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// Copyright 2009 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

// Ldexp is the inverse of Frexp.

// It returns frac × 2**exp.

//

// Special cases are:

//      Ldexp(±0, exp) = ±0

//      Ldexp(±Inf, exp) = ±Inf

//      Ldexp(NaN, exp) = NaN

//extern ldexp

func libc_ldexp(float64, int) float64

func Ldexp(frac float64, exp int) float64 {

        return libc_ldexp(frac, exp)

}

func ldexp(frac float64, exp int) float64 {

        // special cases

        switch {

        case frac == 0:

                return frac // correctly return -0

        case IsInf(frac, 0) || IsNaN(frac):

                return frac

        }

        frac, e := normalize(frac)

        exp += e

        x := Float64bits(frac)

        exp += int(x>>shift)&mask - bias

        if exp < -1074 {

                return Copysign(0, frac) // underflow

        }

        if exp > 1023 { // overflow

                if frac < 0 {

                        return Inf(-1)

                }

                return Inf(1)

        }

        var m float64 = 1

        if exp < -1022 { // denormal

                exp += 52

                m = 1.0 / (1 << 52) // 2**-52

        }

        x &^= mask << shift

        x |= uint64(exp+bias) << shift

        return m * Float64frombits(x)

}