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
