51 lines
1.0 KiB
C
51 lines
1.0 KiB
C
/*
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* This file is part of the UCB release of Plan 9. It is subject to the license
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* terms in the LICENSE file found in the top-level directory of this
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* distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
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* part of the UCB release of Plan 9, including this file, may be copied,
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* modified, propagated, or distributed except according to the terms contained
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* in the LICENSE file.
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*/
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/*
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* hypot -- jehanne_sqrt(p*p+q*q), but overflows only if the result does.
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* See 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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#include <u.h>
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#include <libc.h>
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double
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jehanne_hypot(double p, double q)
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{
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double r, s, pfac;
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if(p < 0)
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p = -p;
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if(q < 0)
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q = -q;
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if(p < q) {
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r = p;
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p = q;
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q = r;
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}
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if(p == 0)
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return 0;
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pfac = p;
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r = q = q/p;
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p = 1;
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for(;;) {
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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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r /= s;
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p += 2*r*p;
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q *= r;
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r = q/p;
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}
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}
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