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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libgo/go/math/ldexp.go
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Diffstat (limited to 'libgo/go/math/ldexp.go')
-rw-r--r--libgo/go/math/ldexp.go45
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diff --git a/libgo/go/math/ldexp.go b/libgo/go/math/ldexp.go
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+// 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)
+}