| // Copyright 2009 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 math |
| |
| /* |
| * hypot -- sqrt(p*p + q*q), but overflows only if the result does. |
| * See Cleve Moler and Donald Morrison, |
| * Replacing Square Roots by Pythagorean Sums |
| * IBM Journal of Research and Development, |
| * Vol. 27, Number 6, pp. 577-581, Nov. 1983 |
| */ |
| |
| // Hypot computes Sqrt(p*p + q*q), taking care to avoid |
| // unnecessary overflow and underflow. |
| func Hypot(p, q float64) float64 { |
| if p < 0 { |
| p = -p; |
| } |
| if q < 0 { |
| q = -q; |
| } |
| |
| if p < q { |
| p, q = q, p; |
| } |
| |
| if p == 0 { |
| return 0; |
| } |
| |
| pfac := p; |
| q = q/p; |
| r := q; |
| p = 1; |
| for { |
| r = r*r; |
| s := r+4; |
| if s == 4 { |
| return p*pfac; |
| } |
| r = r/s; |
| p = p + 2*r*p; |
| q = q*r; |
| r = q/p; |
| } |
| panic("unreachable") |
| } |