libgo/go/math/nextafter.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 // Nextafter returns the next representable value after x towards y.
   8 // If x == y, then x is returned.
   9 //
  10 // Special cases are:
  11 //      Nextafter(NaN, y) = NaN
  12 //      Nextafter(x, NaN) = NaN
  13 func Nextafter(x, y float64) (r float64) {
  14         // TODO(rsc): Remove manual inlining of IsNaN
  15         // when compiler does it for us
  16         switch {
  17         case x != x || y != y: // IsNaN(x) || IsNaN(y): // special case
  18                 r = NaN()
  19         case x == y:
  20                 r = x
  21         case x == 0:
  22                 r = Copysign(Float64frombits(1), y)
  23         case (y > x) == (x > 0):
  24                 r = Float64frombits(Float64bits(x) + 1)
  25         default:
  26                 r = Float64frombits(Float64bits(x) - 1)
  27         }
  28         return r
  29 }