Imported Upstream version 60upstream/60

1 files changed, 45 insertions, 0 deletions

diff --git a/src/pkg/math/ldexp.go b/src/pkg/math/ldexp.go
new file mode 100644
index 000000000..96c95cad4
--- /dev/null
+++ b/src/pkg/math/ldexp.go
@@ -0,0 +1,45 @@
+// Copyright 2009 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.
+
+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
+	// special cases
+	switch {
+	case frac == 0:
+		return frac // correctly return -0
+	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 - bias
+	if exp < -1074 {
+		return Copysign(0, frac) // underflow
+	}
+	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+bias) << shift
+	return m * Float64frombits(x)
+}