1 files changed, 108 insertions, 38 deletions
diff --git a/src/pkg/strconv/itoa.go b/src/pkg/strconv/itoa.go
index a0a749664..ca40dd7ef 100644
--- a/src/pkg/strconv/itoa.go
+++ b/src/pkg/strconv/itoa.go
@@ -4,54 +4,124 @@
 
 package strconv
 
-// Uitob64 returns the string representation of i in the given base.
-func Uitob64(u uint64, base uint) string {
-	if base < 2 || 36 < base {
-		panic("invalid base " + Uitoa(base))
-	}
-	if u == 0 {
-		return "0"
-	}
+// FormatUint returns the string representation of i in the given base.
+func FormatUint(i uint64, base int) string {
+	_, s := formatBits(nil, i, base, false, false)
+	return s
+}
 
-	// Assemble decimal in reverse order.
-	var buf [64]byte
-	j := len(buf)
-	b := uint64(base)
-	for u > 0 {
-		j--
-		buf[j] = "0123456789abcdefghijklmnopqrstuvwxyz"[u%b]
-		u /= b
-	}
+// FormatInt returns the string representation of i in the given base.
+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
+}
 
-	return string(buf[j:])
+// 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
 }
 
-// Itob64 returns the string representation of i in the given base.
-func Itob64(i int64, base uint) string {
-	if i == 0 {
-		return "0"
+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)
 
-	if i < 0 {
-		return "-" + Uitob64(-uint64(i), base)
+	var a [64 + 1]byte // +1 for sign of 64bit value in base 2
+	i := len(a)
+
+	if neg {
+		u = -u
 	}
-	return Uitob64(uint64(i), base)
-}
 
-// Itoa64 returns the decimal string representation of i.
-func Itoa64(i int64) string { return Itob64(i, 10) }
+	// 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
+		}
 
-// Uitoa64 returns the decimal string representation of i.
-func Uitoa64(i uint64) string { return Uitob64(i, 10) }
+	} 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
+		}
 
-// Uitob returns the string representation of i in the given base.
-func Uitob(i uint, base uint) string { return Uitob64(uint64(i), base) }
+	} else {
+		// general case
+		b := uint64(base)
+		for u >= b {
+			i--
+			a[i] = digits[uintptr(u%b)]
+			u /= b
+		}
+	}
 
-// Itob returns the string representation of i in the given base.
-func Itob(i int, base uint) string { return Itob64(int64(i), base) }
+	// u < base
+	i--
+	a[i] = digits[uintptr(u)]
 
-// Itoa returns the decimal string representation of i.
-func Itoa(i int) string { return Itob64(int64(i), 10) }
+	// add sign, if any
+	if neg {
+		i--
+		a[i] = '-'
+	}
 
-// Uitoa returns the decimal string representation of i.
-func Uitoa(i uint) string { return Uitob64(uint64(i), 10) }
+	if append_ {
+		d = append(dst, a[i:]...)
+		return
+	}
+	s = string(a[i:])
+	return
+}