use the popcnt instruction or the popcnt intrinsic function.

It counts how many bits are set to 1, you’re looking for 0.

You can also cast it into a uint64_t integer and do an equality test. There might be a way to use fused multiply add.

Also are you mmaping the file so you can just read it directly as a single buffer? You should be able to madvise to free pages after they’ve been checked.

PUSHFB can also be used. http://0x80.pl/articles/sse-popcount.html

Essentially you want to vectorize this tho memcmp may already be vectorized and do the cpu detection.

Edit: also… You should be able to load 15 x 256 bits and then test them. Try VPTEST https://www.intel.com/content/www/us/en/develop/documentatio...