1 files changed, 131 insertions, 0 deletions
diff --git a/src/strconv/itoa.go b/src/strconv/itoa.go
new file mode 100644
index 000000000..67f17d866
--- /dev/null
+++ b/src/strconv/itoa.go
@@ -0,0 +1,131 @@
+// 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 strconv
+
+// FormatUint returns the string representation of i in the given base,
+// for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
+// for digit values >= 10.
+func FormatUint(i uint64, base int) string {
+	_, s := formatBits(nil, i, base, false, false)
+	return s
+}
+
+// FormatInt returns the string representation of i in the given base,
+// for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
+// for digit values >= 10.
+func FormatInt(i int64, base int) string {
+	_, s := formatBits(nil, uint64(i), base, i < 0, false)
+	return s
+}
+
+// Itoa is shorthand for FormatInt(i, 10).
+func Itoa(i int) string {
+	return FormatInt(int64(i), 10)
+}
+
+// AppendInt appends the string form of the integer i,
+// as generated by FormatInt, to dst and returns the extended buffer.
+func AppendInt(dst []byte, i int64, base int) []byte {
+	dst, _ = formatBits(dst, uint64(i), base, i < 0, true)
+	return dst
+}
+
+// AppendUint appends the string form of the unsigned integer i,
+// as generated by FormatUint, to dst and returns the extended buffer.
+func AppendUint(dst []byte, i uint64, base int) []byte {
+	dst, _ = formatBits(dst, i, base, false, true)
+	return dst
+}
+
+const (
+	digits   = "0123456789abcdefghijklmnopqrstuvwxyz"
+	digits01 = "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
+	digits10 = "0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999"
+)
+
+var shifts = [len(digits) + 1]uint{
+	1 << 1: 1,
+	1 << 2: 2,
+	1 << 3: 3,
+	1 << 4: 4,
+	1 << 5: 5,
+}
+
+// formatBits computes the string representation of u in the given base.
+// If neg is set, u is treated as negative int64 value. If append_ is
+// set, the string is appended to dst and the resulting byte slice is
+// returned as the first result value; otherwise the string is returned
+// as the second result value.
+//
+func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s string) {
+	if base < 2 || base > len(digits) {
+		panic("strconv: illegal AppendInt/FormatInt base")
+	}
+	// 2 <= base && base <= len(digits)
+
+	var a [64 + 1]byte // +1 for sign of 64bit value in base 2
+	i := len(a)
+
+	if neg {
+		u = -u
+	}
+
+	// convert bits
+	if base == 10 {
+		// common case: use constants for / and % because
+		// the compiler can optimize it into a multiply+shift,
+		// and unroll loop
+		for u >= 100 {
+			i -= 2
+			q := u / 100
+			j := uintptr(u - q*100)
+			a[i+1] = digits01[j]
+			a[i+0] = digits10[j]
+			u = q
+		}
+		if u >= 10 {
+			i--
+			q := u / 10
+			a[i] = digits[uintptr(u-q*10)]
+			u = q
+		}
+
+	} else if s := shifts[base]; s > 0 {
+		// base is power of 2: use shifts and masks instead of / and %
+		b := uint64(base)
+		m := uintptr(b) - 1 // == 1<<s - 1
+		for u >= b {
+			i--
+			a[i] = digits[uintptr(u)&m]
+			u >>= s
+		}
+
+	} else {
+		// general case
+		b := uint64(base)
+		for u >= b {
+			i--
+			a[i] = digits[uintptr(u%b)]
+			u /= b
+		}
+	}
+
+	// u < base
+	i--
+	a[i] = digits[uintptr(u)]
+
+	// add sign, if any
+	if neg {
+		i--
+		a[i] = '-'
+	}
+
+	if append_ {
+		d = append(dst, a[i:]...)
+		return
+	}
+	s = string(a[i:])
+	return
+}