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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)
}