1// Copyright 2009 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5package math 6 7// Ldexp is the inverse of Frexp. 8// It returns frac × 2**exp. 9// 10// Special cases are: 11// Ldexp(±0, exp) = ±0 12// Ldexp(±Inf, exp) = ±Inf 13// Ldexp(NaN, exp) = NaN 14 15//extern ldexp 16func libc_ldexp(float64, int32) float64 17 18func Ldexp(frac float64, exp int) float64 { 19 if exp > MaxInt32 { 20 exp = MaxInt32 21 } else if exp < MinInt32 { 22 exp = MinInt32 23 } 24 r := libc_ldexp(frac, int32(exp)) 25 return r 26} 27 28func ldexp(frac float64, exp int) float64 { 29 // special cases 30 switch { 31 case frac == 0: 32 return frac // correctly return -0 33 case IsInf(frac, 0) || IsNaN(frac): 34 return frac 35 } 36 frac, e := normalize(frac) 37 exp += e 38 x := Float64bits(frac) 39 exp += int(x>>shift)&mask - bias 40 if exp < -1074 { 41 return Copysign(0, frac) // underflow 42 } 43 if exp > 1023 { // overflow 44 if frac < 0 { 45 return Inf(-1) 46 } 47 return Inf(1) 48 } 49 var m float64 = 1 50 if exp < -1022 { // denormal 51 exp += 52 52 m = 1.0 / (1 << 52) // 2**-52 53 } 54 x &^= mask << shift 55 x |= uint64(exp+bias) << shift 56 return m * Float64frombits(x) 57} 58