complex.go

Documentation: runtime

		 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
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