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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 {
        // 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(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 {
        // 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
}