libgo/go/math/hypot.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 math
   6
   7 /*
   8         Hypot -- sqrt(p*p + q*q), but overflows only if the result does.
   9 */
  10
  11 // Hypot returns Sqrt(p*p + q*q), taking care to avoid
  12 // unnecessary overflow and underflow.
  13 //
  14 // Special cases are:
  15 //      Hypot(±Inf, q) = +Inf
  16 //      Hypot(p, ±Inf) = +Inf
  17 //      Hypot(NaN, q) = NaN
  18 //      Hypot(p, NaN) = NaN
  19 func Hypot(p, q float64) float64 {
  20         return hypot(p, q)
  21 }
  22
  23 func hypot(p, q float64) float64 {
  24         // special cases
  25         switch {
  26         case IsInf(p, 0) || IsInf(q, 0):
  27                 return Inf(1)
  28         case IsNaN(p) || IsNaN(q):
  29                 return NaN()
  30         }
  31         if p < 0 {
  32                 p = -p
  33         }
  34         if q < 0 {
  35                 q = -q
  36         }
  37         if p < q {
  38                 p, q = q, p
  39         }
  40         if p == 0 {
  41                 return 0
  42         }
  43         q = q / p
  44         return p * Sqrt(1+q*q)
  45 }