69 lines
1.3 KiB
C
69 lines
1.3 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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/* $Header$ */
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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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exp(double x)
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{
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/* Algorithm and coefficients from:
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"Software manual for the elementary functions"
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by W.J. Cody and W. Waite, Prentice-Hall, 1980
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*/
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static double p[] = {
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0.25000000000000000000e+0,
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0.75753180159422776666e-2,
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0.31555192765684646356e-4
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};
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static double q[] = {
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0.50000000000000000000e+0,
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0.56817302698551221787e-1,
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0.63121894374398503557e-3,
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0.75104028399870046114e-6
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};
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double xn, g;
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int n;
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int negative = x < 0;
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if (x < M_LN_MIN_D) {
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errno = ERANGE;
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return 0.0;
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}
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if (x > M_LN_MAX_D) {
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errno = ERANGE;
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return HUGE_VAL;
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}
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if (negative) x = -x;
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/* ??? avoid underflow ??? */
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n = x * M_LOG2E + 0.5; /* 1/ln(2) = log2(e), 0.5 added for rounding */
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xn = n;
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{
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double x1 = (long) x;
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double x2 = x - x1;
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g = ((x1-xn*0.693359375)+x2) - xn*(-2.1219444005469058277e-4);
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}
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if (negative) {
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g = -g;
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n = -n;
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}
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xn = g * g;
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x = g * POLYNOM2(xn, p);
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n += 1;
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return (ldexp(0.5 + x/(POLYNOM3(xn, q) - x), n));
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}
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