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 computes Sqrt(p*p + q*q), taking care to avoid
  12 // unnecessary overflow and underflow.
  13 //
  14 // Special cases are:
  15 //      Hypot(p, q) = +Inf if p or q is infinite
  16 //      Hypot(p, q) = NaN if p or q is NaN
  17 func Hypot(p, q float64) float64 {
  18         // TODO(rsc): Remove manual inlining of IsNaN, IsInf
  19         // when compiler does it for us
  20         // special cases
  21         switch {
  22         case p < -MaxFloat64 || p > MaxFloat64 || q < -MaxFloat64 || q > MaxFloat64: // IsInf(p, 0) || IsInf(q, 0):
  23                 return Inf(1)
  24         case p != p || q != q: // IsNaN(p) || IsNaN(q):
  25                 return NaN()
  26         }
  27         if p < 0 {
  28                 p = -p
  29         }
  30         if q < 0 {
  31                 q = -q
  32         }
  33         if p < q {
  34                 p, q = q, p
  35         }
  36         if p == 0 {
  37                 return 0
  38         }
  39         q = q / p
  40         return p * Sqrt(1+q*q)
  41 }