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strconv: simplify code for binary exponent float format

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Use optimized formatBits function to format mantissa and exponent.
Add benchmark for binary exponent float format.

on darwin/386

benchmark                         old ns/op     new ns/op     delta
BenchmarkAppendFloatBinaryExp     520           122           -76.54%

on darwin/amd64

benchmark                         old ns/op     new ns/op     delta
BenchmarkAppendFloatBinaryExp     76.9          84.3          +9.62%

Change-Id: If543552f1960e1655bed3a4130914e5eaa3aac69
Reviewed-on: https://go-review.googlesource.com/5600
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Martin Möhrmann 2015-02-13 15:59:54 +01:00 committed by Robert Griesemer
parent 84f53339be
commit d5b5d6702a
2 changed files with 20 additions and 31 deletions
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50
src/strconv/ftoa.go
View File

@ -47,7 +47,7 @@ func FormatFloat(f float64, fmt byte, prec, bitSize int) string {
// AppendFloat appends the string form of the floating-point number f,
// as generated by FormatFloat, to dst and returns the extended buffer.
func AppendFloat(dst []byte, f float64, fmt byte, prec int, bitSize int) []byte {
func AppendFloat(dst []byte, f float64, fmt byte, prec, bitSize int) []byte {
return genericFtoa(dst, f, fmt, prec, bitSize)
}
@ -418,39 +418,27 @@ func fmtF(dst []byte, neg bool, d decimalSlice, prec int) []byte {
return dst
}
// %b: -ddddddddp+ddd
// %b: -ddddddddp±ddd
func fmtB(dst []byte, neg bool, mant uint64, exp int, flt *floatInfo) []byte {
var buf [50]byte
w := len(buf)
exp -= int(flt.mantbits)
esign := byte('+')
if exp < 0 {
esign = '-'
exp = -exp
}
n := 0
for exp > 0 || n < 1 {
n++
w--
buf[w] = byte(exp%10 + '0')
exp /= 10
}
w--
buf[w] = esign
w--
buf[w] = 'p'
n = 0
for mant > 0 || n < 1 {
n++
w--
buf[w] = byte(mant%10 + '0')
mant /= 10
}
// sign
if neg {
w--
buf[w] = '-'
dst = append(dst, '-')
}
return append(dst, buf[w:]...)
// mantissa
dst, _ = formatBits(dst, mant, 10, false, true)
// p
dst = append(dst, 'p')
// ±exponent
exp -= int(flt.mantbits)
if exp >= 0 {
dst = append(dst, '+')
}
dst, _ = formatBits(dst, uint64(exp), 10, exp < 0, true)
return dst
}
func min(a, b int) int {

1
src/strconv/ftoa_test.go
View File

@ -227,6 +227,7 @@ func BenchmarkAppendFloatNegExp(b *testing.B) { benchmarkAppendFloat(b, -5.11e-
func BenchmarkAppendFloatBig(b *testing.B) {
benchmarkAppendFloat(b, 123456789123456789123456789, 'g', -1, 64)
}
func BenchmarkAppendFloatBinaryExp(b *testing.B) { benchmarkAppendFloat(b, -1, 'b', -1, 64) }
func BenchmarkAppendFloat32Integer(b *testing.B) { benchmarkAppendFloat(b, 33909, 'g', -1, 32) }
func BenchmarkAppendFloat32ExactFraction(b *testing.B) { benchmarkAppendFloat(b, 3.375, 'g', -1, 32) }