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Source file src/runtime/complex.go

Documentation: runtime

  // Copyright 2010 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 runtime
  
  // inf2one returns a signed 1 if f is an infinity and a signed 0 otherwise.
  // The sign of the result is the sign of f.
  func inf2one(f float64) float64 {
  	g := 0.0
  	if isInf(f) {
  		g = 1.0
  	}
  	return copysign(g, f)
  }
  
  func complex128div(n complex128, m complex128) complex128 {
  	var e, f float64 // complex(e, f) = n/m
  
  	// Algorithm for robust complex division as described in
  	// Robert L. Smith: Algorithm 116: Complex division. Commun. ACM 5(8): 435 (1962).
  	if abs(real(m)) >= abs(imag(m)) {
  		ratio := imag(m) / real(m)
  		denom := real(m) + ratio*imag(m)
  		e = (real(n) + imag(n)*ratio) / denom
  		f = (imag(n) - real(n)*ratio) / denom
  	} else {
  		ratio := real(m) / imag(m)
  		denom := imag(m) + ratio*real(m)
  		e = (real(n)*ratio + imag(n)) / denom
  		f = (imag(n)*ratio - real(n)) / denom
  	}
  
  	if isNaN(e) && isNaN(f) {
  		// Correct final result to infinities and zeros if applicable.
  		// Matches C99: ISO/IEC 9899:1999 - G.5.1  Multiplicative operators.
  
  		a, b := real(n), imag(n)
  		c, d := real(m), imag(m)
  
  		switch {
  		case m == 0 && (!isNaN(a) || !isNaN(b)):
  			e = copysign(inf, c) * a
  			f = copysign(inf, c) * b
  
  		case (isInf(a) || isInf(b)) && isFinite(c) && isFinite(d):
  			a = inf2one(a)
  			b = inf2one(b)
  			e = inf * (a*c + b*d)
  			f = inf * (b*c - a*d)
  
  		case (isInf(c) || isInf(d)) && isFinite(a) && isFinite(b):
  			c = inf2one(c)
  			d = inf2one(d)
  			e = 0 * (a*c + b*d)
  			f = 0 * (b*c - a*d)
  		}
  	}
  
  	return complex(e, f)
  }
  

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