gammln.c

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#include <math.h>
 
float gammln(float xx) {
    double x, y, tmp, ser;
    static double cof[6] = {76.18009172947146, -86.50532032941677,
        24.01409824083091, -1.231739572450155,
        0.1208650973866179e-2, -0.5395239384953e-5};
    int j;
 
    y = x = xx;
    tmp = x + 5.5;
    tmp -= (x + 0.5) * log(tmp);
    ser = 1.000000000190015;
    for (j = 0; j <= 5; j++) ser += cof[j] / ++y;
    return -tmp + log(2.5066282746310005 * ser / x);
}