64 lines
1.2 KiB
Go
64 lines
1.2 KiB
Go
// Copyright 2009-2010 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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/*
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Hypot -- sqrt(p*p + q*q), but overflows only if the result does.
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See:
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Cleve Moler and Donald Morrison,
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Replacing Square Roots by Pythagorean Sums
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IBM Journal of Research and Development,
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Vol. 27, Number 6, pp. 577-581, Nov. 1983
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*/
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// Hypot computes Sqrt(p*p + q*q), taking care to avoid
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// unnecessary overflow and underflow.
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//
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// Special cases are:
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// Hypot(p, q) = +Inf if p or q is infinite
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// Hypot(p, q) = NaN if p or q is NaN
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func hypotGo(p, q float64) float64 {
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// TODO(rsc): Remove manual inlining of IsNaN, IsInf
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// when compiler does it for us
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// special cases
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switch {
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case p < -MaxFloat64 || p > MaxFloat64 || q < -MaxFloat64 || q > MaxFloat64: // IsInf(p, 0) || IsInf(q, 0):
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return Inf(1)
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case p != p || q != q: // IsNaN(p) || IsNaN(q):
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return NaN()
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}
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if p < 0 {
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p = -p
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}
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if q < 0 {
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q = -q
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}
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if p < q {
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p, q = q, p
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}
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if p == 0 {
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return 0
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}
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pfac := p
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q = q / p
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r := q
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p = 1
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for {
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r = r * r
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s := r + 4
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if s == 4 {
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return p * pfac
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}
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r = r / s
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p = p + 2*r*p
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q = q * r
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r = q / p
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}
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panic("unreachable")
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}
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