56 lines
1.4 KiB
C
56 lines
1.4 KiB
C
#include <stdio.h>
|
|
#include <limits.h>
|
|
|
|
/* Original code copied from
|
|
http://rosettacode.org/wiki/Evaluate_binomial_coefficients
|
|
*/
|
|
|
|
/* We go to some effort to handle overflow situations */
|
|
|
|
static unsigned long long gcd_ui(unsigned long long x, unsigned long long y) {
|
|
unsigned long long t;
|
|
if (y < x) { t = x; x = y; y = t; }
|
|
while (y > 0) {
|
|
t = y; y = x % y; x = t; /* y1 <- x0 % y0 ; x1 <- y0 */
|
|
}
|
|
return x;
|
|
}
|
|
|
|
unsigned long long binomial(unsigned long long n, unsigned long long k) {
|
|
unsigned long long d, g, r = 1;
|
|
if (k == 0) return 1;
|
|
if (k == 1) return n;
|
|
if (k >= n) return (k == n);
|
|
if (k > n/2) k = n-k;
|
|
for (d = 1; d <= k; d++) {
|
|
if (r >= ULLONG_MAX/n) { /* Possible overflow */
|
|
unsigned long long nr, dr; /* reduced numerator / denominator */
|
|
g = gcd_ui(n, d); nr = n/g; dr = d/g;
|
|
g = gcd_ui(r, dr); r = r/g; dr = dr/g;
|
|
if (r >= ULLONG_MAX/nr) return 0; /* Unavoidable overflow */
|
|
r *= nr;
|
|
r /= dr;
|
|
n--;
|
|
} else {
|
|
r *= n--;
|
|
r /= d;
|
|
}
|
|
}
|
|
return r;
|
|
}
|
|
|
|
unsigned long long binomial_(int *n, int *k)
|
|
{
|
|
// printf("n=%d k=%d %lu\n",*n,*k,binomial(*n,*k));
|
|
return binomial(*n,*k);
|
|
}
|
|
|
|
double hypergeo_(int *x, int *NN, int *XX, int *s)
|
|
{
|
|
double a,b,c;
|
|
a=(double)binomial(*XX, *x);
|
|
b=(double)binomial(*NN-*XX, *s-*x);
|
|
c=(double)binomial(*NN, *s);
|
|
return a*b/c;
|
|
}
|