy(b, a[0])
+	for _, s := range a[1:] {
+		bp += copy(b[bp:], sep)
+		bp += copy(b[bp:], s)
+	}
+	return string(b)
+}
+
+// HasPrefix tests whether the string s begins with prefix.
+func HasPrefix(s, prefix string) bool {
+	return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
+}
+
+// HasSuffix tests whether the string s ends with suffix.
+func HasSuffix(s, suffix string) bool {
+	return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
+}
+
+// Map returns a copy of the string s with all its characters modified
+// according to the mapping function. If mapping returns a negative value, the character is
+// dropped from the string with no replacement.
+func Map(mapping func(rune) rune, s string) string {
+	// In the worst case, the string can grow when mapped, making
+	// things unpleasant.  But it's so rare we barge in assuming it's
+	// fine.  It could also shrink but that falls out naturally.
+	maxbytes := len(s) // length of b
+	nbytes := 0        // number of bytes encoded in b
+	// The output buffer b is initialized on demand, the first
+	// time a character differs.
+	var b []byte
+
+	for i, c := range s {
+		r := mapping(c)
+		if b == nil {
+			if r == c {
+				continue
+			}
+			b = make([]byte, maxbytes)
+			nbytes = copy(b, s[:i])
+		}
+		if r >= 0 {
+			wid := 1
+			if r >= utf8.RuneSelf {
+				wid = utf8.RuneLen(r)
+			}
+			if nbytes+wid > maxbytes {
+				// Grow the buffer.
+				maxbytes = maxbytes*2 + utf8.UTFMax
+				nb := make([]byte, maxbytes)
+				copy(nb, b[0:nbytes])
+				b = nb
+			}
+			nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
+		}
+	}
+	if b == nil {
+		return s
+	}
+	return string(b[0:nbytes])
+}
+
+// Repeat returns a new string consisting of count copies of the string s.
+func Repeat(s string, count int) string {
+	b := make([]byte, len(s)*count)
+	bp := copy(b, s)
+	for bp < len(b) {
+		copy(b[bp:], b[:bp])
+		bp *= 2
+	}
+	return string(b)
+}
+
+// ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
+func ToUpper(s string) string { return Map(unicode.ToUpper, s) }
+
+// ToLower returns a copy of the string s with all Unicode letters mapped to their lower case.
+func ToLower(s string) string { return Map(unicode.ToLower, s) }
+
+// ToTitle returns a copy of the string s with all Unicode letters mapped to their title case.
+func ToTitle(s string) string { return Map(unicode.ToTitle, s) }
+
+// ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
+// upper case, giving priority to the special casing rules.
+func ToUpperSpecial(_case unicode.SpecialCase, s string) string {
+	return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
+}
+
+// ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
+// lower case, giving priority to the special casing rules.
+func ToLowerSpecial(_case unicode.SpecialCase, s string) string {
+	return Map(func(r rune) rune { return _case.ToLower(r) }, s)
+}
+
+// ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
+// title case, giving priority to the special casing rules.
+func ToTitleSpecial(_case unicode.SpecialCase, s string) string {
+	return Map(func(r rune) rune { return _case.ToTitle(r) }, s)
+}
+
+// isSeparator reports whether the rune could mark a word boundary.
+// TODO: update when package unicode captures more of the properties.
+func isSeparator(r rune) bool {
+	// ASCII alphanumerics and underscore are not separators
+	if r <= 0x7F {
+		switch {
+		case '0' <= r && r <= '9':
+			return false
+		case 'a' <= r && r <= 'z':
+			return false
+		case 'A' <= r && r <= 'Z':
+			return false
+		case r == '_':
+			return false
+		}
+		return true
+	}
+	// Letters and digits are not separators
+	if unicode.IsLetter(r) || unicode.IsDigit(r) {
+		return false
+	}
+	// Otherwise, all we can do for now is treat spaces as separators.
+	return unicode.IsSpace(r)
+}
+
+// Title returns a copy of the string s with all Unicode letters that begin words
+// mapped to their title case.
+//
+// BUG: The rule Title uses for word boundaries does not handle Unicode punctuation properly.
+func Title(s string) string {
+	// Use a closure here to remember state.
+	// Hackish but effective. Depends on Map scanning in order and calling
+	// the closure once per rune.
+	prev := ' '
+	return Map(
+		func(r rune) rune {
+			if isSeparator(prev) {
+				prev = r
+				return unicode.ToTitle(r)
+			}
+			prev = r
+			return r
+		},
+		s)
+}
+
+// TrimLeftFunc returns a slice of the string s with all leading
+// Unicode code points c satisfying f(c) removed.
+func TrimLeftFunc(s string, f func(rune) bool) string {
+	i := indexFunc(s, f, false)
+	if i == -1 {
+		return ""
+	}
+	return s[i:]
+}
+
+// TrimRightFunc returns a slice of the string s with all trailing
+// Unicode code points c satisfying f(c) removed.
+func TrimRightFunc(s string, f func(rune) bool) string {
+	i := lastIndexFunc(s, f, false)
+	if i >= 0 && s[i] >= utf8.RuneSelf {
+		_, wid := utf8.DecodeRuneInString(s[i:])
+		i += wid
+	} else {
+		i++
+	}
+	return s[0:i]
+}
+
+// TrimFunc returns a slice of the string s with all leading
+// and trailing Unicode code points c satisfying f(c) removed.
+func TrimFunc(s string, f func(rune) bool) string {
+	return TrimRightFunc(TrimLeftFunc(s, f), f)
+}
+
+// IndexFunc returns the index into s of the first Unicode
+// code point satisfying f(c), or -1 if none do.
+func IndexFunc(s string, f func(rune) bool) int {
+	return indexFunc(s, f, true)
+}
+
+// LastIndexFunc returns the index into s of the last
+// Unicode code point satisfying f(c), or -1 if none do.
+func LastIndexFunc(s string, f func(rune) bool) int {
+	return lastIndexFunc(s, f, true)
+}
+
+// indexFunc is the same as IndexFunc except that if
+// truth==false, the sense of the predicate function is
+// inverted.
+func indexFunc(s string, f func(rune) bool, truth bool) int {
+	start := 0
+	for start < len(s) {
+		wid := 1
+		r := rune(s[start])
+		if r >= utf8.RuneSelf {
+			r, wid = utf8.DecodeRuneInString(s[start:])
+		}
+		if f(r) == truth {
+			return start
+		}
+		start += wid
+	}
+	return -1
+}
+
+// lastIndexFunc is the same as LastIndexFunc except that if
+// truth==false, the sense of the predicate function is
+// inverted.
+func lastIndexFunc(s string, f func(rune) bool, truth bool) int {
+	for i := len(s); i > 0; {
+		r, size := utf8.DecodeLastRuneInString(s[0:i])
+		i -= size
+		if f(r) == truth {
+			return i
+		}
+	}
+	return -1
+}
+
+func makeCutsetFunc(cutset string) func(rune) bool {
+	return func(r rune) bool { return IndexRune(cutset, r) >= 0 }
+}
+
+// Trim returns a slice of the string s with all leading and
+// trailing Unicode code points contained in cutset removed.
+func Trim(s string, cutset string) string {
+	if s == "" || cutset == "" {
+		return s
+	}
+	return TrimFunc(s, makeCutsetFunc(cutset))
+}
+
+// TrimLeft returns a slice of the string s with all leading
+// Unicode code points contained in cutset removed.
+func TrimLeft(s string, cutset string) string {
+	if s == "" || cutset == "" {
+		return s
+	}
+	return TrimLeftFunc(s, makeCutsetFunc(cutset))
+}
+
+// TrimRight returns a slice of the string s, with all trailing
+// Unicode code points contained in cutset removed.
+func TrimRight(s string, cutset string) string {
+	if s == "" || cutset == "" {
+		return s
+	}
+	return TrimRightFunc(s, makeCutsetFunc(cutset))
+}
+
+// TrimSpace returns a slice of the string s, with all leading
+// and trailing white space removed, as defined by Unicode.
+func TrimSpace(s string) string {
+	return TrimFunc(s, unicode.IsSpace)
+}
+
+// TrimPrefix returns s without the provided leading prefix string.
+// If s doesn't start with prefix, s is returned unchanged.
+func TrimPrefix(s, prefix string) string {
+	if HasPrefix(s, prefix) {
+		return s[len(prefix):]
+	}
+	return s
+}
+
+// TrimSuffix returns s without the provided trailing suffix string.
+// If s doesn't end with suffix, s is returned unchanged.
+func TrimSuffix(s, suffix string) string {
+	if HasSuffix(s, suffix) {
+		return s[:len(s)-len(suffix)]
+	}
+	return s
+}
+
+// Replace returns a copy of the string s with the first n
+// non-overlapping instances of old replaced by new.
+// If old is empty, it matches at the beginning of the string
+// and after each UTF-8 sequence, yielding up to k+1 replacements
+// for a k-rune string.
+// If n < 0, there is no limit on the number of replacements.
+func Replace(s, old, new string, n int) string {
+	if old == new || n == 0 {
+		return s // avoid allocation
+	}
+
+	// Compute number of replacements.
+	if m := Count(s, old); m == 0 {
+		return s // avoid allocation
+	} else if n < 0 || m < n {
+		n = m
+	}
+
+	// Apply replacements to buffer.
+	t := make([]byte, len(s)+n*(len(new)-len(old)))
+	w := 0
+	start := 0
+	for i := 0; i < n; i++ {
+		j := start
+		if len(old) == 0 {
+			if i > 0 {
+				_, wid := utf8.DecodeRuneInString(s[start:])
+				j += wid
+			}
+		} else {
+			j += Index(s[start:], old)
+		}
+		w += copy(t[w:], s[start:j])
+		w += copy(t[w:], new)
+		start = j + len(old)
+	}
+	w += copy(t[w:], s[start:])
+	return string(t[0:w])
+}
+
+// EqualFold reports whether s and t, interpreted as UTF-8 strings,
+// are equal under Unicode case-folding.
+func EqualFold(s, t string) bool {
+	for s != "" && t != "" {
+		// Extract first rune from each string.
+		var sr, tr rune
+		if s[0] < utf8.RuneSelf {
+			sr, s = rune(s[0]), s[1:]
+		} else {
+			r, size := utf8.DecodeRuneInString(s)
+			sr, s = r, s[size:]
+		}
+		if t[0] < utf8.RuneSelf {
+			tr, t = rune(t[0]), t[1:]
+		} else {
+			r, size := utf8.DecodeRuneInString(t)
+			tr, t = r, t[size:]
+		}
+
+		// If they match, keep going; if not, return false.
+
+		// Easy case.
+		if tr == sr {
+			continue
+		}
+
+		// Make sr < tr to simplify what follows.
+		if tr < sr {
+			tr, sr = sr, tr
+		}
+		// Fast check for ASCII.
+		if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' {
+			// ASCII, and sr is upper case.  tr must be lower case.
+			if tr == sr+'a'-'A' {
+				continue
+			}
+			return false
+		}
+
+		// General case.  SimpleFold(x) returns the next equivalent rune > x
+		// or wraps around to smaller values.
+		r := unicode.SimpleFold(sr)
+		for r != sr && r < tr {
+			r = unicode.SimpleFold(r)
+		}
+		if r == tr {
+			continue
+		}
+		return false
+	}
+
+	// One string is empty.  Are both?
+	return s == t
+}
diff --git a/src/strings/strings.s b/src/strings/strings.s
new file mode 100644
index 000000000..55103bae0
--- /dev/null
+++ b/src/strings/strings.s
@@ -0,0 +1,5 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is here just to make the go tool happy.
diff --git a/src/strings/strings_decl.go b/src/strings/strings_decl.go
new file mode 100644
index 000000000..810a696af
--- /dev/null
+++ b/src/strings/strings_decl.go
@@ -0,0 +1,8 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings
+
+// IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.
+func IndexByte(s string, c byte) int // ../runtime/asm_$GOARCH.s
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
new file mode 100644
index 000000000..7bb81ef3c
--- /dev/null
+++ b/src/strings/strings_test.go
@@ -0,0 +1,1204 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strings_test
+
+import (
+	"bytes"
+	"io"
+	"math/rand"
+	"reflect"
+	. "strings"
+	"testing"
+	"unicode"
+	"unicode/utf8"
+	"unsafe"
+)
+
+func eq(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := 0; i < len(a); i++ {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+var abcd = "abcd"
+var faces = "☺☻☹"
+var commas = "1,2,3,4"
+var dots = "1....2....3....4"
+
+type IndexTest struct {
+	s   string
+	sep string
+	out int
+}
+
+var indexTests = []IndexTest{
+	{"", "", 0},
+	{"", "a", -1},
+	{"", "foo", -1},
+	{"fo", "foo", -1},
+	{"foo", "foo", 0},
+	{"oofofoofooo", "f", 2},
+	{"oofofoofooo", "foo", 4},
+	{"barfoobarfoo", "foo", 3},
+	{"foo", "", 0},
+	{"foo", "o", 1},
+	{"abcABCabc", "A", 3},
+	// cases with one byte strings - test special case in Index()
+	{"", "a", -1},
+	{"x", "a", -1},
+	{"x", "x", 0},
+	{"abc", "a", 0},
+	{"abc", "b", 1},
+	{"abc", "c", 2},
+	{"abc", "x", -1},
+}
+
+var lastIndexTests = []IndexTest{
+	{"", "", 0},
+	{"", "a", -1},
+	{"", "foo", -1},
+	{"fo", "foo", -1},
+	{"foo", "foo", 0},
+	{"foo", "f", 0},
+	{"oofofoofooo", "f", 7},
+	{"oofofoofooo", "foo", 7},
+	{"barfoobarfoo", "foo", 9},
+	{"foo", "", 3},
+	{"foo", "o", 2},
+	{"abcABCabc", "A", 3},
+	{"abcABCabc", "a", 6},
+}
+
+var indexAnyTests = []IndexTest{
+	{"", "", -1},
+	{"", "a", -1},
+	{"", "abc", -1},
+	{"a", "", -1},
+	{"a", "a", 0},
+	{"aaa", "a", 0},
+	{"abc", "xyz", -1},
+	{"abc", "xcz", 2},
+	{"a☺b☻c☹d", "uvw☻xyz", 2 + len("☺")},
+	{"aRegExp*", ".(|)*+?^$[]", 7},
+	{dots + dots + dots, " ", -1},
+}
+var lastIndexAnyTests = []IndexTest{
+	{"", "", -1},
+	{"", "a", -1},
+	{"", "abc", -1},
+	{"a", "", -1},
+	{"a", "a", 0},
+	{"aaa", "a", 2},
+	{"abc", "xyz", -1},
+	{"abc", "ab", 1},
+	{"a☺b☻c☹d", "uvw☻xyz", 2 + len("☺")},
+	{"a.RegExp*", ".(|)*+?^$[]", 8},
+	{dots + dots + dots, " ", -1},
+}
+
+// Execute f on each test case.  funcName should be the name of f; it's used
+// in failure reports.
+func runIndexTests(t *testing.T, f func(s, sep string) int, funcName string, testCases []IndexTest) {
+	for _, test := range testCases {
+		actual := f(test.s, test.sep)
+		if actual != test.out {
+			t.Errorf("%s(%q,%q) = %v; want %v", funcName, test.s, test.sep, actual, test.out)
+		}
+	}
+}
+
+func TestIndex(t *testing.T)        { runIndexTests(t, Index, "Index", indexTests) }
+func TestLastIndex(t *testing.T)    { runIndexTests(t, LastIndex, "LastIndex", lastIndexTests) }
+func TestIndexAny(t *testing.T)     { runIndexTests(t, IndexAny, "IndexAny", indexAnyTests) }
+func TestLastIndexAny(t *testing.T) { runIndexTests(t, LastIndexAny, "LastIndexAny", lastIndexAnyTests) }
+
+var indexRuneTests = []struct {
+	s    string
+	rune rune
+	out  int
+}{
+	{"a A x", 'A', 2},
+	{"some_text=some_value", '=', 9},
+	{"☺a", 'a', 3},
+	{"a☻☺b", '☺', 4},
+}
+
+func TestIndexRune(t *testing.T) {
+	for _, test := range indexRuneTests {
+		if actual := IndexRune(test.s, test.rune); actual != test.out {
+			t.Errorf("IndexRune(%q,%d)= %v; want %v", test.s, test.rune, actual, test.out)
+		}
+	}
+}
+
+const benchmarkString = "some_text=some☺value"
+
+func BenchmarkIndexRune(b *testing.B) {
+	if got := IndexRune(benchmarkString, '☺'); got != 14 {
+		b.Fatalf("wrong index: expected 14, got=%d", got)
+	}
+	for i := 0; i < b.N; i++ {
+		IndexRune(benchmarkString, '☺')
+	}
+}
+
+func BenchmarkIndexRuneFastPath(b *testing.B) {
+	if got := IndexRune(benchmarkString, 'v'); got != 17 {
+		b.Fatalf("wrong index: expected 17, got=%d", got)
+	}
+	for i := 0; i < b.N; i++ {
+		IndexRune(benchmarkString, 'v')
+	}
+}
+
+func BenchmarkIndex(b *testing.B) {
+	if got := Index(benchmarkString, "v"); got != 17 {
+		b.Fatalf("wrong index: expected 17, got=%d", got)
+	}
+	for i := 0; i < b.N; i++ {
+		Index(benchmarkString, "v")
+	}
+}
+
+func BenchmarkLastIndex(b *testing.B) {
+	if got := Index(benchmarkString, "v"); got != 17 {
+		b.Fatalf("wrong index: expected 17, got=%d", got)
+	}
+	for i := 0; i < b.N; i++ {
+		LastIndex(benchmarkString, "v")
+	}
+}
+
+func BenchmarkIndexByte(b *testing.B) {
+	if got := IndexByte(benchmarkString, 'v'); got != 17 {
+		b.Fatalf("wrong index: expected 17, got=%d", got)
+	}
+	for i := 0; i < b.N; i++ {
+		IndexByte(benchmarkString, 'v')
+	}
+}
+
+var explodetests = []struct {
+	s string
+	n int
+	a []string
+}{
+	{"", -1, []string{}},
+	{abcd, 4, []string{"a", "b", "c", "d"}},
+	{faces, 3, []string{"☺", "☻", "☹"}},
+	{abcd, 2, []string{"a", "bcd"}},
+}
+
+func TestExplode(t *testing.T) {
+	for _, tt := range explodetests {
+		a := SplitN(tt.s, "", tt.n)
+		if !eq(a, tt.a) {
+			t.Errorf("explode(%q, %d) = %v; want %v", tt.s, tt.n, a, tt.a)
+			continue
+		}
+		s := Join(a, "")
+		if s != tt.s {
+			t.Errorf(`Join(explode(%q, %d), "") = %q`, tt.s, tt.n, s)
+		}
+	}
+}
+
+type SplitTest struct {
+	s   string
+	sep string
+	n   int
+	a   []string
+}
+
+var splittests = []SplitTest{
+	{abcd, "a", 0, nil},
+	{abcd, "a", -1, []string{"", "bcd"}},
+	{abcd, "z", -1, []string{"abcd"}},
+	{abcd, "", -1, []string{"a", "b", "c", "d"}},
+	{commas, ",", -1, []string{"1", "2", "3", "4"}},
+	{dots, "...", -1, []string{"1", ".2", ".3", ".4"}},
+	{faces, "☹", -1, []string{"☺☻", ""}},
+	{faces, "~", -1, []string{faces}},
+	{faces, "", -1, []string{"☺", "☻", "☹"}},
+	{"1 2 3 4", " ", 3, []string{"1", "2", "3 4"}},
+	{"1 2", " ", 3, []string{"1", "2"}},
+	{"123", "", 2, []string{"1", "23"}},
+	{"123", "", 17, []string{"1", "2", "3"}},
+}
+
+func TestSplit(t *testing.T) {
+	for _, tt := range splittests {
+		a := SplitN(tt.s, tt.sep, tt.n)
+		if !eq(a, tt.a) {
+			t.Errorf("Split(%q, %q, %d) = %v; want %v", tt.s, tt.sep, tt.n, a, tt.a)
+			continue
+		}
+		if tt.n == 0 {
+			continue
+		}
+		s := Join(a, tt.sep)
+		if s != tt.s {
+			t.Errorf("Join(Split(%q, %q, %d), %q) = %q", tt.s, tt.sep, tt.n, tt.sep, s)
+		}
+		if tt.n < 0 {
+			b := Split(tt.s, tt.sep)
+			if !reflect.DeepEqual(a, b) {
+				t.Errorf("Split disagrees with SplitN(%q, %q, %d) = %v; want %v", tt.s, tt.sep, tt.n, b, a)
+			}
+		}
+	}
+}
+
+var splitaftertests = []SplitTest{
+	{abcd, "a", -1, []string{"a", "bcd"}},
+	{abcd, "z", -1, []string{"abcd"}},
+	{abcd, "", -1, []string{"a", "b", "c", "d"}},
+	{commas, ",", -1, []string{"1,", "2,", "3,", "4"}},
+	{dots, "...", -1, []string{"1...", ".2...", ".3...", ".4"}},
+	{faces, "☹", -1, []string{"☺☻☹", ""}},
+	{faces, "~", -1, []string{faces}},
+	{faces, "", -1, []string{"☺", "☻", "☹"}},
+	{"1 2 3 4", " ", 3, []string{"1 ", "2 ", "3 4"}},
+	{"1 2 3", " ", 3, []string{"1 ", "2 ", "3"}},
+	{"1 2", " ", 3, []string{"1 ", "2"}},
+	{"123", "", 2, []string{"1", "23"}},
+	{"123", "", 17, []string{"1", "2", "3"}},
+}
+
+func TestSplitAfter(t *testing.T) {
+	for _, tt := range splitaftertests {
+		a := SplitAfterN(tt.s, tt.sep, tt.n)
+		if !eq(a, tt.a) {
+			t.Errorf(`Split(%q, %q, %d) = %v; want %v`, tt.s, tt.sep, tt.n, a, tt.a)
+			continue
+		}
+		s := Join(a, "")
+		if s != tt.s {
+			t.Errorf(`Join(Split(%q, %q, %d), %q) = %q`, tt.s, tt.sep, tt.n, tt.sep, s)
+		}
+		if tt.n < 0 {
+			b := SplitAfter(tt.s, tt.sep)
+			if !reflect.DeepEqual(a, b) {
+				t.Errorf("SplitAfter disagrees with SplitAfterN(%q, %q, %d) = %v; want %v", tt.s, tt.sep, tt.n, b, a)
+			}
+		}
+	}
+}
+
+type FieldsTest struct {
+	s string
+	a []string
+}
+
+var fieldstests = []FieldsTest{
+	{"", []string{}},
+	{" ", []string{}},
+	{" \t ", []string{}},
+	{"  abc  ", []string{"abc"}},
+	{"1 2 3 4", []string{"1", "2", "3", "4"}},
+	{"1  2  3  4", []string{"1", "2", "3", "4"}},
+	{"1\t\t2\t\t3\t4", []string{"1", "2", "3", "4"}},
+	{"1\u20002\u20013\u20024", []string{"1", "2", "3", "4"}},
+	{"\u2000\u2001\u2002", []string{}},
+	{"\n™\t™\n", []string{"™", "™"}},
+	{faces, []string{faces}},
+}
+
+func TestFields(t *testing.T) {
+	for _, tt := range fieldstests {
+		a := Fields(tt.s)
+		if !eq(a, tt.a) {
+			t.Errorf("Fields(%q) = %v; want %v", tt.s, a, tt.a)
+			continue
+		}
+	}
+}
+
+var FieldsFuncTests = []FieldsTest{
+	{"", []string{}},
+	{"XX", []string{}},
+	{"XXhiXXX", []string{"hi"}},
+	{"aXXbXXXcX", []string{"a", "b", "c"}},
+}
+
+func TestFieldsFunc(t *testing.T) {
+	for _, tt := range fieldstests {
+		a := FieldsFunc(tt.s, unicode.IsSpace)
+		if !eq(a, tt.a) {
+			t.Errorf("FieldsFunc(%q, unicode.IsSpace) = %v; want %v", tt.s, a, tt.a)
+			continue
+		}
+	}
+	pred := func(c rune) bool { return c == 'X' }
+	for _, tt := range FieldsFuncTests {
+		a := FieldsFunc(tt.s, pred)
+		if !eq(a, tt.a) {
+			t.Errorf("FieldsFunc(%q) = %v, want %v", tt.s, a, tt.a)
+		}
+	}
+}
+
+// Test case for any function which accepts and returns a single string.
+type StringTest struct {
+	in, out string
+}
+
+// Execute f on each test case.  funcName should be the name of f; it's used
+// in failure reports.
+func runStringTests(t *testing.T, f func(string) string, funcName string, testCases []StringTest) {
+	for _, tc := range testCases {
+		actual := f(tc.in)
+		if actual != tc.out {
+			t.Errorf("%s(%q) = %q; want %q", funcName, tc.in, actual, tc.out)
+		}
+	}
+}
+
+var upperTests = []StringTest{
+	{"", ""},
+	{"abc", "ABC"},
+	{"AbC123", "ABC123"},
+	{"azAZ09_", "AZAZ09_"},
+	{"\u0250\u0250\u0250\u0250\u0250", "\u2C6F\u2C6F\u2C6F\u2C6F\u2C6F"}, // grows one byte per char
+}
+
+var lowerTests = []StringTest{
+	{"", ""},
+	{"abc", "abc"},
+	{"AbC123", "abc123"},
+	{"azAZ09_", "azaz09_"},
+	{"\u2C6D\u2C6D\u2C6D\u2C6D\u2C6D", "\u0251\u0251\u0251\u0251\u0251"}, // shrinks one byte per char
+}
+
+const space = "\t\v\r\f\n\u0085\u00a0\u2000\u3000"
+
+var trimSpaceTests = []StringTest{
+	{"", ""},
+	{"abc", "abc"},
+	{space + "abc" + space, "abc"},
+	{" ", ""},
+	{" \t\r\n \t\t\r\r\n\n ", ""},
+	{" \t\r\n x\t\t\r\r\n\n ", "x"},
+	{" \u2000\t\r\n x\t\t\r\r\ny\n \u3000", "x\t\t\r\r\ny"},
+	{"1 \t\r\n2", "1 \t\r\n2"},
+	{" x\x80", "x\x80"},
+	{" x\xc0", "x\xc0"},
+	{"x \xc0\xc0 ", "x \xc0\xc0"},
+	{"x \xc0", "x \xc0"},
+	{"x \xc0 ", "x \xc0"},
+	{"x \xc0\xc0 ", "x \xc0\xc0"},
+	{"x ☺\xc0\xc0 ", "x ☺\xc0\xc0"},
+	{"x ☺ ", "x ☺"},
+}
+
+func tenRunes(ch rune) string {
+	r := make([]rune, 10)
+	for i := range r {
+		r[i] = ch
+	}
+	return string(r)
+}
+
+// User-defined self-inverse mapping function
+func rot13(r rune) rune {
+	step := rune(13)
+	if r >= 'a' && r <= 'z' {
+		return ((r - 'a' + step) % 26) + 'a'
+	}
+	if r >= 'A' && r <= 'Z' {
+		return ((r - 'A' + step) % 26) + 'A'
+	}
+	return r
+}
+
+func TestMap(t *testing.T) {
+	// Run a couple of awful growth/shrinkage tests
+	a := tenRunes('a')
+	// 1.  Grow.  This triggers two reallocations in Map.
+	maxRune := func(rune) rune { return unicode.MaxRune }
+	m := Map(maxRune, a)
+	expect := tenRunes(unicode.MaxRune)
+	if m != expect {
+		t.Errorf("growing: expected %q got %q", expect, m)
+	}
+
+	// 2. Shrink
+	minRune := func(rune) rune { return 'a' }
+	m = Map(minRune, tenRunes(unicode.MaxRune))
+	expect = a
+	if m != expect {
+		t.Errorf("shrinking: expected %q got %q", expect, m)
+	}
+
+	// 3. Rot13
+	m = Map(rot13, "a to zed")
+	expect = "n gb mrq"
+	if m != expect {
+		t.Errorf("rot13: expected %q got %q", expect, m)
+	}
+
+	// 4. Rot13^2
+	m = Map(rot13, Map(rot13, "a to zed"))
+	expect = "a to zed"
+	if m != expect {
+		t.Errorf("rot13: expected %q got %q", expect, m)
+	}
+
+	// 5. Drop
+	dropNotLatin := func(r rune) rune {
+		if unicode.Is(unicode.Latin, r) {
+			return r
+		}
+		return -1
+	}
+	m = Map(dropNotLatin, "Hello, 세계")
+	expect = "Hello"
+	if m != expect {
+		t.Errorf("drop: expected %q got %q", expect, m)
+	}
+
+	// 6. Identity
+	identity := func(r rune) rune {
+		return r
+	}
+	orig := "Input string that we expect not to be copied."
+	m = Map(identity, orig)
+	if (*reflect.StringHeader)(unsafe.Pointer(&orig)).Data !=
+		(*reflect.StringHeader)(unsafe.Pointer(&m)).Data {
+		t.Error("unexpected copy during identity map")
+	}
+}
+
+func TestToUpper(t *testing.T) { runStringTests(t, ToUpper, "ToUpper", upperTests) }
+
+func TestToLower(t *testing.T) { runStringTests(t, ToLower, "ToLower", lowerTests) }
+
+func BenchmarkMapNoChanges(b *testing.B) {
+	identity := func(r rune) rune {
+		return r
+	}
+	for i := 0; i < b.N; i++ {
+		Map(identity, "Some string that won't be modified.")
+	}
+}
+
+func TestSpecialCase(t *testing.T) {
+	lower := "abcçdefgğhıijklmnoöprsştuüvyz"
+	upper := "ABCÇDEFGĞHIİJKLMNOÖPRSŞTUÜVYZ"
+	u := ToUpperSpecial(unicode.TurkishCase, upper)
+	if u != upper {
+		t.Errorf("Upper(upper) is %s not %s", u, upper)
+	}
+	u = ToUpperSpecial(unicode.TurkishCase, lower)
+	if u != upper {
+		t.Errorf("Upper(lower) is %s not %s", u, upper)
+	}
+	l := ToLowerSpecial(unicode.TurkishCase, lower)
+	if l != lower {
+		t.Errorf("Lower(lower) is %s not %s", l, lower)
+	}
+	l = ToLowerSpecial(unicode.TurkishCase, upper)
+	if l != lower {
+		t.Errorf("Lower(upper) is %s not %s", l, lower)
+	}
+}
+
+func TestTrimSpace(t *testing.T) { runStringTests(t, TrimSpace, "TrimSpace", trimSpaceTests) }
+
+var trimTests = []struct {
+	f            string
+	in, arg, out string
+}{
+	{"Trim", "abba", "a", "bb"},
+	{"Trim", "abba", "ab", ""},
+	{"TrimLeft", "abba", "ab", ""},
+	{"TrimRight", "abba", "ab", ""},
+	{"TrimLeft", "abba", "a", "bba"},
+	{"TrimRight", "abba", "a", "abb"},
+	{"Trim", "<tag>", "<>", "tag"},
+	{"Trim", "* listitem", " *", "listitem"},
+	{"Trim", `"quote"`, `"`, "quote"},
+	{"Trim", "\u2C6F\u2C6F\u0250\u0250\u2C6F\u2C6F", "\u2C6F", "\u0250\u0250"},
+	//empty string tests
+	{"Trim", "abba", "", "abba"},
+	{"Trim", "", "123", ""},
+	{"Trim", "", "", ""},
+	{"TrimLeft", "abba", "", "abba"},
+	{"TrimLeft", "", "123", ""},
+	{"TrimLeft", "", "", ""},
+	{"TrimRight", "abba", "", "abba"},
+	{"TrimRight", "", "123", ""},
+	{"TrimRight", "", "", ""},
+	{"TrimRight", "☺\xc0", "☺", "☺\xc0"},
+	{"TrimPrefix", "aabb", "a", "abb"},
+	{"TrimPrefix", "aabb", "b", "aabb"},
+	{"TrimSuffix", "aabb", "a", "aabb"},
+	{"TrimSuffix", "aabb", "b", "aab"},
+}
+
+func TestTrim(t *testing.T) {
+	for _, tc := range trimTests {
+		name := tc.f
+		var f func(string, string) string
+		switch name {
+		case "Trim":
+			f = Trim
+		case "TrimLeft":
+			f = TrimLeft
+		case "TrimRight":
+			f = TrimRight
+		case "TrimPrefix":
+			f = TrimPrefix
+		case "TrimSuffix":
+			f = TrimSuffix
+		default:
+			t.Errorf("Undefined trim function %s", name)
+		}
+		actual := f(tc.in, tc.arg)
+		if actual != tc.out {
+			t.Errorf("%s(%q, %q) = %q; want %q", name, tc.in, tc.arg, actual, tc.out)
+		}
+	}
+}
+
+type predicate struct {
+	f    func(rune) bool
+	name string
+}
+
+var isSpace = predicate{unicode.IsSpace, "IsSpace"}
+var isDigit = predicate{unicode.IsDigit, "IsDigit"}
+var isUpper = predicate{unicode.IsUpper, "IsUpper"}
+var isValidRune = predicate{
+	func(r rune) bool {
+		return r != utf8.RuneError
+	},
+	"IsValidRune",
+}
+
+func not(p predicate) predicate {
+	return predicate{
+		func(r rune) bool {
+			return !p.f(r)
+		},
+		"not " + p.name,
+	}
+}
+
+var trimFuncTests = []struct {
+	f       predicate
+	in, out string
+}{
+	{isSpace, space + " hello " + space, "hello"},
+	{isDigit, "\u0e50\u0e5212hello34\u0e50\u0e51", "hello"},
+	{isUpper, "\u2C6F\u2C6F\u2C6F\u2C6FABCDhelloEF\u2C6F\u2C6FGH\u2C6F\u2C6F", "hello"},
+	{not(isSpace), "hello" + space + "hello", space},
+	{not(isDigit), "hello\u0e50\u0e521234\u0e50\u0e51helo", "\u0e50\u0e521234\u0e50\u0e51"},
+	{isValidRune, "ab\xc0a\xc0cd", "\xc0a\xc0"},
+	{not(isValidRune), "\xc0a\xc0", "a"},
+}
+
+func TestTrimFunc(t *testing.T) {
+	for _, tc := range trimFuncTests {
+		actual := TrimFunc(tc.in, tc.f.f)
+		if actual != tc.out {
+			t.Errorf("TrimFunc(%q, %q) = %q; want %q", tc.in, tc.f.name, actual, tc.out)
+		}
+	}
+}
+
+var indexFuncTests = []struct {
+	in          string
+	f           predicate
+	first, last int
+}{
+	{"", isValidRune, -1, -1},
+	{"abc", isDigit, -1, -1},
+	{"0123", isDigit, 0, 3},
+	{"a1b", isDigit, 1, 1},
+	{space, isSpace, 0, len(space) - 3}, // last rune in space is 3 bytes
+	{"\u0e50\u0e5212hello34\u0e50\u0e51", isDigit, 0, 18},
+	{"\u2C6F\u2C6F\u2C6F\u2C6FABCDhelloEF\u2C6F\u2C6FGH\u2C6F\u2C6F", isUpper, 0, 34},
+	{"12\u0e50\u0e52hello34\u0e50\u0e51", not(isDigit), 8, 12},
+
+	// tests of invalid UTF-8
+	{"\x801", isDigit, 1, 1},
+	{"\x80abc", isDigit, -1, -1},
+	{"\xc0a\xc0", isValidRune, 1, 1},
+	{"\xc0a\xc0", not(isValidRune), 0, 2},
+	{"\xc0☺\xc0", not(isValidRune), 0, 4},
+	{"\xc0☺\xc0\xc0", not(isValidRune), 0, 5},
+	{"ab\xc0a\xc0cd", not(isValidRune), 2, 4},
+	{"a\xe0\x80cd", not(isValidRune), 1, 2},
+	{"\x80\x80\x80\x80", not(isValidRune), 0, 3},
+}
+
+func TestIndexFunc(t *testing.T) {
+	for _, tc := range indexFuncTests {
+		first := IndexFunc(tc.in, tc.f.f)
+		if first != tc.first {
+			t.Errorf("IndexFunc(%q, %s) = %d; want %d", tc.in, tc.f.name, first, tc.first)
+		}
+		last := LastIndexFunc(tc.in, tc.f.f)
+		if last != tc.last {
+			t.Errorf("LastIndexFunc(%q, %s) = %d; want %d", tc.in, tc.f.name, last, tc.last)
+		}
+	}
+}
+
+func equal(m string, s1, s2 string, t *testing.T) bool {
+	if s1 == s2 {
+		return true
+	}
+	e1 := Split(s1, "")
+	e2 := Split(s2, "")
+	for i, c1 := range e1 {
+		if i >= len(e2) {
+			break
+		}
+		r1, _ := utf8.DecodeRuneInString(c1)
+		r2, _ := utf8.DecodeRuneInString(e2[i])
+		if r1 != r2 {
+			t.Errorf("%s diff at %d: U+%04X U+%04X", m, i, r1, r2)
+		}
+	}
+	return false
+}
+
+func TestCaseConsistency(t *testing.T) {
+	// Make a string of all the runes.
+	numRunes := int(unicode.MaxRune + 1)
+	if testing.Short() {
+		numRunes = 1000
+	}
+	a := make([]rune, numRunes)
+	for i := range a {
+		a[i] = rune(i)
+	}
+	s := string(a)
+	// convert the cases.
+	upper := ToUpper(s)
+	lower := ToLower(s)
+
+	// Consistency checks
+	if n := utf8.RuneCountInString(upper); n != numRunes {
+		t.Error("rune count wrong in upper:", n)
+	}
+	if n := utf8.RuneCountInString(lower); n != numRunes {
+		t.Error("rune count wrong in lower:", n)
+	}
+	if !equal("ToUpper(upper)", ToUpper(upper), upper, t) {
+		t.Error("ToUpper(upper) consistency fail")
+	}
+	if !equal("ToLower(lower)", ToLower(lower), lower, t) {
+		t.Error("ToLower(lower) consistency fail")
+	}
+	/*
+		  These fail because of non-one-to-oneness of the data, such as multiple
+		  upper case 'I' mapping to 'i'.  We comment them out but keep them for
+		  interest.
+		  For instance: CAPITAL LETTER I WITH DOT ABOVE:
+			unicode.ToUpper(unicode.ToLower('\u0130')) != '\u0130'
+
+		if !equal("ToUpper(lower)", ToUpper(lower), upper, t) {
+			t.Error("ToUpper(lower) consistency fail");
+		}
+		if !equal("ToLower(upper)", ToLower(upper), lower, t) {
+			t.Error("ToLower(upper) consistency fail");
+		}
+	*/
+}
+
+var RepeatTests = []struct {
+	in, out string
+	count   int
+}{
+	{"", "", 0},
+	{"", "", 1},
+	{"", "", 2},
+	{"-", "", 0},
+	{"-", "-", 1},
+	{"-", "----------", 10},
+	{"abc ", "abc abc abc ", 3},
+}
+
+func TestRepeat(t *testing.T) {
+	for _, tt := range RepeatTests {
+		a := Repeat(tt.in, tt.count)
+		if !equal("Repeat(s)", a, tt.out, t) {
+			t.Errorf("Repeat(%v, %d) = %v; want %v", tt.in, tt.count, a, tt.out)
+			continue
+		}
+	}
+}
+
+func runesEqual(a, b []rune) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, r := range a {
+		if r != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+var RunesTests = []struct {
+	in    string
+	out   []rune
+	lossy bool
+}{
+	{"", []rune{}, false},
+	{" ", []rune{32}, false},
+	{"ABC", []rune{65, 66, 67}, false},
+	{"abc", []rune{97, 98, 99}, false},
+	{"\u65e5\u672c\u8a9e", []rune{26085, 26412, 35486}, false},
+	{"ab\x80c", []rune{97, 98, 0xFFFD, 99}, true},
+	{"ab\xc0c", []rune{97, 98, 0xFFFD, 99}, true},
+}
+
+func TestRunes(t *testing.T) {
+	for _, tt := range RunesTests {
+		a := []rune(tt.in)
+		if !runesEqual(a, tt.out) {
+			t.Errorf("[]rune(%q) = %v; want %v", tt.in, a, tt.out)
+			continue
+		}
+		if !tt.lossy {
+			// can only test reassembly if we didn't lose information
+			s := string(a)
+			if s != tt.in {
+				t.Errorf("string([]rune(%q)) = %x; want %x", tt.in, s, tt.in)
+			}
+		}
+	}
+}
+
+func TestReadByte(t *testing.T) {
+	testStrings := []string{"", abcd, faces, commas}
+	for _, s := range testStrings {
+		reader := NewReader(s)
+		if e := reader.UnreadByte(); e == nil {
+			t.Errorf("Unreading %q at beginning: expected error", s)
+		}
+		var res bytes.Buffer
+		for {
+			b, e := reader.ReadByte()
+			if e == io.EOF {
+				break
+			}
+			if e != nil {
+				t.Errorf("Reading %q: %s", s, e)
+				break
+			}
+			res.WriteByte(b)
+			// unread and read again
+			e = reader.UnreadByte()
+			if e != nil {
+				t.Errorf("Unreading %q: %s", s, e)
+				break
+			}
+			b1, e := reader.ReadByte()
+			if e != nil {
+				t.Errorf("Reading %q after unreading: %s", s, e)
+				break
+			}
+			if b1 != b {
+				t.Errorf("Reading %q after unreading: want byte %q, got %q", s, b, b1)
+				break
+			}
+		}
+		if res.String() != s {
+			t.Errorf("Reader(%q).ReadByte() produced %q", s, res.String())
+		}
+	}
+}
+
+func TestReadRune(t *testing.T) {
+	testStrings := []string{"", abcd, faces, commas}
+	for _, s := range testStrings {
+		reader := NewReader(s)
+		if e := reader.UnreadRune(); e == nil {
+			t.Errorf("Unreading %q at beginning: expected error", s)
+		}
+		res := ""
+		for {
+			r, z, e := reader.ReadRune()
+			if e == io.EOF {
+				break
+			}
+			if e != nil {
+				t.Errorf("Reading %q: %s", s, e)
+				break
+			}
+			res += string(r)
+			// unread and read again
+			e = reader.UnreadRune()
+			if e != nil {
+				t.Errorf("Unreading %q: %s", s, e)
+				break
+			}
+			r1, z1, e := reader.ReadRune()
+			if e != nil {
+				t.Errorf("Reading %q after unreading: %s", s, e)
+				break
+			}
+			if r1 != r {
+				t.Errorf("Reading %q after unreading: want rune %q, got %q", s, r, r1)
+				break
+			}
+			if z1 != z {
+				t.Errorf("Reading %q after unreading: want size %d, got %d", s, z, z1)
+				break
+			}
+		}
+		if res != s {
+			t.Errorf("Reader(%q).ReadRune() produced %q", s, res)
+		}
+	}
+}
+
+var UnreadRuneErrorTests = []struct {
+	name string
+	f    func(*Reader)
+}{
+	{"Read", func(r *Reader) { r.Read([]byte{0}) }},
+	{"ReadByte", func(r *Reader) { r.ReadByte() }},
+	{"UnreadRune", func(r *Reader) { r.UnreadRune() }},
+	{"Seek", func(r *Reader) { r.Seek(0, 1) }},
+	{"WriteTo", func(r *Reader) { r.WriteTo(&bytes.Buffer{}) }},
+}
+
+func TestUnreadRuneError(t *testing.T) {
+	for _, tt := range UnreadRuneErrorTests {
+		reader := NewReader("0123456789")
+		if _, _, err := reader.ReadRune(); err != nil {
+			// should not happen
+			t.Fatal(err)
+		}
+		tt.f(reader)
+		err := reader.UnreadRune()
+		if err == nil {
+			t.Errorf("Unreading after %s: expected error", tt.name)
+		}
+	}
+}
+
+var ReplaceTests = []struct {
+	in       string
+	old, new string
+	n        int
+	out      string
+}{
+	{"hello", "l", "L", 0, "hello"},
+	{"hello", "l", "L", -1, "heLLo"},
+	{"hello", "x", "X", -1, "hello"},
+	{"", "x", "X", -1, ""},
+	{"radar", "r", "<r>", -1, "<r>ada<r>"},
+	{"", "", "<>", -1, "<>"},
+	{"banana", "a", "<>", -1, "b<>n<>n<>"},
+	{"banana", "a", "<>", 1, "b<>nana"},
+	{"banana", "a", "<>", 1000, "b<>n<>n<>"},
+	{"banana", "an", "<>", -1, "b<><>a"},
+	{"banana", "ana", "<>", -1, "b<>na"},
+	{"banana", "", "<>", -1, "<>b<>a<>n<>a<>n<>a<>"},
+	{"banana", "", "<>", 10, "<>b<>a<>n<>a<>n<>a<>"},
+	{"banana", "", "<>", 6, "<>b<>a<>n<>a<>n<>a"},
+	{"banana", "", "<>", 5, "<>b<>a<>n<>a<>na"},
+	{"banana", "", "<>", 1, "<>banana"},
+	{"banana", "a", "a", -1, "banana"},
+	{"banana", "a", "a", 1, "banana"},
+	{"☺☻☹", "", "<>", -1, "<>☺<>☻<>☹<>"},
+}
+
+func TestReplace(t *testing.T) {
+	for _, tt := range ReplaceTests {
+		if s := Replace(tt.in, tt.old, tt.new, tt.n); s != tt.out {
+			t.Errorf("Replace(%q, %q, %q, %d) = %q, want %q", tt.in, tt.old, tt.new, tt.n, s, tt.out)
+		}
+	}
+}
+
+var TitleTests = []struct {
+	in, out string
+}{
+	{"", ""},
+	{"a", "A"},
+	{" aaa aaa aaa ", " Aaa Aaa Aaa "},
+	{" Aaa Aaa Aaa ", " Aaa Aaa Aaa "},
+	{"123a456", "123a456"},
+	{"double-blind", "Double-Blind"},
+	{"ÿøû", "Ÿøû"},
+	{"with_underscore", "With_underscore"},
+	{"unicode \xe2\x80\xa8 line separator", "Unicode \xe2\x80\xa8 Line Separator"},
+}
+
+func TestTitle(t *testing.T) {
+	for _, tt := range TitleTests {
+		if s := Title(tt.in); s != tt.out {
+			t.Errorf("Title(%q) = %q, want %q", tt.in, s, tt.out)
+		}
+	}
+}
+
+var ContainsTests = []struct {
+	str, substr string
+	expected    bool
+}{
+	{"abc", "bc", true},
+	{"abc", "bcd", false},
+	{"abc", "", true},
+	{"", "a", false},
+}
+
+func TestContains(t *testing.T) {
+	for _, ct := range ContainsTests {
+		if Contains(ct.str, ct.substr) != ct.expected {
+			t.Errorf("Contains(%s, %s) = %v, want %v",
+				ct.str, ct.substr, !ct.expected, ct.expected)
+		}
+	}
+}
+
+var ContainsAnyTests = []struct {
+	str, substr string
+	expected    bool
+}{
+	{"", "", false},
+	{"", "a", false},
+	{"", "abc", false},
+	{"a", "", false},
+	{"a", "a", true},
+	{"aaa", "a", true},
+	{"abc", "xyz", false},
+	{"abc", "xcz", true},
+	{"a☺b☻c☹d", "uvw☻xyz", true},
+	{"aRegExp*", ".(|)*+?^$[]", true},
+	{dots + dots + dots, " ", false},
+}
+
+func TestContainsAny(t *testing.T) {
+	for _, ct := range ContainsAnyTests {
+		if ContainsAny(ct.str, ct.substr) != ct.expected {
+			t.Errorf("ContainsAny(%s, %s) = %v, want %v",
+				ct.str, ct.substr, !ct.expected, ct.expected)
+		}
+	}
+}
+
+var ContainsRuneTests = []struct {
+	str      string
+	r        rune
+	expected bool
+}{
+	{"", 'a', false},
+	{"a", 'a', true},
+	{"aaa", 'a', true},
+	{"abc", 'y', false},
+	{"abc", 'c', true},
+	{"a☺b☻c☹d", 'x', false},
+	{"a☺b☻c☹d", '☻', true},
+	{"aRegExp*", '*', true},
+}
+
+func TestContainsRune(t *testing.T) {
+	for _, ct := range ContainsRuneTests {
+		if ContainsRune(ct.str, ct.r) != ct.expected {
+			t.Errorf("ContainsRune(%q, %q) = %v, want %v",
+				ct.str, ct.r, !ct.expected, ct.expected)
+		}
+	}
+}
+
+var EqualFoldTests = []struct {
+	s, t string
+	out  bool
+}{
+	{"abc", "abc", true},
+	{"ABcd", "ABcd", true},
+	{"123abc", "123ABC", true},
+	{"αβδ", "ΑΒΔ", true},
+	{"abc", "xyz", false},
+	{"abc", "XYZ", false},
+	{"abcdefghijk", "abcdefghijX", false},
+	{"abcdefghijk", "abcdefghij\u212A", true},
+	{"abcdefghijK", "abcdefghij\u212A", true},
+	{"abcdefghijkz", "abcdefghij\u212Ay", false},
+	{"abcdefghijKz", "abcdefghij\u212Ay", false},
+}
+
+func TestEqualFold(t *testing.T) {
+	for _, tt := range EqualFoldTests {
+		if out := EqualFold(tt.s, tt.t); out != tt.out {
+			t.Errorf("EqualFold(%#q, %#q) = %v, want %v", tt.s, tt.t, out, tt.out)
+		}
+		if out := EqualFold(tt.t, tt.s); out != tt.out {
+			t.Errorf("EqualFold(%#q, %#q) = %v, want %v", tt.t, tt.s, out, tt.out)
+		}
+	}
+}
+
+var CountTests = []struct {
+	s, sep string
+	num    int
+}{
+	{"", "", 1},
+	{"", "notempty", 0},
+	{"notempty", "", 9},
+	{"smaller", "not smaller", 0},
+	{"12345678987654321", "6", 2},
+	{"611161116", "6", 3},
+	{"notequal", "NotEqual", 0},
+	{"equal", "equal", 1},
+	{"abc1231231123q", "123", 3},
+	{"11111", "11", 2},
+}
+
+func TestCount(t *testing.T) {
+	for _, tt := range CountTests {
+		if num := Count(tt.s, tt.sep); num != tt.num {
+			t.Errorf("Count(\"%s\", \"%s\") = %d, want %d", tt.s, tt.sep, num, tt.num)
+		}
+	}
+}
+
+func makeBenchInputHard() string {
+	tokens := [...]string{
+		"<a>", "<p>", "<b>", "<strong>",
+		"</a>", "</p>", "</b>", "</strong>",
+		"hello", "world",
+	}
+	x := make([]byte, 0, 1<<20)
+	for {
+		i := rand.Intn(len(tokens))
+		if len(x)+len(tokens[i]) >= 1<<20 {
+			break
+		}
+		x = append(x, tokens[i]...)
+	}
+	return string(x)
+}
+
+var benchInputHard = makeBenchInputHard()
+
+func benchmarkIndexHard(b *testing.B, sep string) {
+	for i := 0; i < b.N; i++ {
+		Index(benchInputHard, sep)
+	}
+}
+
+func benchmarkLastIndexHard(b *testing.B, sep string) {
+	for i := 0; i < b.N; i++ {
+		LastIndex(benchInputHard, sep)
+	}
+}
+
+func benchmarkCountHard(b *testing.B, sep string) {
+	for i := 0; i < b.N; i++ {
+		Count(benchInputHard, sep)
+	}
+}
+
+func BenchmarkIndexHard1(b *testing.B) { benchmarkIndexHard(b, "<>") }
+func BenchmarkIndexHard2(b *testing.B) { benchmarkIndexHard(b, "</pre>") }
+func BenchmarkIndexHard3(b *testing.B) { benchmarkIndexHard(b, "<b>hello world</b>") }
+
+func BenchmarkLastIndexHard1(b *testing.B) { benchmarkLastIndexHard(b, "<>") }
+func BenchmarkLastIndexHard2(b *testing.B) { benchmarkLastIndexHard(b, "</pre>") }
+func BenchmarkLastIndexHard3(b *testing.B) { benchmarkLastIndexHard(b, "<b>hello world</b>") }
+
+func BenchmarkCountHard1(b *testing.B) { benchmarkCountHard(b, "<>") }
+func BenchmarkCountHard2(b *testing.B) { benchmarkCountHard(b, "</pre>") }
+func BenchmarkCountHard3(b *testing.B) { benchmarkCountHard(b, "<b>hello world</b>") }
+
+var benchInputTorture = Repeat("ABC", 1<<10) + "123" + Repeat("ABC", 1<<10)
+var benchNeedleTorture = Repeat("ABC", 1<<10+1)
+
+func BenchmarkIndexTorture(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Index(benchInputTorture, benchNeedleTorture)
+	}
+}
+
+func BenchmarkCountTorture(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Count(benchInputTorture, benchNeedleTorture)
+	}
+}
+
+func BenchmarkCountTortureOverlapping(b *testing.B) {
+	A := Repeat("ABC", 1<<20)
+	B := Repeat("ABC", 1<<10)
+	for i := 0; i < b.N; i++ {
+		Count(A, B)
+	}
+}
+
+var makeFieldsInput = func() string {
+	x := make([]byte, 1<<20)
+	// Input is ~10% space, ~10% 2-byte UTF-8, rest ASCII non-space.
+	for i := range x {
+		switch rand.Intn(10) {
+		case 0:
+			x[i] = ' '
+		case 1:
+			if i > 0 && x[i-1] == 'x' {
+				copy(x[i-1:], "χ")
+				break
+			}
+			fallthrough
+		default:
+			x[i] = 'x'
+		}
+	}
+	return string(x)
+}
+
+var fieldsInput = makeFieldsInput()
+
+func BenchmarkFields(b *testing.B) {
+	b.SetBytes(int64(len(fieldsInput)))
+	for i := 0; i < b.N; i++ {
+		Fields(fieldsInput)
+	}
+}
+
+func BenchmarkFieldsFunc(b *testing.B) {
+	b.SetBytes(int64(len(fieldsInput)))
+	for i := 0; i < b.N; i++ {
+		FieldsFunc(fieldsInput, unicode.IsSpace)
+	}
+}
+
+func BenchmarkSplit1(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Split(benchInputHard, "")
+	}
+}
+
+func BenchmarkSplit2(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Split(benchInputHard, "/")
+	}
+}
+
+func BenchmarkSplit3(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Split(benchInputHard, "hello")
+	}
+}
+
+func BenchmarkRepeat(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Repeat("-", 80)
+	}
+}