#include <stdio.h>

#ifndef CHECK_TYPE
#  define CHECK_TYPE unsigned long
#endif

int overflowed(CHECK_TYPE number, CHECK_TYPE inc, int sign) {
    CHECK_TYPE sum = number + inc;
    if (sign > 0 && sum <= number)  /* incrementing does not increase value */
        return 1;
    if (sign < 0 && sum >= number)  /* decrementing does not decrease value */
        return 1;
    return 0;
}

CHECK_TYPE find_limit(int sign) {
    CHECK_TYPE number, inc = sign;
    for (number = 0;
         !overflowed(number, inc, sign);
         number += inc,
         inc += number / 4);
    /* now (number + inc) gives overflow of checked type */
    for ( ; (sign > 0 && inc > 1) || (sign < 0 && inc < -1); ) {
        if (overflowed(number, inc/2, sign))
            inc = inc/2;
        else
            number += inc/2;
    }
    return number;
}

int main() {
    int size = sizeof(CHECK_TYPE);
    printf("Size of type: %d byte(s)\n", size);
    printf("Supposed upper limit: %llu (signed) or %llu (unsigned)\n",
           (1LL << (size * 8 - 1)) - 1LL, (1LL << (size * 8 - 1))*2LL - 1LL);
    printf("Supposed lower limit: %lld (signed) or %lld (unsigned)\n",
           -(1LL << (size * 8 - 1)), 0LL);
    printf("Calculated upper limit: %llu\n", (unsigned long long)find_limit(1));
    printf("Calculated lower limit: %lld\n", (long long)find_limit(-1));
    return 0;
}