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>
diff --git a/src/cmd/compile/internal/gc/mparith3.go b/src/cmd/compile/internal/gc/mparith3.go
index f91a64b..4aa283f 100644
--- a/src/cmd/compile/internal/gc/mparith3.go
+++ b/src/cmd/compile/internal/gc/mparith3.go
@@ -113,7 +113,7 @@
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 @@
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 @@
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 mpnegflt(a *Mpflt) {
- a.Val.Neg(&a.Val)
+ // avoid -0
+ if a.Val.Sign() != 0 {
+ a.Val.Neg(&a.Val)
+ }
}
//
@@ -163,15 +170,20 @@
// - 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 @@
// 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 {
diff --git a/test/fixedbugs/issue12577.go b/test/fixedbugs/issue12577.go
new file mode 100644
index 0000000..249b4f2
--- /dev/null
+++ b/test/fixedbugs/issue12577.go
@@ -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)
+}
