55 lines
1 KiB
C
55 lines
1 KiB
C
/*
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* (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
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* See the copyright notice in the ACK home directory, in the file "Copyright".
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*
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* Author: Ceriel J.H. Jacobs
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*/
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/* $Id$ */
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#include <math.h>
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#include <float.h>
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#include <errno.h>
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#include "localmath.h"
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double
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pow(double x, double y)
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{
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/* Simple version for now. The Cody and Waite book has
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a very complicated, much more precise version, but
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this version has machine-dependent arrays A1 and A2,
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and I don't know yet how to solve this ???
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*/
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double dummy;
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int result_neg = 0;
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if ((x == 0 && y == 0) ||
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(x < 0 && modf(y, &dummy) != 0)) {
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errno = EDOM;
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return 0;
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}
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if (x == 0) return x;
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if (x < 0) {
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if (modf(y/2.0, &dummy) != 0) {
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/* y was odd */
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result_neg = 1;
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}
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x = -x;
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}
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x = log(x);
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if (x < 0) {
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x = -x;
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y = -y;
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}
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/* Beware of overflow in the multiplication */
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if (x > 1.0 && y > DBL_MAX/x) {
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errno = ERANGE;
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return result_neg ? -HUGE_VAL : HUGE_VAL;
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}
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x = exp(x * y);
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return result_neg ? -x : x;
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}
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