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    = 0x7FF8000000000001
   9         uvinf    = 0x7FF0000000000000
  10         uvneginf = 0xFFF0000000000000
  11         uvone    = 0x3FF0000000000000
  12         mask     = 0x7FF
  13         shift    = 64 - 11 - 1
  14         bias     = 1023
  15         signMask = 1 << 63
  16         fracMask = 1<<shift - 1
  17 )
  18
  19 // Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
  20 func Inf(sign int) float64 {
  21         var v uint64
  22         if sign >= 0 {
  23                 v = uvinf
  24         } else {
  25                 v = uvneginf
  26         }
  27         return Float64frombits(v)
  28 }
  29
  30 // NaN returns an IEEE 754 ``not-a-number'' value.
  31 func NaN() float64 { return Float64frombits(uvnan) }
  32
  33 // IsNaN reports whether f is an IEEE 754 ``not-a-number'' value.
  34 func IsNaN(f float64) (is bool) {
  35         // IEEE 754 says that only NaNs satisfy f != f.
  36         // To avoid the floating-point hardware, could use:
  37         //      x := Float64bits(f);
  38         //      return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
  39         return f != f
  40 }
  41
  42 // IsInf reports whether f is an infinity, according to sign.
  43 // If sign > 0, IsInf reports whether f is positive infinity.
  44 // If sign < 0, IsInf reports whether f is negative infinity.
  45 // If sign == 0, IsInf reports whether f is either infinity.
  46 func IsInf(f float64, sign int) bool {
  47         // Test for infinity by comparing against maximum float.
  48         // To avoid the floating-point hardware, could use:
  49         //      x := Float64bits(f);
  50         //      return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
  51         return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
  52 }
  53
  54 // normalize returns a normal number y and exponent exp
  55 // satisfying x == y × 2**exp. It assumes x is finite and non-zero.
  56 func normalize(x float64) (y float64, exp int) {
  57         const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
  58         if Abs(x) < SmallestNormal {
  59                 return x * (1 << 52), -52
  60         }
  61         return x, 0
  62 }