I have tried this on a couple of different machines. On one machine it gives ridiculous answers like you found. On the other it at least works as expected, although it's kinda useless since it doesn't print the matched lines.

On the working machine it reported using SSE4.2 acceleration while the broken one used AVX2 acceleration. However, the machine using SSE4.2 didn't see nearly as much speedup as the AVX2 machine. Regular system grep on the SSE4.2 machine took 0.186 seconds to do the search, while krep needed 0.154 seconds. However the biggest test file I had handy was only 123MB, so maybe the lead will grow more with a larger file?