#include <stdio.h>

#ifndef CHECK_TYPE
#  define CHECK_TYPE unsigned long
#endif

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

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