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fmt: remove math package dependency and avoid float operations

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Remove floating point comparisons and rely only on the information
directly provided by appendFloat.
Make restoring the zero padding flag explicit instead of using a defer.
Rearrange some case distinctions to remove duplicated code.
Add more test cases for zero padded floating point numbers with sign.

benchmark                   old ns/op     new ns/op     delta
BenchmarkSprintfFloat-4     187           180           -3.74%

Change-Id: Ifa2ae85257909f40b1b18118c92b516933271729
Reviewed-on: https://go-review.googlesource.com/19721
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Martin Möhrmann 2016-02-19 22:45:38 +01:00 committed by Rob Pike
parent 113c4d2581
commit 5a9c128a03
2 changed files with 23 additions and 26 deletions
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6
src/fmt/fmt_test.go
View File

@ -259,6 +259,12 @@ var fmtTests = []struct {
{"%+.3F", float32(-1.0), "-1.000"},
{"%+07.2f", 1.0, "+001.00"},
{"%+07.2f", -1.0, "-001.00"},
{"%-07.2f", 1.0, "1.00 "},
{"%-07.2f", -1.0, "-1.00 "},
{"%+-07.2f", 1.0, "+1.00 "},
{"%+-07.2f", -1.0, "-1.00 "},
{"%-+07.2f", 1.0, "+1.00 "},
{"%-+07.2f", -1.0, "-1.00 "},
{"%+10.2f", +1.0, " +1.00"},
{"%+10.2f", -1.0, " -1.00"},
{"% .3E", -1.0, "-1.000E+00"},

43
src/fmt/format.go
View File

@ -5,7 +5,6 @@
package fmt
import (
"math"
"strconv"
"unicode/utf8"
)
@ -405,42 +404,34 @@ func doPrec(f *fmt, def int) int {
// formatFloat formats a float64; it is an efficient equivalent to f.pad(strconv.FormatFloat()...).
func (f *fmt) formatFloat(v float64, verb byte, prec, n int) {
// Format number, reserving space for leading + sign if needed.
num := strconv.AppendFloat(f.intbuf[0:1], v, verb, prec, n)
num := strconv.AppendFloat(f.intbuf[:1], v, verb, prec, n)
if num[1] == '-' || num[1] == '+' {
num = num[1:]
} else {
num[0] = '+'
}
// Special handling for infinity, which doesn't look like a number so shouldn't be padded with zeros.
if math.IsInf(v, 0) {
if f.zero {
defer func() { f.zero = true }()
f.zero = false
}
}
// num is now a signed version of the number.
// If we're zero padding, want the sign before the leading zeros.
// Achieve this by writing the sign out and then padding the unsigned number.
if f.zero && f.widPresent && f.wid > len(num) {
if f.space && v >= 0 {
f.buf.WriteByte(' ') // This is what C does: even with zero, f.space means space.
f.wid--
} else if f.plus || v < 0 {
f.buf.WriteByte(num[0])
f.wid--
}
f.pad(num[1:])
return
}
// f.space says to replace a leading + with a space.
if f.space && num[0] == '+' {
num[0] = ' '
}
// Special handling for "+Inf" and "-Inf",
// which don't look like a number so shouldn't be padded with zeros.
if num[1] == 'I' {
oldZero := f.zero
f.zero = false
f.pad(num)
f.zero = oldZero
return
}
// Now we know the sign is attached directly to the number, if present at all.
// We want a sign if asked for, if it's negative, or if it's infinity (+Inf vs. -Inf).
if f.plus || num[0] == '-' || math.IsInf(v, 0) {
// We want a sign if asked for and if the sign is not positive.
if f.plus || num[0] != '+' {
// If we're zero padding we want the sign before the leading zeros.
// Achieve this by writing the sign out and then padding the unsigned number.
if f.zero && f.widPresent && f.wid > len(num) {
f.buf.WriteByte(num[0])
f.wid--
num = num[1:]
}
f.pad(num)
return
}