59 lines
1.4 KiB
C
59 lines
1.4 KiB
C
#if !defined(lint) && defined(SCCSIDS)
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static char sccsid[] = "@(#)hypot.c 1.1 94/10/31 SMI"; /* from S5R3 1.13 */
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#endif
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/* Copyright (c) 1984 AT&T */
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/* All Rights Reserved */
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/* THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF AT&T */
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/* The copyright notice above does not evidence any */
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/* actual or intended publication of such source code. */
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/*LINTLIBRARY*/
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/*
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* hypot(a, b) returns sqrt(a^2 + b^2), avoiding unnecessary overflows.
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* Returns ERANGE error and value HUGE if the correct value would overflow.
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*/
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#include <math.h>
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#include <values.h>
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#include <errno.h>
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#define ITERATIONS 4
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double
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hypot(a, b)
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register double a, b;
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{
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register double t;
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register int i = ITERATIONS;
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struct exception exc;
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if ((exc.arg1 = a) < 0)
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a = -a;
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if ((exc.arg2 = b) < 0)
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b = -b;
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if (a > b) { /* make sure |a| <= |b| */
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t = a;
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a = b;
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b = t;
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}
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if(b == 0.0) return(b); /* both args are 0, result=0 */
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if ((t = a/b) < X_EPS) /* t <= 1 */
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return (b); /* t << 1 */
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a = 1 + t * t; /* a = 1 + (a/b)^2 */
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t = 0.5 + 0.5 * a; /* first guess for sqrt */
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do {
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t = 0.5 * (t + a/t);
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} while (--i > 0); /* t <= sqrt(2) */
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if (b < MAXDOUBLE/M_SQRT2) /* result can't overflow */
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return (t * b);
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if ((t *= 0.5 * b) < MAXDOUBLE/2) /* result won't overflow */
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return (t + t);
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exc.type = OVERFLOW;
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exc.name = "hypot";
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exc.retval = HUGE;
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if (!matherr(&exc))
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errno = ERANGE;
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return (exc.retval);
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}
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