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-rw-r--r--src/runtime/complex.go61
1 files changed, 61 insertions, 0 deletions
diff --git a/src/runtime/complex.go b/src/runtime/complex.go
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+// 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)
+}