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, int) float64 17 18func Ldexp(frac float64, exp int) float64 { 19 r := libc_ldexp(frac, exp) 20 21 // Work around a bug in the implementation of ldexp on Solaris 22 // 9. If multiplying a negative number by 2 raised to a 23 // negative exponent underflows, we want to return negative 24 // zero, but the Solaris 9 implementation returns positive 25 // zero. This workaround can be removed when and if we no 26 // longer care about Solaris 9. 27 if r == 0 && frac < 0 && exp < 0 { 28 r = Copysign(0, frac) 29 } 30 return r 31} 32 33func ldexp(frac float64, exp int) float64 { 34 // special cases 35 switch { 36 case frac == 0: 37 return frac // correctly return -0 38 case IsInf(frac, 0) || IsNaN(frac): 39 return frac 40 } 41 frac, e := normalize(frac) 42 exp += e 43 x := Float64bits(frac) 44 exp += int(x>>shift)&mask - bias 45 if exp < -1074 { 46 return Copysign(0, frac) // underflow 47 } 48 if exp > 1023 { // overflow 49 if frac < 0 { 50 return Inf(-1) 51 } 52 return Inf(1) 53 } 54 var m float64 = 1 55 if exp < -1022 { // denormal 56 exp += 52 57 m = 1.0 / (1 << 52) // 2**-52 58 } 59 x &^= mask << shift 60 x |= uint64(exp+bias) << shift 61 return m * Float64frombits(x) 62} 63