complex.go

     1  // Copyright 2010 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 runtime
     6  
     7  // inf2one returns a signed 1 if f is an infinity and a signed 0 otherwise.
     8  // The sign of the result is the sign of f.
     9  func inf2one(f float64) float64 {
    10  	g := 0.0
    11  	if isInf(f) {
    12  		g = 1.0
    13  	}
    14  	return copysign(g, f)
    15  }
    16  
    17  func complex128div(n complex128, m complex128) complex128 {
    18  	var e, f float64 // complex(e, f) = n/m
    19  
    20  	// Algorithm for robust complex division as described in
    21  	// Robert L. Smith: Algorithm 116: Complex division. Commun. ACM 5(8): 435 (1962).
    22  	if abs(real(m)) >= abs(imag(m)) {
    23  		ratio := imag(m) / real(m)
    24  		denom := real(m) + ratio*imag(m)
    25  		e = (real(n) + imag(n)*ratio) / denom
    26  		f = (imag(n) - real(n)*ratio) / denom
    27  	} else {
    28  		ratio := real(m) / imag(m)
    29  		denom := imag(m) + ratio*real(m)
    30  		e = (real(n)*ratio + imag(n)) / denom
    31  		f = (imag(n)*ratio - real(n)) / denom
    32  	}
    33  
    34  	if isNaN(e) && isNaN(f) {
    35  		// Correct final result to infinities and zeros if applicable.
    36  		// Matches C99: ISO/IEC 9899:1999 - G.5.1  Multiplicative operators.
    37  
    38  		a, b := real(n), imag(n)
    39  		c, d := real(m), imag(m)
    40  
    41  		switch {
    42  		case m == 0 && (!isNaN(a) || !isNaN(b)):
    43  			e = copysign(inf, c) * a
    44  			f = copysign(inf, c) * b
    45  
    46  		case (isInf(a) || isInf(b)) && isFinite(c) && isFinite(d):
    47  			a = inf2one(a)
    48  			b = inf2one(b)
    49  			e = inf * (a*c + b*d)
    50  			f = inf * (b*c - a*d)
    51  
    52  		case (isInf(c) || isInf(d)) && isFinite(a) && isFinite(b):
    53  			c = inf2one(c)
    54  			d = inf2one(d)
    55  			e = 0 * (a*c + b*d)
    56  			f = 0 * (b*c - a*d)
    57  		}
    58  	}
    59  
    60  	return complex(e, f)
    61  }
    62
View as plain text