libgo/go/math/mod.go

   1 // Copyright 2009-2010 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         Floating-point mod function.
   9 */
  10
  11 // Mod returns the floating-point remainder of x/y.
  12 // The magnitude of the result is less than y and its
  13 // sign agrees with that of x.
  14 //
  15 // Special cases are:
  16 //      Mod(±Inf, y) = NaN
  17 //      Mod(NaN, y) = NaN
  18 //      Mod(x, 0) = NaN
  19 //      Mod(x, ±Inf) = x
  20 //      Mod(x, NaN) = NaN
  21
  22 //extern fmod
  23 func libc_fmod(float64, float64) float64
  24
  25 func Mod(x, y float64) float64 {
  26         return libc_fmod(x, y)
  27 }
  28
  29 func mod(x, y float64) float64 {
  30         if y == 0 || IsInf(x, 0) || IsNaN(x) || IsNaN(y) {
  31                 return NaN()
  32         }
  33         if y < 0 {
  34                 y = -y
  35         }
  36
  37         yfr, yexp := Frexp(y)
  38         sign := false
  39         r := x
  40         if x < 0 {
  41                 r = -x
  42                 sign = true
  43         }
  44
  45         for r >= y {
  46                 rfr, rexp := Frexp(r)
  47                 if rfr < yfr {
  48                         rexp = rexp - 1
  49                 }
  50                 r = r - Ldexp(y, rexp-yexp)
  51         }
  52         if sign {
  53                 r = -r
  54         }
  55         return r
  56 }