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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(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
}
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