// Factorial.
 
#include <string.h>
#include <errno.h>
#include <stdio.h>
 
int factorial(int n)
{
    if (n < 0)
    {
        errno = EDOM;
        return -1;
    }
 
    int result = 1;
 
    while (n > 1)
    {
        if (__builtin_mul_overflow(n, result, &result))
        {
            errno = ERANGE;
            return -1;
        }
        n -= 1;
    }
    return result;
}
 
int main(void)
{
    for (int i = -1; i < 14; i++)
    {
        int result = factorial(i);
        if (result < 0)
            printf("%2d! : %s\n", i, strerror(errno));
        else
            printf("%2d! = %d\n", i, result);
    }
    return 0;
}

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