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// 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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