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.

7 files changed, 1314 insertions, 0 deletions

diff --git a/src/compress/bzip2/bit_reader.go b/src/compress/bzip2/bit_reader.go
new file mode 100644
index 000000000..32d1036ae
--- /dev/null
+++ b/src/compress/bzip2/bit_reader.go
@@ -0,0 +1,90 @@
+// 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 bzip2
+
+import (
+	"bufio"
+	"io"
+)
+
+// bitReader wraps an io.Reader and provides the ability to read values,
+// bit-by-bit, from it. Its Read* methods don't return the usual error
+// because the error handling was verbose. Instead, any error is kept and can
+// be checked afterwards.
+type bitReader struct {
+	r    io.ByteReader
+	n    uint64
+	bits uint
+	err  error
+}
+
+// newBitReader returns a new bitReader reading from r. If r is not
+// already an io.ByteReader, it will be converted via a bufio.Reader.
+func newBitReader(r io.Reader) bitReader {
+	byter, ok := r.(io.ByteReader)
+	if !ok {
+		byter = bufio.NewReader(r)
+	}
+	return bitReader{r: byter}
+}
+
+// ReadBits64 reads the given number of bits and returns them in the
+// least-significant part of a uint64. In the event of an error, it returns 0
+// and the error can be obtained by calling Err().
+func (br *bitReader) ReadBits64(bits uint) (n uint64) {
+	for bits > br.bits {
+		b, err := br.r.ReadByte()
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		if err != nil {
+			br.err = err
+			return 0
+		}
+		br.n <<= 8
+		br.n |= uint64(b)
+		br.bits += 8
+	}
+
+	// br.n looks like this (assuming that br.bits = 14 and bits = 6):
+	// Bit: 111111
+	//      5432109876543210
+	//
+	//         (6 bits, the desired output)
+	//        |-----|
+	//        V     V
+	//      0101101101001110
+	//        ^            ^
+	//        |------------|
+	//           br.bits (num valid bits)
+	//
+	// This the next line right shifts the desired bits into the
+	// least-significant places and masks off anything above.
+	n = (br.n >> (br.bits - bits)) & ((1 << bits) - 1)
+	br.bits -= bits
+	return
+}
+
+func (br *bitReader) ReadBits(bits uint) (n int) {
+	n64 := br.ReadBits64(bits)
+	return int(n64)
+}
+
+func (br *bitReader) ReadBit() bool {
+	n := br.ReadBits(1)
+	return n != 0
+}
+
+func (br *bitReader) TryReadBit() (bit byte, ok bool) {
+	if br.bits > 0 {
+		br.bits--
+		return byte(br.n>>br.bits) & 1, true
+	}
+	return 0, false
+}
+
+func (br *bitReader) Err() error {
+	return br.err
+}
diff --git a/src/compress/bzip2/bzip2.go b/src/compress/bzip2/bzip2.go
new file mode 100644
index 000000000..d318116a1
--- /dev/null
+++ b/src/compress/bzip2/bzip2.go
@@ -0,0 +1,501 @@
+// 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 bzip2 implements bzip2 decompression.
+package bzip2
+
+import "io"
+
+// There's no RFC for bzip2. I used the Wikipedia page for reference and a lot
+// of guessing: http://en.wikipedia.org/wiki/Bzip2
+// The source code to pyflate was useful for debugging:
+// http://www.paul.sladen.org/projects/pyflate
+
+// A StructuralError is returned when the bzip2 data is found to be
+// syntactically invalid.
+type StructuralError string
+
+func (s StructuralError) Error() string {
+	return "bzip2 data invalid: " + string(s)
+}
+
+// A reader decompresses bzip2 compressed data.
+type reader struct {
+	br           bitReader
+	fileCRC      uint32
+	blockCRC     uint32
+	wantBlockCRC uint32
+	setupDone    bool // true if we have parsed the bzip2 header.
+	blockSize    int  // blockSize in bytes, i.e. 900 * 1024.
+	eof          bool
+	buf          []byte    // stores Burrows-Wheeler transformed data.
+	c            [256]uint // the `C' array for the inverse BWT.
+	tt           []uint32  // mirrors the `tt' array in the bzip2 source and contains the P array in the upper 24 bits.
+	tPos         uint32    // Index of the next output byte in tt.
+
+	preRLE      []uint32 // contains the RLE data still to be processed.
+	preRLEUsed  int      // number of entries of preRLE used.
+	lastByte    int      // the last byte value seen.
+	byteRepeats uint     // the number of repeats of lastByte seen.
+	repeats     uint     // the number of copies of lastByte to output.
+}
+
+// NewReader returns an io.Reader which decompresses bzip2 data from r.
+func NewReader(r io.Reader) io.Reader {
+	bz2 := new(reader)
+	bz2.br = newBitReader(r)
+	return bz2
+}
+
+const bzip2FileMagic = 0x425a // "BZ"
+const bzip2BlockMagic = 0x314159265359
+const bzip2FinalMagic = 0x177245385090
+
+// setup parses the bzip2 header.
+func (bz2 *reader) setup(needMagic bool) error {
+	br := &bz2.br
+
+	if needMagic {
+		magic := br.ReadBits(16)
+		if magic != bzip2FileMagic {
+			return StructuralError("bad magic value")
+		}
+	}
+
+	t := br.ReadBits(8)
+	if t != 'h' {
+		return StructuralError("non-Huffman entropy encoding")
+	}
+
+	level := br.ReadBits(8)
+	if level < '1' || level > '9' {
+		return StructuralError("invalid compression level")
+	}
+
+	bz2.fileCRC = 0
+	bz2.blockSize = 100 * 1024 * (int(level) - '0')
+	if bz2.blockSize > len(bz2.tt) {
+		bz2.tt = make([]uint32, bz2.blockSize)
+	}
+	return nil
+}
+
+func (bz2 *reader) Read(buf []byte) (n int, err error) {
+	if bz2.eof {
+		return 0, io.EOF
+	}
+
+	if !bz2.setupDone {
+		err = bz2.setup(true)
+		brErr := bz2.br.Err()
+		if brErr != nil {
+			err = brErr
+		}
+		if err != nil {
+			return 0, err
+		}
+		bz2.setupDone = true
+	}
+
+	n, err = bz2.read(buf)
+	brErr := bz2.br.Err()
+	if brErr != nil {
+		err = brErr
+	}
+	return
+}
+
+func (bz2 *reader) readFromBlock(buf []byte) int {
+	// bzip2 is a block based compressor, except that it has a run-length
+	// preprocessing step. The block based nature means that we can
+	// preallocate fixed-size buffers and reuse them. However, the RLE
+	// preprocessing would require allocating huge buffers to store the
+	// maximum expansion. Thus we process blocks all at once, except for
+	// the RLE which we decompress as required.
+	n := 0
+	for (bz2.repeats > 0 || bz2.preRLEUsed < len(bz2.preRLE)) && n < len(buf) {
+		// We have RLE data pending.
+
+		// The run-length encoding works like this:
+		// Any sequence of four equal bytes is followed by a length
+		// byte which contains the number of repeats of that byte to
+		// include. (The number of repeats can be zero.) Because we are
+		// decompressing on-demand our state is kept in the reader
+		// object.
+
+		if bz2.repeats > 0 {
+			buf[n] = byte(bz2.lastByte)
+			n++
+			bz2.repeats--
+			if bz2.repeats == 0 {
+				bz2.lastByte = -1
+			}
+			continue
+		}
+
+		bz2.tPos = bz2.preRLE[bz2.tPos]
+		b := byte(bz2.tPos)
+		bz2.tPos >>= 8
+		bz2.preRLEUsed++
+
+		if bz2.byteRepeats == 3 {
+			bz2.repeats = uint(b)
+			bz2.byteRepeats = 0
+			continue
+		}
+
+		if bz2.lastByte == int(b) {
+			bz2.byteRepeats++
+		} else {
+			bz2.byteRepeats = 0
+		}
+		bz2.lastByte = int(b)
+
+		buf[n] = b
+		n++
+	}
+
+	return n
+}
+
+func (bz2 *reader) read(buf []byte) (int, error) {
+	for {
+		n := bz2.readFromBlock(buf)
+		if n > 0 {
+			bz2.blockCRC = updateCRC(bz2.blockCRC, buf[:n])
+			return n, nil
+		}
+
+		// End of block. Check CRC.
+		if bz2.blockCRC != bz2.wantBlockCRC {
+			bz2.br.err = StructuralError("block checksum mismatch")
+			return 0, bz2.br.err
+		}
+
+		// Find next block.
+		br := &bz2.br
+		switch br.ReadBits64(48) {
+		default:
+			return 0, StructuralError("bad magic value found")
+
+		case bzip2BlockMagic:
+			// Start of block.
+			err := bz2.readBlock()
+			if err != nil {
+				return 0, err
+			}
+
+		case bzip2FinalMagic:
+			// Check end-of-file CRC.
+			wantFileCRC := uint32(br.ReadBits64(32))
+			if br.err != nil {
+				return 0, br.err
+			}
+			if bz2.fileCRC != wantFileCRC {
+				br.err = StructuralError("file checksum mismatch")
+				return 0, br.err
+			}
+
+			// Skip ahead to byte boundary.
+			// Is there a file concatenated to this one?
+			// It would start with BZ.
+			if br.bits%8 != 0 {
+				br.ReadBits(br.bits % 8)
+			}
+			b, err := br.r.ReadByte()
+			if err == io.EOF {
+				br.err = io.EOF
+				bz2.eof = true
+				return 0, io.EOF
+			}
+			if err != nil {
+				br.err = err
+				return 0, err
+			}
+			z, err := br.r.ReadByte()
+			if err != nil {
+				if err == io.EOF {
+					err = io.ErrUnexpectedEOF
+				}
+				br.err = err
+				return 0, err
+			}
+			if b != 'B' || z != 'Z' {
+				return 0, StructuralError("bad magic value in continuation file")
+			}
+			if err := bz2.setup(false); err != nil {
+				return 0, err
+			}
+		}
+	}
+}
+
+// readBlock reads a bzip2 block. The magic number should already have been consumed.
+func (bz2 *reader) readBlock() (err error) {
+	br := &bz2.br
+	bz2.wantBlockCRC = uint32(br.ReadBits64(32)) // skip checksum. TODO: check it if we can figure out what it is.
+	bz2.blockCRC = 0
+	bz2.fileCRC = (bz2.fileCRC<<1 | bz2.fileCRC>>31) ^ bz2.wantBlockCRC
+	randomized := br.ReadBits(1)
+	if randomized != 0 {
+		return StructuralError("deprecated randomized files")
+	}
+	origPtr := uint(br.ReadBits(24))
+
+	// If not every byte value is used in the block (i.e., it's text) then
+	// the symbol set is reduced. The symbols used are stored as a
+	// two-level, 16x16 bitmap.
+	symbolRangeUsedBitmap := br.ReadBits(16)
+	symbolPresent := make([]bool, 256)
+	numSymbols := 0
+	for symRange := uint(0); symRange < 16; symRange++ {
+		if symbolRangeUsedBitmap&(1<<(15-symRange)) != 0 {
+			bits := br.ReadBits(16)
+			for symbol := uint(0); symbol < 16; symbol++ {
+				if bits&(1<<(15-symbol)) != 0 {
+					symbolPresent[16*symRange+symbol] = true
+					numSymbols++
+				}
+			}
+		}
+	}
+
+	if numSymbols == 0 {
+		// There must be an EOF symbol.
+		return StructuralError("no symbols in input")
+	}
+
+	// A block uses between two and six different Huffman trees.
+	numHuffmanTrees := br.ReadBits(3)
+	if numHuffmanTrees < 2 || numHuffmanTrees > 6 {
+		return StructuralError("invalid number of Huffman trees")
+	}
+
+	// The Huffman tree can switch every 50 symbols so there's a list of
+	// tree indexes telling us which tree to use for each 50 symbol block.
+	numSelectors := br.ReadBits(15)
+	treeIndexes := make([]uint8, numSelectors)
+
+	// The tree indexes are move-to-front transformed and stored as unary
+	// numbers.
+	mtfTreeDecoder := newMTFDecoderWithRange(numHuffmanTrees)
+	for i := range treeIndexes {
+		c := 0
+		for {
+			inc := br.ReadBits(1)
+			if inc == 0 {
+				break
+			}
+			c++
+		}
+		if c >= numHuffmanTrees {
+			return StructuralError("tree index too large")
+		}
+		treeIndexes[i] = uint8(mtfTreeDecoder.Decode(c))
+	}
+
+	// The list of symbols for the move-to-front transform is taken from
+	// the previously decoded symbol bitmap.
+	symbols := make([]byte, numSymbols)
+	nextSymbol := 0
+	for i := 0; i < 256; i++ {
+		if symbolPresent[i] {
+			symbols[nextSymbol] = byte(i)
+			nextSymbol++
+		}
+	}
+	mtf := newMTFDecoder(symbols)
+
+	numSymbols += 2 // to account for RUNA and RUNB symbols
+	huffmanTrees := make([]huffmanTree, numHuffmanTrees)
+
+	// Now we decode the arrays of code-lengths for each tree.
+	lengths := make([]uint8, numSymbols)
+	for i := range huffmanTrees {
+		// The code lengths are delta encoded from a 5-bit base value.
+		length := br.ReadBits(5)
+		for j := range lengths {
+			for {
+				if !br.ReadBit() {
+					break
+				}
+				if br.ReadBit() {
+					length--
+				} else {
+					length++
+				}
+			}
+			if length < 0 || length > 20 {
+				return StructuralError("Huffman length out of range")
+			}
+			lengths[j] = uint8(length)
+		}
+		huffmanTrees[i], err = newHuffmanTree(lengths)
+		if err != nil {
+			return err
+		}
+	}
+
+	selectorIndex := 1 // the next tree index to use
+	if len(treeIndexes) == 0 {
+		return StructuralError("no tree selectors given")
+	}
+	if int(treeIndexes[0]) >= len(huffmanTrees) {
+		return StructuralError("tree selector out of range")
+	}
+	currentHuffmanTree := huffmanTrees[treeIndexes[0]]
+	bufIndex := 0 // indexes bz2.buf, the output buffer.
+	// The output of the move-to-front transform is run-length encoded and
+	// we merge the decoding into the Huffman parsing loop. These two
+	// variables accumulate the repeat count. See the Wikipedia page for
+	// details.
+	repeat := 0
+	repeat_power := 0
+
+	// The `C' array (used by the inverse BWT) needs to be zero initialized.
+	for i := range bz2.c {
+		bz2.c[i] = 0
+	}
+
+	decoded := 0 // counts the number of symbols decoded by the current tree.
+	for {
+		if decoded == 50 {
+			if selectorIndex >= numSelectors {
+				return StructuralError("insufficient selector indices for number of symbols")
+			}
+			if int(treeIndexes[selectorIndex]) >= len(huffmanTrees) {
+				return StructuralError("tree selector out of range")
+			}
+			currentHuffmanTree = huffmanTrees[treeIndexes[selectorIndex]]
+			selectorIndex++
+			decoded = 0
+		}
+
+		v := currentHuffmanTree.Decode(br)
+		decoded++
+
+		if v < 2 {
+			// This is either the RUNA or RUNB symbol.
+			if repeat == 0 {
+				repeat_power = 1
+			}
+			repeat += repeat_power << v
+			repeat_power <<= 1
+
+			// This limit of 2 million comes from the bzip2 source
+			// code. It prevents repeat from overflowing.
+			if repeat > 2*1024*1024 {
+				return StructuralError("repeat count too large")
+			}
+			continue
+		}
+
+		if repeat > 0 {
+			// We have decoded a complete run-length so we need to
+			// replicate the last output symbol.
+			if repeat > bz2.blockSize-bufIndex {
+				return StructuralError("repeats past end of block")
+			}
+			for i := 0; i < repeat; i++ {
+				b := byte(mtf.First())
+				bz2.tt[bufIndex] = uint32(b)
+				bz2.c[b]++
+				bufIndex++
+			}
+			repeat = 0
+		}
+
+		if int(v) == numSymbols-1 {
+			// This is the EOF symbol. Because it's always at the
+			// end of the move-to-front list, and never gets moved
+			// to the front, it has this unique value.
+			break
+		}
+
+		// Since two metasymbols (RUNA and RUNB) have values 0 and 1,
+		// one would expect |v-2| to be passed to the MTF decoder.
+		// However, the front of the MTF list is never referenced as 0,
+		// it's always referenced with a run-length of 1. Thus 0
+		// doesn't need to be encoded and we have |v-1| in the next
+		// line.
+		b := byte(mtf.Decode(int(v - 1)))
+		if bufIndex >= bz2.blockSize {
+			return StructuralError("data exceeds block size")
+		}
+		bz2.tt[bufIndex] = uint32(b)
+		bz2.c[b]++
+		bufIndex++
+	}
+
+	if origPtr >= uint(bufIndex) {
+		return StructuralError("origPtr out of bounds")
+	}
+
+	// We have completed the entropy decoding. Now we can perform the
+	// inverse BWT and setup the RLE buffer.
+	bz2.preRLE = bz2.tt[:bufIndex]
+	bz2.preRLEUsed = 0
+	bz2.tPos = inverseBWT(bz2.preRLE, origPtr, bz2.c[:])
+	bz2.lastByte = -1
+	bz2.byteRepeats = 0
+	bz2.repeats = 0
+
+	return nil
+}
+
+// inverseBWT implements the inverse Burrows-Wheeler transform as described in
+// http://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-124.pdf, section 4.2.
+// In that document, origPtr is called `I' and c is the `C' array after the
+// first pass over the data. It's an argument here because we merge the first
+// pass with the Huffman decoding.
+//
+// This also implements the `single array' method from the bzip2 source code
+// which leaves the output, still shuffled, in the bottom 8 bits of tt with the
+// index of the next byte in the top 24-bits. The index of the first byte is
+// returned.
+func inverseBWT(tt []uint32, origPtr uint, c []uint) uint32 {
+	sum := uint(0)
+	for i := 0; i < 256; i++ {
+		sum += c[i]
+		c[i] = sum - c[i]
+	}
+
+	for i := range tt {
+		b := tt[i] & 0xff
+		tt[c[b]] |= uint32(i) << 8
+		c[b]++
+	}
+
+	return tt[origPtr] >> 8
+}
+
+// This is a standard CRC32 like in hash/crc32 except that all the shifts are reversed,
+// causing the bits in the input to be processed in the reverse of the usual order.
+
+var crctab [256]uint32
+
+func init() {
+	const poly = 0x04C11DB7
+	for i := range crctab {
+		crc := uint32(i) << 24
+		for j := 0; j < 8; j++ {
+			if crc&0x80000000 != 0 {
+				crc = (crc << 1) ^ poly
+			} else {
+				crc <<= 1
+			}
+		}
+		crctab[i] = crc
+	}
+}
+
+// updateCRC updates the crc value to incorporate the data in b.
+// The initial value is 0.
+func updateCRC(val uint32, b []byte) uint32 {
+	crc := ^val
+	for _, v := range b {
+		crc = crctab[byte(crc>>24)^v] ^ (crc << 8)
+	}
+	return ^crc
+}
diff --git a/src/compress/bzip2/bzip2_test.go b/src/compress/bzip2/bzip2_test.go
new file mode 100644
index 000000000..fb79d089e
--- /dev/null
+++ b/src/compress/bzip2/bzip2_test.go
@@ -0,0 +1,419 @@
+// 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 bzip2
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/hex"
+	"io"
+	"io/ioutil"
+	"testing"
+)
+
+func TestBitReader(t *testing.T) {
+	buf := bytes.NewReader([]byte{0xaa})
+	br := newBitReader(buf)
+	if n := br.ReadBits(1); n != 1 {
+		t.Errorf("read 1 wrong")
+	}
+	if n := br.ReadBits(1); n != 0 {
+		t.Errorf("read 2 wrong")
+	}
+	if n := br.ReadBits(1); n != 1 {
+		t.Errorf("read 3 wrong")
+	}
+	if n := br.ReadBits(1); n != 0 {
+		t.Errorf("read 4 wrong")
+	}
+}
+
+func TestBitReaderLarge(t *testing.T) {
+	buf := bytes.NewReader([]byte{0x12, 0x34, 0x56, 0x78})
+	br := newBitReader(buf)
+	if n := br.ReadBits(32); n != 0x12345678 {
+		t.Errorf("got: %x want: %x", n, 0x12345678)
+	}
+}
+
+func readerFromHex(s string) io.Reader {
+	data, err := hex.DecodeString(s)
+	if err != nil {
+		panic("readerFromHex: bad input")
+	}
+	return bytes.NewReader(data)
+}
+
+func decompressHex(s string) (out []byte, err error) {
+	r := NewReader(readerFromHex(s))
+	return ioutil.ReadAll(r)
+}
+
+func TestHelloWorldBZ2(t *testing.T) {
+	out, err := decompressHex(helloWorldBZ2Hex)
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+
+	if !bytes.Equal(helloWorld, out) {
+		t.Errorf("got %x, want %x", out, helloWorld)
+	}
+}
+
+func TestConcat(t *testing.T) {
+	out, err := decompressHex(helloWorldBZ2Hex + helloWorldBZ2Hex)
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+
+	hello2 := bytes.Repeat(helloWorld, 2)
+	if !bytes.Equal(hello2, out) {
+		t.Errorf("got %x, want %x", out, hello2)
+	}
+}
+
+func testZeros(t *testing.T, inHex string, n int) {
+	out, err := decompressHex(inHex)
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+
+	expected := make([]byte, n)
+
+	if !bytes.Equal(expected, out) {
+		allZeros := true
+		for _, b := range out {
+			if b != 0 {
+				allZeros = false
+				break
+			}
+		}
+		t.Errorf("incorrect result, got %d bytes (allZeros: %t)", len(out), allZeros)
+	}
+}
+
+func Test32Zeros(t *testing.T) {
+	testZeros(t, thirtyTwoZerosBZ2Hex, 32)
+}
+
+func Test1MBZeros(t *testing.T) {
+	testZeros(t, oneMBZerosBZ2Hex, 1024*1024)
+}
+
+func testRandomData(t *testing.T, compressedHex, uncompressedHex string) {
+	out, err := decompressHex(compressedHex)
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+
+	expected, _ := hex.DecodeString(uncompressedHex)
+
+	if !bytes.Equal(out, expected) {
+		t.Errorf("incorrect result\ngot:  %x\nwant: %x", out, expected)
+	}
+}
+
+func TestRandomData1(t *testing.T) {
+	testRandomData(t, randBZ2Hex, randHex)
+}
+
+func TestRandomData2(t *testing.T) {
+	// This test involves several repeated bytes in the output, but they
+	// should trigger RLE decoding.
+	testRandomData(t, rand2BZ2Hex, rand2Hex)
+}
+
+func TestRandomData3(t *testing.T) {
+	// This test uses the full range of symbols.
+	testRandomData(t, rand3BZ2Hex, rand3Hex)
+}
+
+func Test1MBSawtooth(t *testing.T) {
+	out, err := decompressHex(oneMBSawtoothBZ2Hex)
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+
+	expected := make([]byte, 1024*1024)
+
+	for i := range expected {
+		expected[i] = byte(i)
+	}
+
+	if !bytes.Equal(out, expected) {
+		t.Error("incorrect result")
+	}
+}
+
+const helloWorldBZ2Hex = "425a68393141592653594eece83600000251800010400006449080200031064c4101a7a9a580bb9431f8bb9229c28482776741b0"
+
+var helloWorld = []byte("hello world\n")
+
+const thirtyTwoZerosBZ2Hex = "425a6839314159265359b5aa5098000000600040000004200021008283177245385090b5aa5098"
+const oneMBZerosBZ2Hex = "425a683931415926535938571ce50008084000c0040008200030cc0529a60806c4201e2ee48a70a12070ae39ca"
+
+const randBZ2Hex = "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"
+const randHex = "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"
+
+const oneMBSawtoothBZ2Hex = "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"
+
+const rand2BZ2Hex = "425a6839314159265359d992d0f60000137dfe84020310091c1e280e100e042801099210094806c0110002e70806402000546034000034000000f2830000032000d3403264049270eb7a9280d308ca06ad28f6981bee1bf8160727c7364510d73a1e123083421b63f031f63993a0f40051fbf177245385090d992d0f60"
+const rand2Hex = "92d5652616ac444a4a04af1a8a3964aca0450d43d6cf233bd03233f4ba92f8719e6c2a2bd4f5f88db07ecd0da3a33b263483db9b2c158786ad6363be35d17335ba"
+
+const rand3BZ2Hex = "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"
+const rand3Hex = "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"
+
+const (
+	digits = iota
+	twain
+)
+
+var testfiles = []string{
+	// Digits is the digits of the irrational number e. Its decimal representation
+	// does not repeat, but there are only 10 possible digits, so it should be
+	// reasonably compressible.
+	digits: "testdata/e.txt.bz2",
+	// Twain is Project Gutenberg's edition of Mark Twain's classic English novel.
+	twain: "testdata/Mark.Twain-Tom.Sawyer.txt.bz2",
+}
+
+func benchmarkDecode(b *testing.B, testfile int) {
+	compressed, err := ioutil.ReadFile(testfiles[testfile])
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.SetBytes(int64(len(compressed)))
+	for i := 0; i < b.N; i++ {
+		r := bytes.NewReader(compressed)
+		io.Copy(ioutil.Discard, NewReader(r))
+	}
+}
+
+func BenchmarkDecodeDigits(b *testing.B) { benchmarkDecode(b, digits) }
+func BenchmarkDecodeTwain(b *testing.B)  { benchmarkDecode(b, twain) }
+
+func TestBufferOverrun(t *testing.T) {
+	// Tests https://code.google.com/p/go/issues/detail?id=5747.
+	buffer := bytes.NewReader([]byte(bufferOverrunBase64))
+	decoder := base64.NewDecoder(base64.StdEncoding, buffer)
+	decompressor := NewReader(decoder)
+	// This shouldn't panic.
+	ioutil.ReadAll(decompressor)
+}
+
+func TestOutOfRangeSelector(t *testing.T) {
+	// Tests https://code.google.com/p/go/issues/detail?id=8363.
+	buffer := bytes.NewReader(outOfRangeSelector)
+	decompressor := NewReader(buffer)
+	// This shouldn't panic.
+	ioutil.ReadAll(decompressor)
+}
+
+func TestMTF(t *testing.T) {
+	mtf := newMTFDecoderWithRange(5)
+
+	// 0 1 2 3 4
+	expect := byte(1)
+	x := mtf.Decode(1)
+	if x != expect {
+		t.Errorf("expected %v, got %v", expect, x)
+	}
+
+	// 1 0 2 3 4
+	x = mtf.Decode(0)
+	if x != expect {
+		t.Errorf("expected %v, got %v", expect, x)
+	}
+
+	// 1 0 2 3 4
+	expect = byte(0)
+	x = mtf.Decode(1)
+	if x != expect {
+		t.Errorf("expected %v, got %v", expect, x)
+	}
+
+	// 0 1 2 3 4
+	expect = byte(4)
+	x = mtf.Decode(4)
+	if x != expect {
+		t.Errorf("expected %v, got %v", expect, x)
+	}
+
+	// 4 0 1 2 3
+	expect = byte(0)
+	x = mtf.Decode(1)
+	if x != expect {
+		t.Errorf("expected %v, got %v", expect, x)
+	}
+}
+
+var bufferOverrunBase64 string = `
+QlpoNTFBWSZTWTzyiGcACMP/////////////////////////////////3/7f3///
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+4QmLmkHt7LxB2pAczUO+T2O9bHEw/HWw+dYf2MoRDUw=
+`
+
+var outOfRangeSelector = []byte{
+	0x42, 0x5a, 0x68, 0x39, 0x31, 0x41, 0x59, 0x26,
+	0x53, 0x59, 0x4e, 0xec, 0xe8, 0x36, 0x00, 0x00,
+	0x02, 0x51, 0x80, 0x00, 0x10, 0x40, 0x00, 0x06,
+	0x44, 0x90, 0x80, 0x20, 0x00, 0x31, 0x06, 0x4c,
+	0x41, 0x01, 0xa7, 0xa9, 0xa5, 0x80, 0xbb, 0x94,
+	0x31, 0x17, 0x72, 0x45, 0x38, 0x50, 0x90, 0x00,
+	0x00, 0x00, 0x00,
+}
diff --git a/src/compress/bzip2/huffman.go b/src/compress/bzip2/huffman.go
new file mode 100644
index 000000000..75a6223d8
--- /dev/null
+++ b/src/compress/bzip2/huffman.go
@@ -0,0 +1,251 @@
+// 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 bzip2
+
+import "sort"
+
+// A huffmanTree is a binary tree which is navigated, bit-by-bit to reach a
+// symbol.
+type huffmanTree struct {
+	// nodes contains all the non-leaf nodes in the tree. nodes[0] is the
+	// root of the tree and nextNode contains the index of the next element
+	// of nodes to use when the tree is being constructed.
+	nodes    []huffmanNode
+	nextNode int
+}
+
+// A huffmanNode is a node in the tree. left and right contain indexes into the
+// nodes slice of the tree. If left or right is invalidNodeValue then the child
+// is a left node and its value is in leftValue/rightValue.
+//
+// The symbols are uint16s because bzip2 encodes not only MTF indexes in the
+// tree, but also two magic values for run-length encoding and an EOF symbol.
+// Thus there are more than 256 possible symbols.
+type huffmanNode struct {
+	left, right           uint16
+	leftValue, rightValue uint16
+}
+
+// invalidNodeValue is an invalid index which marks a leaf node in the tree.
+const invalidNodeValue = 0xffff
+
+// Decode reads bits from the given bitReader and navigates the tree until a
+// symbol is found.
+func (t *huffmanTree) Decode(br *bitReader) (v uint16) {
+	nodeIndex := uint16(0) // node 0 is the root of the tree.
+
+	for {
+		node := &t.nodes[nodeIndex]
+		bit, ok := br.TryReadBit()
+		if !ok && br.ReadBit() {
+			bit = 1
+		}
+		// bzip2 encodes left as a true bit.
+		if bit != 0 {
+			// left
+			if node.left == invalidNodeValue {
+				return node.leftValue
+			}
+			nodeIndex = node.left
+		} else {
+			// right
+			if node.right == invalidNodeValue {
+				return node.rightValue
+			}
+			nodeIndex = node.right
+		}
+	}
+}
+
+// newHuffmanTree builds a Huffman tree from a slice containing the code
+// lengths of each symbol. The maximum code length is 32 bits.
+func newHuffmanTree(lengths []uint8) (huffmanTree, error) {
+	// There are many possible trees that assign the same code length to
+	// each symbol (consider reflecting a tree down the middle, for
+	// example). Since the code length assignments determine the
+	// efficiency of the tree, each of these trees is equally good. In
+	// order to minimize the amount of information needed to build a tree
+	// bzip2 uses a canonical tree so that it can be reconstructed given
+	// only the code length assignments.
+
+	if len(lengths) < 2 {
+		panic("newHuffmanTree: too few symbols")
+	}
+
+	var t huffmanTree
+
+	// First we sort the code length assignments by ascending code length,
+	// using the symbol value to break ties.
+	pairs := huffmanSymbolLengthPairs(make([]huffmanSymbolLengthPair, len(lengths)))
+	for i, length := range lengths {
+		pairs[i].value = uint16(i)
+		pairs[i].length = length
+	}
+
+	sort.Sort(pairs)
+
+	// Now we assign codes to the symbols, starting with the longest code.
+	// We keep the codes packed into a uint32, at the most-significant end.
+	// So branches are taken from the MSB downwards. This makes it easy to
+	// sort them later.
+	code := uint32(0)
+	length := uint8(32)
+
+	codes := huffmanCodes(make([]huffmanCode, len(lengths)))
+	for i := len(pairs) - 1; i >= 0; i-- {
+		if length > pairs[i].length {
+			// If the code length decreases we shift in order to
+			// zero any bits beyond the end of the code.
+			length >>= 32 - pairs[i].length
+			length <<= 32 - pairs[i].length
+			length = pairs[i].length
+		}
+		codes[i].code = code
+		codes[i].codeLen = length
+		codes[i].value = pairs[i].value
+		// We need to 'increment' the code, which means treating |code|
+		// like a |length| bit number.
+		code += 1 << (32 - length)
+	}
+
+	// Now we can sort by the code so that the left half of each branch are
+	// grouped together, recursively.
+	sort.Sort(codes)
+
+	t.nodes = make([]huffmanNode, len(codes))
+	_, err := buildHuffmanNode(&t, codes, 0)
+	return t, err
+}
+
+// huffmanSymbolLengthPair contains a symbol and its code length.
+type huffmanSymbolLengthPair struct {
+	value  uint16
+	length uint8
+}
+
+// huffmanSymbolLengthPair is used to provide an interface for sorting.
+type huffmanSymbolLengthPairs []huffmanSymbolLengthPair
+
+func (h huffmanSymbolLengthPairs) Len() int {
+	return len(h)
+}
+
+func (h huffmanSymbolLengthPairs) Less(i, j int) bool {
+	if h[i].length < h[j].length {
+		return true
+	}
+	if h[i].length > h[j].length {
+		return false
+	}
+	if h[i].value < h[j].value {
+		return true
+	}
+	return false
+}
+
+func (h huffmanSymbolLengthPairs) Swap(i, j int) {
+	h[i], h[j] = h[j], h[i]
+}
+
+// huffmanCode contains a symbol, its code and code length.
+type huffmanCode struct {
+	code    uint32
+	codeLen uint8
+	value   uint16
+}
+
+// huffmanCodes is used to provide an interface for sorting.
+type huffmanCodes []huffmanCode
+
+func (n huffmanCodes) Len() int {
+	return len(n)
+}
+
+func (n huffmanCodes) Less(i, j int) bool {
+	return n[i].code < n[j].code
+}
+
+func (n huffmanCodes) Swap(i, j int) {
+	n[i], n[j] = n[j], n[i]
+}
+
+// buildHuffmanNode takes a slice of sorted huffmanCodes and builds a node in
+// the Huffman tree at the given level. It returns the index of the newly
+// constructed node.
+func buildHuffmanNode(t *huffmanTree, codes []huffmanCode, level uint32) (nodeIndex uint16, err error) {
+	test := uint32(1) << (31 - level)
+
+	// We have to search the list of codes to find the divide between the left and right sides.
+	firstRightIndex := len(codes)
+	for i, code := range codes {
+		if code.code&test != 0 {
+			firstRightIndex = i
+			break
+		}
+	}
+
+	left := codes[:firstRightIndex]
+	right := codes[firstRightIndex:]
+
+	if len(left) == 0 || len(right) == 0 {
+		// There is a superfluous level in the Huffman tree indicating
+		// a bug in the encoder. However, this bug has been observed in
+		// the wild so we handle it.
+
+		// If this function was called recursively then we know that
+		// len(codes) >= 2 because, otherwise, we would have hit the
+		// "leaf node" case, below, and not recursed.
+		//
+		// However, for the initial call it's possible that len(codes)
+		// is zero or one. Both cases are invalid because a zero length
+		// tree cannot encode anything and a length-1 tree can only
+		// encode EOF and so is superfluous. We reject both.
+		if len(codes) < 2 {
+			return 0, StructuralError("empty Huffman tree")
+		}
+
+		// In this case the recursion doesn't always reduce the length
+		// of codes so we need to ensure termination via another
+		// mechanism.
+		if level == 31 {
+			// Since len(codes) >= 2 the only way that the values
+			// can match at all 32 bits is if they are equal, which
+			// is invalid. This ensures that we never enter
+			// infinite recursion.
+			return 0, StructuralError("equal symbols in Huffman tree")
+		}
+
+		if len(left) == 0 {
+			return buildHuffmanNode(t, right, level+1)
+		}
+		return buildHuffmanNode(t, left, level+1)
+	}
+
+	nodeIndex = uint16(t.nextNode)
+	node := &t.nodes[t.nextNode]
+	t.nextNode++
+
+	if len(left) == 1 {
+		// leaf node
+		node.left = invalidNodeValue
+		node.leftValue = left[0].value
+	} else {
+		node.left, err = buildHuffmanNode(t, left, level+1)
+	}
+
+	if err != nil {
+		return
+	}
+
+	if len(right) == 1 {
+		// leaf node
+		node.right = invalidNodeValue
+		node.rightValue = right[0].value
+	} else {
+		node.right, err = buildHuffmanNode(t, right, level+1)
+	}
+
+	return
+}
diff --git a/src/compress/bzip2/move_to_front.go b/src/compress/bzip2/move_to_front.go
new file mode 100644
index 000000000..526dfb34c
--- /dev/null
+++ b/src/compress/bzip2/move_to_front.go
@@ -0,0 +1,53 @@
+// 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 bzip2
+
+// moveToFrontDecoder implements a move-to-front list. Such a list is an
+// efficient way to transform a string with repeating elements into one with
+// many small valued numbers, which is suitable for entropy encoding. It works
+// by starting with an initial list of symbols and references symbols by their
+// index into that list. When a symbol is referenced, it's moved to the front
+// of the list. Thus, a repeated symbol ends up being encoded with many zeros,
+// as the symbol will be at the front of the list after the first access.
+type moveToFrontDecoder []byte
+
+// newMTFDecoder creates a move-to-front decoder with an explicit initial list
+// of symbols.
+func newMTFDecoder(symbols []byte) moveToFrontDecoder {
+	if len(symbols) > 256 {
+		panic("too many symbols")
+	}
+	return moveToFrontDecoder(symbols)
+}
+
+// newMTFDecoderWithRange creates a move-to-front decoder with an initial
+// symbol list of 0...n-1.
+func newMTFDecoderWithRange(n int) moveToFrontDecoder {
+	if n > 256 {
+		panic("newMTFDecoderWithRange: cannot have > 256 symbols")
+	}
+
+	m := make([]byte, n)
+	for i := 0; i < n; i++ {
+		m[i] = byte(i)
+	}
+	return moveToFrontDecoder(m)
+}
+
+func (m moveToFrontDecoder) Decode(n int) (b byte) {
+	// Implement move-to-front with a simple copy. This approach
+	// beats more sophisticated approaches in benchmarking, probably
+	// because it has high locality of reference inside of a
+	// single cache line (most move-to-front operations have n < 64).
+	b = m[n]
+	copy(m[1:], m[:n])
+	m[0] = b
+	return
+}
+
+// First returns the symbol at the front of the list.
+func (m moveToFrontDecoder) First() byte {
+	return m[0]
+}
diff --git a/src/compress/bzip2/testdata/Mark.Twain-Tom.Sawyer.txt.bz2 b/src/compress/bzip2/testdata/Mark.Twain-Tom.Sawyer.txt.bz2
new file mode 100644
index 000000000..0bd61a6d4
--- /dev/null
+++ b/src/compress/bzip2/testdata/Mark.Twain-Tom.Sawyer.txt.bz2
diff --git a/src/compress/bzip2/testdata/e.txt.bz2 b/src/compress/bzip2/testdata/e.txt.bz2
new file mode 100644
index 000000000..65bf3b4c3
--- /dev/null
+++ b/src/compress/bzip2/testdata/e.txt.bz2