cmd/compile/internal/gc: there are no -0 floating-point constants

Fixes #12577.

Change-Id: Id469cd92f5f9436b0ef948ee1a252ed1842bc7aa
Reviewed-on: https://go-review.googlesource.com/16133
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Robert Griesemer 2015-10-20 14:45:36 -07:00
parent ff85f86877
commit 76285213b8
2 changed files with 84 additions and 6 deletions

View file

@ -113,7 +113,7 @@ func mpgetflt(a *Mpflt) float64 {
Yyerror("mpgetflt ovf")
}
return x
return x + 0 // avoid -0 (should not be needed, but be conservative)
}
func mpgetflt32(a *Mpflt) float64 {
@ -125,7 +125,7 @@ func mpgetflt32(a *Mpflt) float64 {
Yyerror("mpgetflt32 ovf")
}
return x
return x + 0 // avoid -0 (should not be needed, but be conservative)
}
func Mpmovecflt(a *Mpflt, c float64) {
@ -133,6 +133,10 @@ func Mpmovecflt(a *Mpflt, c float64) {
fmt.Printf("\nconst %g", c)
}
// convert -0 to 0
if c == 0 {
c = 0
}
a.Val.SetFloat64(c)
if Mpdebug {
@ -141,7 +145,10 @@ func Mpmovecflt(a *Mpflt, c float64) {
}
func mpnegflt(a *Mpflt) {
a.Val.Neg(&a.Val)
// avoid -0
if a.Val.Sign() != 0 {
a.Val.Neg(&a.Val)
}
}
//
@ -163,15 +170,20 @@ func mpatoflt(a *Mpflt, as string) {
// - decimal point and binary point in constant
// TODO(gri) use different conversion function or check separately
Yyerror("malformed constant: %s", as)
a.Val.SetUint64(0)
a.Val.SetFloat64(0)
return
}
if f.IsInf() {
Yyerror("constant too large: %s", as)
a.Val.SetUint64(0)
a.Val.SetFloat64(0)
return
}
// -0 becomes 0
if f.Sign() == 0 && f.Signbit() {
a.Val.SetFloat64(0)
}
}
func (f *Mpflt) String() string {
@ -188,7 +200,7 @@ func Fconv(fvp *Mpflt, flag int) string {
// determine sign
f := &fvp.Val
var sign string
if fvp.Val.Signbit() {
if f.Sign() < 0 {
sign = "-"
f = new(big.Float).Abs(f)
} else if flag&obj.FmtSign != 0 {

View file

@ -0,0 +1,66 @@
// run
// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Issue 12577: Test that there are no -0 floating-point constants.
package main
import "math"
const (
z0 = 0.0
z1 = -0.0
z2 = -z0
z3 = -z2
)
var (
x0 float32 = z0
x1 float32 = z1
x2 float32 = z2
x3 float32 = z3
y0 float64 = z0
y1 float64 = z1
y2 float64 = z2
y3 float64 = z3
)
func test32(f float32) {
if f != 0 || math.Signbit(float64(f)) {
println("BUG: got", f, "want 0.0")
return
}
}
func test64(f float64) {
if f != 0 || math.Signbit(f) {
println("BUG: got", f, "want 0.0")
return
}
}
func main() {
if f := -x0; f != 0 || !math.Signbit(float64(f)) {
println("BUG: got", f, "want -0.0")
}
test32(-0.0)
test32(x0)
test32(x1)
test32(x2)
test32(x3)
if f := -y0; f != 0 || !math.Signbit(f) {
println("BUG: got", f, "want -0.0")
}
test64(-0.0)
test64(y0)
test64(y1)
test64(y2)
test64(y3)
}