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 5 package 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 func Ldexp(frac float64, exp int) float64 15 16 func ldexp(frac float64, exp int) float64 { 17 // special cases 18 switch { 19 case frac == 0: 20 return frac // correctly return -0 21 case IsInf(frac, 0) || IsNaN(frac): 22 return frac 23 } 24 frac, e := normalize(frac) 25 exp += e 26 x := Float64bits(frac) 27 exp += int(x>>shift)&mask - bias 28 if exp < -1074 { 29 return Copysign(0, frac) // underflow 30 } 31 if exp > 1023 { // overflow 32 if frac < 0 { 33 return Inf(-1) 34 } 35 return Inf(1) 36 } 37 var m float64 = 1 38 if exp < -1022 { // denormal 39 exp += 52 40 m = 1.0 / (1 << 52) // 2**-52 41 } 42 x &^= mask << shift 43 x |= uint64(exp+bias) << shift 44 return m * Float64frombits(x) 45 } 46
