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math: faster hypot

Use hardware sqrt for faster hypot; preserve software-only
hypot as hypotGo (like sqrtGo); enable benchmarking of
hypotGo.

R=rsc
CC=golang-dev
https://golang.org/cl/229049
This commit is contained in:
Charles L. Dorian 2010-03-05 16:45:39 -08:00 committed by Russ Cox
parent ac499ed7a5
commit 067fe2840b
5 changed files with 81 additions and 24 deletions

View File

@ -54,6 +54,7 @@ ALLGOFILES=\
fmod.go\
frexp.go\
hypot.go\
hypot_port.go\
logb.go\
lgamma.go\
ldexp.go\

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@ -1754,6 +1754,12 @@ func BenchmarkHypot(b *testing.B) {
}
}
func BenchmarkHypotGo(b *testing.B) {
for i := 0; i < b.N; i++ {
HypotGo(3, 4)
}
}
func BenchmarkIlogb(b *testing.B) {
for i := 0; i < b.N; i++ {
Ilogb(.5)

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@ -1,4 +1,4 @@
// Copyright 2009-2010 The Go Authors. All rights reserved.
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
@ -6,11 +6,6 @@ package math
/*
Hypot -- sqrt(p*p + q*q), but overflows only if the result does.
See:
Cleve Moler and Donald Morrison,
Replacing Square Roots by Pythagorean Sums
IBM Journal of Research and Development,
Vol. 27, Number 6, pp. 577-581, Nov. 1983
*/
// Hypot computes Sqrt(p*p + q*q), taking care to avoid
@ -35,29 +30,12 @@ func Hypot(p, q float64) float64 {
if q < 0 {
q = -q
}
if p < q {
p, q = q, p
}
if p == 0 {
return 0
}
pfac := p
q = q / p
r := q
p = 1
for {
r = r * r
s := r + 4
if s == 4 {
return p * pfac
}
r = r / s
p = p + 2*r*p
q = q * r
r = q / p
}
panic("unreachable")
return p * Sqrt(1+q*q)
}

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@ -0,0 +1,63 @@
// Copyright 2009-2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
/*
Hypot -- sqrt(p*p + q*q), but overflows only if the result does.
See:
Cleve Moler and Donald Morrison,
Replacing Square Roots by Pythagorean Sums
IBM Journal of Research and Development,
Vol. 27, Number 6, pp. 577-581, Nov. 1983
*/
// Hypot computes Sqrt(p*p + q*q), taking care to avoid
// unnecessary overflow and underflow.
//
// Special cases are:
// Hypot(p, q) = +Inf if p or q is infinite
// Hypot(p, q) = NaN if p or q is NaN
func hypotGo(p, q float64) float64 {
// TODO(rsc): Remove manual inlining of IsNaN, IsInf
// when compiler does it for us
// special cases
switch {
case p < -MaxFloat64 || p > MaxFloat64 || q < -MaxFloat64 || q > MaxFloat64: // IsInf(p, 0) || IsInf(q, 0):
return Inf(1)
case p != p || q != q: // IsNaN(p) || IsNaN(q):
return NaN()
}
if p < 0 {
p = -p
}
if q < 0 {
q = -q
}
if p < q {
p, q = q, p
}
if p == 0 {
return 0
}
pfac := p
q = q / p
r := q
p = 1
for {
r = r * r
s := r + 4
if s == 4 {
return p * pfac
}
r = r / s
p = p + 2*r*p
q = q * r
r = q / p
}
panic("unreachable")
}

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@ -0,0 +1,9 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
// Make hypotGo available for testing.
func HypotGo(x, y float64) float64 { return hypotGo(x, y) }