/*	@(#)erf.c	1.9	*//*LINTLIBRARY*//* *	erf returns the error function of its double-precision argument. *	erfc(x) returns 1 - erf(x). * *	erf(x) is defined by *	${2 over sqrt pi} int from 0 to x e sup {- t sup 2} dt$. * *	The entry for erfc is provided because of the *	extreme loss of relative accuracy if erf(x) is *	called for large x and the result subtracted *	from 1 (e.g. for x = 5, 12 places are lost). * *	There are no error returns. * *	Calls exp for |x| > 0.5. * *	Coefficients for large x are #5667 from Hart & Cheney (18.72D). */#include <math.h>/* approx sqrt(log(MAXDOUBLE)) */#if u3b#define MAXVAL	27.23#else#define MAXVAL	 9.27#endif#define DPOLYD(y, p, q)	for (n = d = 0, i = sizeof(p)/sizeof(p[0]); --i >= 0; ) \				{ n = n * y + p[i]; d = d * y + q[i]; }static double p1[] = {	0.804373630960840172832162e5,	0.740407142710151470082064e4,	0.301782788536507577809226e4,	0.380140318123903008244444e2,	0.143383842191748205576712e2,	-.288805137207594084924010e0,	0.007547728033418631287834e0,}, q1[]  = {	0.804373630960840172826266e5,	0.342165257924628539769006e5,	0.637960017324428279487120e4,	0.658070155459240506326937e3,	0.380190713951939403753468e2,	1.0,	0.0,};static double p2[]  = {	0.18263348842295112592168999e4,	0.28980293292167655611275846e4,	0.2320439590251635247384768711e4,	0.1143262070703886173606073338e4,	0.3685196154710010637133875746e3,	0.7708161730368428609781633646e2,	0.9675807882987265400604202961e1,	0.5641877825507397413087057563e0,	0.0,}, q2[]  = {	0.18263348842295112595576438e4,	0.495882756472114071495438422e4,	0.60895424232724435504633068e4,	0.4429612803883682726711528526e4,	0.2094384367789539593790281779e4,	0.6617361207107653469211984771e3,	0.1371255960500622202878443578e3,	0.1714980943627607849376131193e2,	1.0,};doubleerf(x)register double x;{	int neg = 0;	if (x < 0) {		x = -x;		neg++;	}	if (x > 0.5)		x = 1 - erfc(x);	else {		register double n, d, xsq = x * x;		register int i;		DPOLYD(xsq, p1, q1);		x *= M_2_SQRTPI * n/d;	}	return (neg ? -x : x);}doubleerfc(x)register double x;{	register double n, d;	register int i;	if (x < 0.5)		return (1 - erf(x));	if (x >= MAXVAL) /* exp(-x * x) sure to underflow */		return (0.0);	DPOLYD(x, p2, q2);	return (exp(-x * x) * n/d);}