libgo/go/math/fmod.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 /*
   9         Floating-point mod function.
  10 */
  11
  12 // Fmod returns the floating-point remainder of x/y.
  13 // The magnitude of the result is less than y and its
  14 // sign agrees with that of x.
  15 //
  16 // Special cases are:
  17 //      if x is not finite, Fmod returns NaN
  18 //      if y is 0 or NaN, Fmod returns NaN
  19 func Fmod(x, y float64) float64 {
  20         // TODO(rsc): Remove manual inlining of IsNaN, IsInf
  21         // when compiler does it for us.
  22         if y == 0 || x > MaxFloat64 || x < -MaxFloat64 || x != x || y != y { // y == 0 || IsInf(x, 0) || IsNaN(x) || IsNan(y)
  23                 return NaN()
  24         }
  25         if y < 0 {
  26                 y = -y
  27         }
  28
  29         yfr, yexp := Frexp(y)
  30         sign := false
  31         r := x
  32         if x < 0 {
  33                 r = -x
  34                 sign = true
  35         }
  36
  37         for r >= y {
  38                 rfr, rexp := Frexp(r)
  39                 if rfr < yfr {
  40                         rexp = rexp - 1
  41                 }
  42                 r = r - Ldexp(y, rexp-yexp)
  43         }
  44         if sign {
  45                 r = -r
  46         }
  47         return r
  48 }