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

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 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/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/intrinsics/intrinsics-for-intel-advanced-vector-extensions/intrinsics-for-packed-test-operations/mm256-testz-si256.html https://www.intel.com/content/www/us/en/develop/documentatio...