Source file src/runtime/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