factorial.c

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <factorial.h>

/* Calculates max and allocate table. Returns !0 if
 * memory could not be allocated.
 */

int factorial_table_init(factorial_table *t)
{
    unsigned i, factorial;

    t->max = factorial = 1;
    while (INT_MAX / factorial > t->max + 1)
        factorial *= ++t->max;
    t->table = malloc((t->max + 1)*sizeof(unsigned));
    if (!t->table) return !0;
    t->table[0] = 1;
    for (i = 1; i <= t->max; i++)
        t->table[i] = i * t->table[i-1];
    fprintf(stdout,"A factorial table was just allocated.\n");
    return 0;
}

/* Uses a table to get the factorial of an integer number n. Returns
 * (-1) if n is negative and (-2) if n is too big.
 */

int factorial_get(factorial_table *t, int n)
{
    if (n < 0) return (-1);    
    if (n > t->max) return (-2);
    return t->table[n];
}

/* Frees the table we used. */

void factorial_table_free(factorial_table *t)
{
    free(t->table);
    fprintf(stdout,"A factorial table was just freed.\n");
}