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 } 63
