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Annotation of 43BSDReno/lib/libm/common_source/erf.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1985 Regents of the University of California.
                      3:  * All rights reserved.  The Berkeley software License Agreement
                      4:  * specifies the terms and conditions for redistribution.
                      5:  */
                      6: 
                      7: #ifndef lint
                      8: static char sccsid[] = "@(#)erf.c      5.2 (Berkeley) 4/29/88";
                      9: #endif /* not lint */
                     10: 
                     11: /*
                     12:        C program for floating point error function
                     13: 
                     14:        erf(x) returns the error function of its argument
                     15:        erfc(x) returns 1.0-erf(x)
                     16: 
                     17:        erf(x) is defined by
                     18:        ${2 over sqrt(pi)} int from 0 to x e sup {-t sup 2} dt$
                     19: 
                     20:        the entry for erfc is provided because of the
                     21:        extreme loss of relative accuracy if erf(x) is
                     22:        called for large x and the result subtracted
                     23:        from 1. (e.g. for x= 10, 12 places are lost).
                     24: 
                     25:        There are no error returns.
                     26: 
                     27:        Calls exp.
                     28: 
                     29:        Coefficients for large x are #5667 from Hart & Cheney (18.72D).
                     30: */
                     31: 
                     32: #define M 7
                     33: #define N 9
                     34: static double torp = 1.1283791670955125738961589031;
                     35: static double p1[] = {
                     36:        0.804373630960840172832162e5,
                     37:        0.740407142710151470082064e4,
                     38:        0.301782788536507577809226e4,
                     39:        0.380140318123903008244444e2,
                     40:        0.143383842191748205576712e2,
                     41:        -.288805137207594084924010e0,
                     42:        0.007547728033418631287834e0,
                     43: };
                     44: static double q1[]  = {
                     45:        0.804373630960840172826266e5,
                     46:        0.342165257924628539769006e5,
                     47:        0.637960017324428279487120e4,
                     48:        0.658070155459240506326937e3,
                     49:        0.380190713951939403753468e2,
                     50:        0.100000000000000000000000e1,
                     51:        0.0,
                     52: };
                     53: static double p2[]  = {
                     54:        0.18263348842295112592168999e4,
                     55:        0.28980293292167655611275846e4,
                     56:        0.2320439590251635247384768711e4,
                     57:        0.1143262070703886173606073338e4,
                     58:        0.3685196154710010637133875746e3,
                     59:        0.7708161730368428609781633646e2,
                     60:        0.9675807882987265400604202961e1,
                     61:        0.5641877825507397413087057563e0,
                     62:        0.0,
                     63: };
                     64: static double q2[]  = {
                     65:        0.18263348842295112595576438e4,
                     66:        0.495882756472114071495438422e4,
                     67:        0.60895424232724435504633068e4,
                     68:        0.4429612803883682726711528526e4,
                     69:        0.2094384367789539593790281779e4,
                     70:        0.6617361207107653469211984771e3,
                     71:        0.1371255960500622202878443578e3,
                     72:        0.1714980943627607849376131193e2,
                     73:        1.0,
                     74: };
                     75: 
                     76: double
                     77: erf(arg) double arg;{
                     78:        double erfc();
                     79:        int sign;
                     80:        double argsq;
                     81:        double d, n;
                     82:        int i;
                     83: 
                     84:        sign = 1;
                     85:        if(arg < 0.){
                     86:                arg = -arg;
                     87:                sign = -1;
                     88:        }
                     89:        if(arg < 0.5){
                     90:                argsq = arg*arg;
                     91:                for(n=0,d=0,i=M-1; i>=0; i--){
                     92:                        n = n*argsq + p1[i];
                     93:                        d = d*argsq + q1[i];
                     94:                }
                     95:                return(sign*torp*arg*n/d);
                     96:        }
                     97:        if(arg >= 10.)
                     98:                return(sign*1.);
                     99:        return(sign*(1. - erfc(arg)));
                    100: }
                    101: 
                    102: double
                    103: erfc(arg) double arg;{
                    104:        double erf();
                    105:        double exp();
                    106:        double n, d;
                    107:        int i;
                    108: 
                    109:        if(arg < 0.)
                    110:                return(2. - erfc(-arg));
                    111: /*
                    112:        if(arg < 0.5)
                    113:                return(1. - erf(arg));
                    114: */
                    115:        if(arg >= 10.)
                    116:                return(0.);
                    117: 
                    118:        for(n=0,d=0,i=N-1; i>=0; i--){
                    119:                n = n*arg + p2[i];
                    120:                d = d*arg + q2[i];
                    121:        }
                    122:        return(exp(-arg*arg)*n/d);
                    123: }

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