49 lines
1.0 KiB
C
49 lines
1.0 KiB
C
/* ~(#)hypot.c 2.1 */
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/* ~(#)hypot.c 1.10 */
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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 ((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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