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-rw-r--r--src/math/logb.go50
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diff --git a/src/math/logb.go b/src/math/logb.go
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+// 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 returns the binary exponent of x.
+//
+// Special cases are:
+// Logb(±Inf) = +Inf
+// Logb(0) = -Inf
+// Logb(NaN) = NaN
+func Logb(x float64) float64 {
+ // special cases
+ switch {
+ case x == 0:
+ return Inf(-1)
+ case IsInf(x, 0):
+ return Inf(1)
+ case IsNaN(x):
+ return x
+ }
+ return float64(ilogb(x))
+}
+
+// Ilogb 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 {
+ // special cases
+ switch {
+ case x == 0:
+ return MinInt32
+ case IsNaN(x):
+ return MaxInt32
+ case 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
+}