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Source file src/math/ldexp.go

Documentation: math

  // 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
  func Ldexp(frac float64, exp int) float64
  
  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)
  }
  

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