124 lines
2.2 KiB
C
124 lines
2.2 KiB
C
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/*
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* (c) copyright 1983 by the Vrije Universiteit, Amsterdam, The Netherlands.
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*
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* This product is part of the Amsterdam Compiler Kit.
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*
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* Permission to use, sell, duplicate or disclose this software must be
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* obtained in writing. Requests for such permissions may be sent to
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*
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* Dr. Andrew S. Tanenbaum
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* Wiskundig Seminarium
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* Vrije Universiteit
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* Postbox 7161
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* 1007 MC Amsterdam
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* The Netherlands
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*
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*/
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/* Author: J.W. Stevenson */
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#include <pc_err.h>
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extern double _fif();
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extern double _fef();
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extern _trp();
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/*
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exp returns the exponential function of its
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floating-point argument.
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The coefficients are #1069 from Hart and Cheney. (22.35D)
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*/
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#define HUGE 1.701411733192644270e38
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static double p0 = .2080384346694663001443843411e7;
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static double p1 = .3028697169744036299076048876e5;
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static double p2 = .6061485330061080841615584556e2;
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static double q0 = .6002720360238832528230907598e7;
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static double q1 = .3277251518082914423057964422e6;
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static double q2 = .1749287689093076403844945335e4;
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static double log2e = 1.4426950408889634073599247;
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static double sqrt2 = 1.4142135623730950488016887;
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static double maxf = 10000.0;
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static double
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floor(d)
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double d;
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{
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if (d<0) {
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d = -d;
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if (_fif(d, 1.0, &d) != 0)
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d += 1;
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d = -d;
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} else
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_fif(d, 1.0, &d);
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return(d);
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}
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static double
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ldexp(fr,exp)
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double fr;
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int exp;
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{
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int neg,i;
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neg = 1;
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if (fr < 0) {
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fr = -fr;
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neg = -1;
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}
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fr = _fef(fr, &i);
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/*
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while (fr < 0.5) {
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fr *= 2;
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exp--;
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}
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*/
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exp += i;
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if (exp > 127) {
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_trp(EEXP);
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return(neg * HUGE);
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}
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if (exp < -127)
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return(0);
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while (exp > 14) {
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fr *= (1<<14);
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exp -= 14;
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}
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while (exp < -14) {
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fr /= (1<<14);
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exp += 14;
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}
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if (exp > 0)
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fr *= (1<<exp);
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if (exp < 0)
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fr /= (1<<(-exp));
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return(neg * fr);
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}
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double
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_exp(arg)
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double arg;
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{
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double fract;
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double temp1, temp2, xsq;
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int ent;
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if(arg == 0)
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return(1);
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if(arg < -maxf)
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return(0);
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if(arg > maxf) {
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_trp(EEXP);
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return(HUGE);
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}
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arg *= log2e;
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ent = floor(arg);
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fract = (arg-ent) - 0.5;
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xsq = fract*fract;
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temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
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temp2 = ((xsq+q2)*xsq+q1)*xsq + q0;
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return(ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent));
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}
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