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strconv: even faster int conversion

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benchmark                           old ns/op    new ns/op    delta
strconv_test.BenchmarkFormatInt         10038         8217  -18.14%
strconv_test.BenchmarkAppendInt          6822         4969  -27.16%
strconv_test.BenchmarkFormatUint         2811         1814  -35.47%
strconv_test.BenchmarkAppendUint         2349         1360  -42.10%

R=rsc
CC=golang-dev
https://golang.org/cl/5488083
This commit is contained in:
Robert Griesemer 2011-12-14 10:45:59 -08:00
parent 25e94154b7
commit 465aba66c1
1 changed files with 20 additions and 6 deletions
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26
src/pkg/strconv/itoa.go
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@ -35,7 +35,11 @@ func AppendUint(dst []byte, i uint64, base int) []byte {
return dst return dst
} }
const digits = "0123456789abcdefghijklmnopqrstuvwxyz" const (
digits = "0123456789abcdefghijklmnopqrstuvwxyz"
digits01 = "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
digits10 = "0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999"
)
var shifts = [len(digits) + 1]uint{ var shifts = [len(digits) + 1]uint{
1 << 1: 1, 1 << 1: 1,
@ -66,12 +70,22 @@ func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s
// convert bits // convert bits
if base == 10 { if base == 10 {
// common case: use constant 10 for / and % because // common case: use constants for / and % because
// the compiler can optimize it into a multiply+shift // the compiler can optimize it into a multiply+shift,
for u >= 10 { // and unroll loop
for u >= 100 {
i -= 2
q := u / 100
j := u - q*100
a[i+1] = digits01[j]
a[i+0] = digits10[j]
u = q
}
if u >= 10 {
i-- i--
a[i] = digits[u%10] q := u / 10
u /= 10 a[i] = digits[u-q*10]
u = q
} }
} else if s := shifts[base]; s > 0 { } else if s := shifts[base]; s > 0 {