github.com/primecitizens/pcz/std@v0.2.1/math/ldexp.go (about)

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