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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

}