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WebSVN – planix.SVN – Blame – /os/branches/feature_tlsv12/sys/src/libc/port/exp.c – Rev 2

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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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#include <u.h>
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#include <libc.h>
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#define	p0  .2080384346694663001443843411e7
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#define	p1  .3028697169744036299076048876e5
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#define	p2  .6061485330061080841615584556e2
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#define	q0  .6002720360238832528230907598e7
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#define	q1  .3277251518082914423057964422e6
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#define	q2  .1749287689093076403844945335e4
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#define	log2e  1.4426950408889634073599247
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#define	sqrt2  1.4142135623730950488016887
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#define	maxf  10000
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double
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exp(double arg)
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{
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	double fract, 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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		return Inf(1);
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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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}