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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>
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@ -113,7 +113,7 @@ func mpgetflt(a *Mpflt) float64 {
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Yyerror("mpgetflt ovf")
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}
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return x
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return x + 0 // avoid -0 (should not be needed, but be conservative)
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}
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func mpgetflt32(a *Mpflt) float64 {
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@ -125,7 +125,7 @@ func mpgetflt32(a *Mpflt) float64 {
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Yyerror("mpgetflt32 ovf")
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}
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return x
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return x + 0 // avoid -0 (should not be needed, but be conservative)
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}
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func Mpmovecflt(a *Mpflt, c float64) {
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@ -133,6 +133,10 @@ func Mpmovecflt(a *Mpflt, c float64) {
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fmt.Printf("\nconst %g", c)
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}
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// convert -0 to 0
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if c == 0 {
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c = 0
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}
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a.Val.SetFloat64(c)
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if Mpdebug {
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@ -141,7 +145,10 @@ func Mpmovecflt(a *Mpflt, c float64) {
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}
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func mpnegflt(a *Mpflt) {
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a.Val.Neg(&a.Val)
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// avoid -0
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if a.Val.Sign() != 0 {
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a.Val.Neg(&a.Val)
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}
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}
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//
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@ -163,15 +170,20 @@ func mpatoflt(a *Mpflt, as string) {
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// - decimal point and binary point in constant
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// TODO(gri) use different conversion function or check separately
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Yyerror("malformed constant: %s", as)
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a.Val.SetUint64(0)
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a.Val.SetFloat64(0)
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return
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}
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if f.IsInf() {
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Yyerror("constant too large: %s", as)
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a.Val.SetUint64(0)
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a.Val.SetFloat64(0)
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return
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}
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// -0 becomes 0
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if f.Sign() == 0 && f.Signbit() {
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a.Val.SetFloat64(0)
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}
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}
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func (f *Mpflt) String() string {
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@ -188,7 +200,7 @@ func Fconv(fvp *Mpflt, flag int) string {
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// determine sign
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f := &fvp.Val
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var sign string
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if fvp.Val.Signbit() {
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if f.Sign() < 0 {
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sign = "-"
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f = new(big.Float).Abs(f)
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} else if flag&obj.FmtSign != 0 {
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66
test/fixedbugs/issue12577.go
Normal file
66
test/fixedbugs/issue12577.go
Normal file
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@ -0,0 +1,66 @@
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// run
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Issue 12577: Test that there are no -0 floating-point constants.
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package main
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import "math"
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const (
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z0 = 0.0
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z1 = -0.0
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z2 = -z0
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z3 = -z2
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)
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var (
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x0 float32 = z0
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x1 float32 = z1
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x2 float32 = z2
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x3 float32 = z3
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y0 float64 = z0
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y1 float64 = z1
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y2 float64 = z2
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y3 float64 = z3
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)
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func test32(f float32) {
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if f != 0 || math.Signbit(float64(f)) {
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println("BUG: got", f, "want 0.0")
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return
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}
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}
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func test64(f float64) {
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if f != 0 || math.Signbit(f) {
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println("BUG: got", f, "want 0.0")
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return
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}
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}
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func main() {
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if f := -x0; f != 0 || !math.Signbit(float64(f)) {
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println("BUG: got", f, "want -0.0")
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}
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test32(-0.0)
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test32(x0)
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test32(x1)
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test32(x2)
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test32(x3)
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if f := -y0; f != 0 || !math.Signbit(f) {
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println("BUG: got", f, "want -0.0")
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}
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test64(-0.0)
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test64(y0)
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test64(y1)
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test64(y2)
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test64(y3)
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}
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