strconv: squeezed a bit more out of int/uint formatting

- less code
- slightly better performance (0-4%)

R=r, rsc
CC=golang-dev
https://golang.org/cl/5448120

diff --git a/src/pkg/strconv/itoa.go b/src/pkg/strconv/itoa.go
index 794ef370b26a7c52bc7bfde95cf2c992aaa05264..65229f704b8f4e6fcde0a65155e6ecd6f3ade34d 100644 (file)
--- a/src/pkg/strconv/itoa.go
+++ b/src/pkg/strconv/itoa.go
@@ -12,7 +12,7 @@ func FormatUint(i uint64, base int) string {
 
 // FormatInt returns the string representation of i in the given base.
 func FormatInt(i int64, base int) string {
-       _, s := formatBits(nil, uint64(i), base, true, false)
+       _, s := formatBits(nil, uint64(i), base, i < 0, false)
        return s
 }
 
@@ -24,7 +24,7 @@ func Itoa(i int) string {
 // 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, true, true)
+       dst, _ = formatBits(dst, uint64(i), base, i < 0, true)
        return dst
 }
 
@@ -46,31 +46,21 @@ var shifts = [len(digits) + 1]uint{
 }
 
 // formatBits computes the string representation of u in the given base.
-// If signed is set, u is treated as 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 simply returned as the
-// second result value.
+// If negative 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, signed, append_ bool) (d []byte, s string) {
+func formatBits(dst []byte, u uint64, base int, negative, append_ bool) (d []byte, s string) {
        if base < 2 || base > len(digits) {
                panic("invalid base")
        }
        // 2 <= base && base <= len(digits)
 
-       if u == 0 {
-               if append_ {
-                       d = append(dst, '0')
-                       return
-               }
-               s = "0"
-               return
-       }
-
        var a [64 + 1]byte // +1 for sign of 64bit value in base 2
        i := len(a)
 
-       x := int64(u)
-       if x < 0 && signed {
+       if negative {
                u = -u
        }
 
@@ -78,7 +68,7 @@ func formatBits(dst []byte, u uint64, base int, signed, append_ bool) (d []byte,
        if base == 10 {
                // common case: use constant 10 for / and % because
                // the compiler can optimize it into a multiply+shift
-               for u != 0 {
+               for u >= 10 {
                        i--
                        a[i] = digits[u%10]
                        u /= 10
@@ -86,8 +76,9 @@ func formatBits(dst []byte, u uint64, base int, signed, append_ bool) (d []byte,
 
        } else if s := shifts[base]; s > 0 {
                // base is power of 2: use shifts and masks instead of / and %
-               m := uintptr(1)<<s - 1
-               for u != 0 {
+               b := uint64(base)
+               m := uintptr(b) - 1 // == 1<<s - 1
+               for u >= b {
                        i--
                        a[i] = digits[uintptr(u)&m]
                        u >>= s
@@ -96,15 +87,19 @@ func formatBits(dst []byte, u uint64, base int, signed, append_ bool) (d []byte,
        } else {
                // general case
                b := uint64(base)
-               for u != 0 {
+               for u >= b {
                        i--
                        a[i] = digits[u%b]
                        u /= b
                }
        }
 
+       // u < base
+       i--
+       a[i] = digits[uintptr(u)]
+
        // add sign, if any
-       if x < 0 && signed {
+       if negative {
                i--
                a[i] = '-'
        }