Imported Upstream version 2011-02-01.1upstream/2011-02-01.1

1 files changed, 20 insertions, 8 deletions

diff --git a/src/pkg/math/ldexp.go b/src/pkg/math/ldexp.go
index d04bf1581..96c95cad4 100644
--- a/src/pkg/math/ldexp.go
+++ b/src/pkg/math/ldexp.go
@@ -6,6 +6,11 @@ package math
 
 // Ldexp is the inverse of Frexp.
 // It returns frac × 2**exp.
+//
+// Special cases are:
+//	Ldexp(±0, exp) = ±0
+//	Ldexp(±Inf, exp) = ±Inf
+//	Ldexp(NaN, exp) = NaN
 func Ldexp(frac float64, exp int) float64 {
 	// TODO(rsc): Remove manual inlining of IsNaN, IsInf
 	// when compiler does it for us
@@ -13,21 +18,28 @@ func Ldexp(frac float64, exp int) float64 {
 	switch {
 	case frac == 0:
 		return frac // correctly return -0
-	case frac != frac: // IsNaN(frac):
-		return NaN()
+	case frac < -MaxFloat64 || frac > MaxFloat64 || frac != frac: // IsInf(frac, 0) || IsNaN(frac):
+		return frac
 	}
+	frac, e := normalize(frac)
+	exp += e
 	x := Float64bits(frac)
-	exp += int(x>>shift) & mask
-	if exp <= 0 {
-		return 0 // underflow
+	exp += int(x>>shift)&mask - bias
+	if exp < -1074 {
+		return Copysign(0, frac) // underflow
 	}
-	if exp >= mask { // overflow
+	if exp > 1023 { // overflow
 		if frac < 0 {
 			return Inf(-1)
 		}
 		return Inf(1)
 	}
+	var m float64 = 1
+	if exp < -1022 { // denormal
+		exp += 52
+		m = 1.0 / (1 << 52) // 2**-52
+	}
 	x &^= mask << shift
-	x |= uint64(exp) << shift
-	return Float64frombits(x)
+	x |= uint64(exp+bias) << shift
+	return m * Float64frombits(x)
 }