Commit b219e8cb authored by Robert Griesemer's avatar Robert Griesemer

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
parent 02d1dae1
......@@ -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] = '-'
}
......
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