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author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
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committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libgo/go/math/ldexp.go | |
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Diffstat (limited to 'libgo/go/math/ldexp.go')
-rw-r--r-- | libgo/go/math/ldexp.go | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/libgo/go/math/ldexp.go b/libgo/go/math/ldexp.go new file mode 100644 index 000000000..96c95cad4 --- /dev/null +++ b/libgo/go/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) +} |