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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/logb.go | |
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Diffstat (limited to 'libgo/go/math/logb.go')
-rw-r--r-- | libgo/go/math/logb.go | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/libgo/go/math/logb.go b/libgo/go/math/logb.go new file mode 100644 index 000000000..072281ddf --- /dev/null +++ b/libgo/go/math/logb.go @@ -0,0 +1,54 @@ +// Copyright 2010 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 + +// Logb(x) returns the binary exponent of x. +// +// Special cases are: +// Logb(±Inf) = +Inf +// Logb(0) = -Inf +// Logb(NaN) = NaN +func Logb(x float64) float64 { + // TODO(rsc): Remove manual inlining of IsNaN, IsInf + // when compiler does it for us + // special cases + switch { + case x == 0: + return Inf(-1) + case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0): + return Inf(1) + case x != x: // IsNaN(x): + return x + } + return float64(ilogb(x)) +} + +// Ilogb(x) returns the binary exponent of x as an integer. +// +// Special cases are: +// Ilogb(±Inf) = MaxInt32 +// Ilogb(0) = MinInt32 +// Ilogb(NaN) = MaxInt32 +func Ilogb(x float64) int { + // TODO(rsc): Remove manual inlining of IsNaN, IsInf + // when compiler does it for us + // special cases + switch { + case x == 0: + return MinInt32 + case x != x: // IsNaN(x): + return MaxInt32 + case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0): + return MaxInt32 + } + return ilogb(x) +} + +// logb returns the binary exponent of x. It assumes x is finite and +// non-zero. +func ilogb(x float64) int { + x, exp := normalize(x) + return int((Float64bits(x)>>shift)&mask) - bias + exp +} |