How to count character occurrences using SIMD

Question

I am given a array of lowercase characters (up to 1.5Gb) and a character c. And I want to find how many occurrences are of the character c using AVX instructions.

Answer 1

If you don't insist on using only SIMD instructions, you can make use
of the VPMOVMSKB instruction in combination with the POPCNT instruction. The former combines the highest bits of each byte into a 32-bit integer mask and the latter counts the 1 bits in this integer (=the count of char matches).

int couter=0;
for(i=0; i

I haven't tested this solution, but you should get the gist.