libgo/go/math/bits.go

   1 // Copyright 2009 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 const (
   8         uvnan    = 0x7FF0000000000001
   9         uvinf    = 0x7FF0000000000000
  10         uvneginf = 0xFFF0000000000000
  11         mask     = 0x7FF
  12         shift    = 64 - 11 - 1
  13         bias     = 1023
  14 )
  15
  16 // Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
  17 func Inf(sign int) float64 {
  18         var v uint64
  19         if sign >= 0 {
  20                 v = uvinf
  21         } else {
  22                 v = uvneginf
  23         }
  24         return Float64frombits(v)
  25 }
  26
  27 // NaN returns an IEEE 754 ``not-a-number'' value.
  28 func NaN() float64 { return Float64frombits(uvnan) }
  29
  30 // IsNaN returns whether f is an IEEE 754 ``not-a-number'' value.
  31 func IsNaN(f float64) (is bool) {
  32         // IEEE 754 says that only NaNs satisfy f != f.
  33         // To avoid the floating-point hardware, could use:
  34         //      x := Float64bits(f);
  35         //      return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
  36         return f != f
  37 }
  38
  39 // IsInf returns whether f is an infinity, according to sign.
  40 // If sign > 0, IsInf returns whether f is positive infinity.
  41 // If sign < 0, IsInf returns whether f is negative infinity.
  42 // If sign == 0, IsInf returns whether f is either infinity.
  43 func IsInf(f float64, sign int) bool {
  44         // Test for infinity by comparing against maximum float.
  45         // To avoid the floating-point hardware, could use:
  46         //      x := Float64bits(f);
  47         //      return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
  48         return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
  49 }
  50
  51 // normalize returns a normal number y and exponent exp
  52 // satisfying x == y × 2**exp. It assumes x is finite and non-zero.
  53 func normalize(x float64) (y float64, exp int) {
  54         const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
  55         if Abs(x) < SmallestNormal {
  56                 return x * (1 << 52), -52
  57         }
  58         return x, 0
  59 }