factorial.h

/* A table of factorials. table[i] is the factorial of i. The
 * max field is calculated so that its factorial would not be an
 * integer overflow.
 */

typedef struct {
    unsigned max;
    unsigned *table;
} factorial_table;

int factorial_table_init(factorial_table *t);
int factorial_get(factorial_table *t, int n);
void factorial_table_free(factorial_table *t);