Always check user input.

crackit.md

First thing, line 14:

countOnThreads(atoi(argv[1]), threads, ^(CFTimeInterval seconds, unsigned long long check, unsigned int threads) {

atoi(argv[1]) is left unchecked allowing unexpected input like negative numbers which would be interpreted as a big positive number once passed to countOnThreads.

Then, passing "-1" as the second argument to main() makes atoi() return -1 which is then converted to UINT_MAX. Assuming that the first argument is valid and positive, lets continue.

Line 12:

if (argv[2]) threads = atoi(argv[2]);

Line 18:

unsigned const long long execPer = max/threads;

Both max and threads are integer types, so if threads is bigger than max, execPer will be 0.

Here is where it gets nasty.

Line 23:

for (int increment = 0; increment < threads; increment++) {

This loop will run UINT_MAX times.

Line 28:

while (counter < execPer) counter++;

Will never run since counter is equal to execPer, so counter will still be 0.

Line 34:

if (numberOfExecutions == threads) {

This will be equal when the loop has ran UINT_MAX times.

Line 36:

unsigned long long fixMod = execPer*threads;
while (fixMod < max) fixMod++;

fixMod will be 0 because 0 * UINT_MAX is 0. The loop will run max times.

So, the for loop will run UINT_MAX times, the first while loop will never run and the last while loop will run max times.