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math: Modf(-0) returns -0,-0 

Fixes #12867

Change-Id: I8ba81c622bce2a77a6142f941603198582eaf8a4
Reviewed-on: https://go-review.googlesource.com/15570
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Charlie Dorian 2015-10-07 18:23:28 -04:00 committed by Robert Griesemer
parent 821b54921a
commit 6fed2a68f7
3 changed files with 20 additions and 2 deletions
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4
src/math/all_test.go
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@ -447,7 +447,7 @@ var log2 = []float64{
var modf = [][2]float64{ var modf = [][2]float64{
{4.0000000000000000e+00, 9.7901192488367350108546816e-01}, {4.0000000000000000e+00, 9.7901192488367350108546816e-01},
{7.0000000000000000e+00, 7.3887247457810456552351752e-01}, {7.0000000000000000e+00, 7.3887247457810456552351752e-01},
{0.0000000000000000e+00, -2.7688005719200159404635997e-01}, {Copysign(0, -1), -2.7688005719200159404635997e-01},
{-5.0000000000000000e+00, -1.060361827107492160848778e-02}, {-5.0000000000000000e+00, -1.060361827107492160848778e-02},
{9.0000000000000000e+00, 6.3629370719841737980004837e-01}, {9.0000000000000000e+00, 6.3629370719841737980004837e-01},
{2.0000000000000000e+00, 9.2637723924396464525443662e-01}, {2.0000000000000000e+00, 9.2637723924396464525443662e-01},
@ -1356,11 +1356,13 @@ var log1pSC = []float64{
var vfmodfSC = []float64{ var vfmodfSC = []float64{
Inf(-1), Inf(-1),
Copysign(0, -1),
Inf(1), Inf(1),
NaN(), NaN(),
} }
var modfSC = [][2]float64{ var modfSC = [][2]float64{
{Inf(-1), NaN()}, // [2]float64{Copysign(0, -1), Inf(-1)}, {Inf(-1), NaN()}, // [2]float64{Copysign(0, -1), Inf(-1)},
{Copysign(0, -1), Copysign(0, -1)},
{Inf(1), NaN()}, // [2]float64{0, Inf(1)}, {Inf(1), NaN()}, // [2]float64{0, Inf(1)},
{NaN(), NaN()}, {NaN(), NaN()},
} }

5
src/math/modf.go
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@ -14,9 +14,12 @@ func Modf(f float64) (int float64, frac float64)
func modf(f float64) (int float64, frac float64) { func modf(f float64) (int float64, frac float64) {
if f < 1 { if f < 1 {
if f < 0 { switch {
case f < 0:
int, frac = Modf(-f) int, frac = Modf(-f)
return -int, -frac return -int, -frac
case f == 0:
return f, f // Return -0, -0 when f == -0
} }
return 0, f return 0, f
} }

13
src/math/modf_386.s
View File

@ -6,6 +6,19 @@
// func Modf(f float64) (int float64, frac float64) // func Modf(f float64) (int float64, frac float64)
TEXT ·Modf(SB),NOSPLIT,$0 TEXT ·Modf(SB),NOSPLIT,$0
// special case for f == -0.0
MOVL f+4(FP), DX // high word
MOVL f+0(FP), AX // low word
CMPL DX, $(1<<31) // beginning of -0.0
JNE notNegativeZero
CMPL AX, $0 // could be denormalized
JNE notNegativeZero
MOVL AX, int+8(FP)
MOVL DX, int+12(FP)
MOVL AX, frac+16(FP)
MOVL DX, frac+20(FP)
RET
notNegativeZero:
FMOVD f+0(FP), F0 // F0=f FMOVD f+0(FP), F0 // F0=f
FMOVD F0, F1 // F0=f, F1=f FMOVD F0, F1 // F0=f, F1=f
FSTCW -2(SP) // save old Control Word FSTCW -2(SP) // save old Control Word