Return to gamma.c CVS log

Up to [CSRG BSD Unix] / 43BSD / usr.lib / libom

Annotation of 43BSD/usr.lib/libom/gamma.c, revision 1.1.1.1

1.1       root        1: /*     @(#)gamma.c     4.1     12/25/82        */
                      2: 
                      3: /*
                      4:        C program for floating point log gamma function
                      5: 
                      6:        gamma(x) computes the log of the absolute
                      7:        value of the gamma function.
                      8:        The sign of the gamma function is returned in the
                      9:        external quantity signgam.
                     10: 
                     11:        The coefficients for expansion around zero
                     12:        are #5243 from Hart & Cheney; for expansion
                     13:        around infinity they are #5404.
                     14: 
                     15:        Calls log and sin.
                     16: */
                     17: 
                     18: #include <errno.h>
                     19: #include <math.h>
                     20: 
                     21: int    errno;
                     22: int    signgam = 0;
                     23: static double goobie   = 0.9189385332046727417803297;
                     24: static double pi       = 3.1415926535897932384626434;
                     25: 
                     26: #define M 6
                     27: #define N 8
                     28: static double p1[] = {
                     29:        0.83333333333333101837e-1,
                     30:        -.277777777735865004e-2,
                     31:        0.793650576493454e-3,
                     32:        -.5951896861197e-3,
                     33:        0.83645878922e-3,
                     34:        -.1633436431e-2,
                     35: };
                     36: static double p2[] = {
                     37:        -.42353689509744089647e5,
                     38:        -.20886861789269887364e5,
                     39:        -.87627102978521489560e4,
                     40:        -.20085274013072791214e4,
                     41:        -.43933044406002567613e3,
                     42:        -.50108693752970953015e2,
                     43:        -.67449507245925289918e1,
                     44:        0.0,
                     45: };
                     46: static double q2[] = {
                     47:        -.42353689509744090010e5,
                     48:        -.29803853309256649932e4,
                     49:        0.99403074150827709015e4,
                     50:        -.15286072737795220248e4,
                     51:        -.49902852662143904834e3,
                     52:        0.18949823415702801641e3,
                     53:        -.23081551524580124562e2,
                     54:        0.10000000000000000000e1,
                     55: };
                     56: 
                     57: double
                     58: gamma(arg)
                     59: double arg;
                     60: {
                     61:        double log(), pos(), neg(), asym();
                     62: 
                     63:        signgam = 1.;
                     64:        if(arg <= 0.) return(neg(arg));
                     65:        if(arg > 8.) return(asym(arg));
                     66:        return(log(pos(arg)));
                     67: }
                     68: 
                     69: static double
                     70: asym(arg)
                     71: double arg;
                     72: {
                     73:        double log();
                     74:        double n, argsq;
                     75:        int i;
                     76: 
                     77:        argsq = 1./(arg*arg);
                     78:        for(n=0,i=M-1; i>=0; i--){
                     79:                n = n*argsq + p1[i];
                     80:        }
                     81:        return((arg-.5)*log(arg) - arg + goobie + n/arg);
                     82: }
                     83: 
                     84: static double
                     85: neg(arg)
                     86: double arg;
                     87: {
                     88:        double temp;
                     89:        double log(), sin(), pos();
                     90: 
                     91:        arg = -arg;
                     92:        temp = sin(pi*arg);
                     93:        if(temp == 0.) {
                     94:                errno = EDOM;
                     95:                return(HUGE);
                     96:        }
                     97:        if(temp < 0.) temp = -temp;
                     98:        else signgam = -1;
                     99:        return(-log(arg*pos(arg)*temp/pi));
                    100: }
                    101: 
                    102: static double
                    103: pos(arg)
                    104: double arg;
                    105: {
                    106:        double n, d, s;
                    107:        register i;
                    108: 
                    109:        if(arg < 2.) return(pos(arg+1.)/arg);
                    110:        if(arg > 3.) return((arg-1.)*pos(arg-1.));
                    111: 
                    112:        s = arg - 2.;
                    113:        for(n=0,d=0,i=N-1; i>=0; i--){
                    114:                n = n*s + p2[i];
                    115:                d = d*s + q2[i];
                    116:        }
                    117:        return(n/d);
                    118: }

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.