ldexp.go

Documentation: math

		 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  	if haveArchLdexp {
		16  		return archLdexp(frac, exp)
		17  	}
		18  	return ldexp(frac, exp)
		19  }
		20  
		21  func ldexp(frac float64, exp int) float64 {
		22  	// special cases
		23  	switch {
		24  	case frac == 0:
		25  		return frac // correctly return -0
		26  	case IsInf(frac, 0) || IsNaN(frac):
		27  		return frac
		28  	}
		29  	frac, e := normalize(frac)
		30  	exp += e
		31  	x := Float64bits(frac)
		32  	exp += int(x>>shift)&mask - bias
		33  	if exp < -1075 {
		34  		return Copysign(0, frac) // underflow
		35  	}
		36  	if exp > 1023 { // overflow
		37  		if frac < 0 {
		38  			return Inf(-1)
		39  		}
		40  		return Inf(1)
		41  	}
		42  	var m float64 = 1
		43  	if exp < -1022 { // denormal
		44  		exp += 53
		45  		m = 1.0 / (1 << 53) // 2**-53
		46  	}
		47  	x &^= mask << shift
		48  	x |= uint64(exp+bias) << shift
		49  	return m * Float64frombits(x)
		50  }
		51
View as plain text