Factorial using __int128 integer

fact128.c

#include <stdio.h>

typedef unsigned __int128 uint128;

/* printing 128-bit value isn't official support yet
   so here's implementation of converting 128-bit value into string */
char *str_uint128(uint128 n)
{
    /* got confused about arithmetic operation with '0'? read more about ascii :) */
    static char buf[1000] = {0}, *buft = buf;
    int nbuf = 1000;

    if (n == 0)
        *buft = '0'; // obviously
    else for(buft += nbuf - 2; n > 0; n /= 10) // ever heard else-for? ;)
            *--buft = '0' + (n % 10);

    return buft;
}

uint128 fact(int N) // calculate factorial with O(n)
{
    uint128 n, i;
    for(n = i = 1; i <= N; i++)
        n *= i;
    return n;
}

int main()
{
    printf("%d! -> %s\n", 5, str_uint128(fact(5)));
    printf("%d! -> %s\n", 10, str_uint128(fact(10)));
    printf("%d! -> %s\n", 15, str_uint128(fact(15)));
}

nice job 👍

i tried implementing your function to get a string out of an unsigned __int128, but it only outputs 32 digits as the max value..? (i know there is no max value for this in limits.h, i calculated it myself subtracting 1 from 0)

hi @alletsbckwrds, i tried to reproduce but so far i got the expected value. see here: https://godbolt.org/z/xaM8h16vn
do you any example in code that i can use for testing?

oops my bad

…

On Sun, 9 Oct 2022, 04:15 Mohd Shahril, ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ hi @alletsbckwrds <https://github.com/alletsbckwrds>, i tried to reproduce but so far i got the expected value. see here: https://godbolt.org/z/xaM8h16vn do you any example in code that i can use for testing? — Reply to this email directly, view it on GitHub <https://gist.github.com/08ce05ca880b6e6d4e5d#gistcomment-4328822>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ALS23AKWHC73GJ6X57IAGG3WCITFPANCNFSM44KU5PPA> . You are receiving this because you were mentioned.Message ID: ***@***.***>