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8c6643846e
Removes init function from the math package. Allows stripping of arrays with pre-computed values used for Pow10 from binaries if Pow10 is not used. cmd/go shrinks by 128 bytes. Fixed small values like 10**-323 being 0 instead of 1e-323. Overall precision is increased but still not as good as predefined constants for some inputs. Samples: Pow10(208) before: 1.0000000000000006662e+208 after: 1.0000000000000000959e+208 Pow10(202) before 1.0000000000000009895e+202 after 1.0000000000000001193e+202 Pow10(60) before 1.0000000000000001278e+60 after 0.9999999999999999494e+60 Pow10(-100) before 0.99999999999999938551e-100 after 0.99999999999999989309e-100 Pow10(-200) before 0.9999999999999988218e-200 after 1.0000000000000001271e-200 name old time/op new time/op delta Pow10Pos-4 44.6ns ± 2% 1.2ns ± 1% -97.39% (p=0.000 n=19+17) Pow10Neg-4 50.8ns ± 1% 4.1ns ± 2% -92.02% (p=0.000 n=17+19) Change-Id: If094034286b8ac64be3a95fd9e8ffa3d4ad39b31 Reviewed-on: https://go-review.googlesource.com/36331 Reviewed-by: Robert Griesemer <gri@golang.org> Run-TryBot: Martin Möhrmann <moehrmann@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
47 lines
1.2 KiB
Go
47 lines
1.2 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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// pow10tab stores the pre-computed values 10**i for i < 32.
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var pow10tab = [...]float64{
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1e00, 1e01, 1e02, 1e03, 1e04, 1e05, 1e06, 1e07, 1e08, 1e09,
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1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
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1e20, 1e21, 1e22, 1e23, 1e24, 1e25, 1e26, 1e27, 1e28, 1e29,
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1e30, 1e31,
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}
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// pow10postab32 stores the pre-computed value for 10**(i*32) at index i.
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var pow10postab32 = [...]float64{
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1e00, 1e32, 1e64, 1e96, 1e128, 1e160, 1e192, 1e224, 1e256, 1e288,
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}
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// pow10negtab32 stores the pre-computed value for 10**(-i*32) at index i.
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var pow10negtab32 = [...]float64{
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1e-00, 1e-32, 1e-64, 1e-96, 1e-128, 1e-160, 1e-192, 1e-224, 1e-256, 1e-288, 1e-320,
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}
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// Pow10 returns 10**n, the base-10 exponential of n.
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//
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// Special cases are:
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// Pow10(n) = 0 for n < -323
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// Pow10(n) = +Inf for n > 308
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func Pow10(n int) float64 {
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if 0 <= n && n <= 308 {
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return pow10postab32[uint(n)/32] * pow10tab[uint(n)%32]
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}
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if -323 <= n && n <= 0 {
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return pow10negtab32[uint(-n)/32] / pow10tab[uint(-n)%32]
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}
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// n < -323 || 308 < n
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if n > 0 {
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return Inf(1)
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}
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// n < -323
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return 0
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}
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