60 lines
1.8 KiB
Go
60 lines
1.8 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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const (
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uvnan = 0x7FF8000000000001
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uvinf = 0x7FF0000000000000
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uvneginf = 0xFFF0000000000000
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mask = 0x7FF
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shift = 64 - 11 - 1
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bias = 1023
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)
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// Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
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func Inf(sign int) float64 {
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var v uint64
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if sign >= 0 {
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v = uvinf
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} else {
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v = uvneginf
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}
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return Float64frombits(v)
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}
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// NaN returns an IEEE 754 ``not-a-number'' value.
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func NaN() float64 { return Float64frombits(uvnan) }
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// IsNaN returns whether f is an IEEE 754 ``not-a-number'' value.
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func IsNaN(f float64) (is bool) {
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// IEEE 754 says that only NaNs satisfy f != f.
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// To avoid the floating-point hardware, could use:
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// x := Float64bits(f);
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// return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
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return f != f
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}
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// IsInf returns whether f is an infinity, according to sign.
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// If sign > 0, IsInf returns whether f is positive infinity.
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// If sign < 0, IsInf returns whether f is negative infinity.
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// If sign == 0, IsInf returns whether f is either infinity.
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func IsInf(f float64, sign int) bool {
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// Test for infinity by comparing against maximum float.
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// To avoid the floating-point hardware, could use:
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// x := Float64bits(f);
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// return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
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return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
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}
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// normalize returns a normal number y and exponent exp
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// satisfying x == y × 2**exp. It assumes x is finite and non-zero.
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func normalize(x float64) (y float64, exp int) {
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const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
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if Abs(x) < SmallestNormal {
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return x * (1 << 52), -52
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}
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return x, 0
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}
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