Question

What is the best way for pairwise comparison of two integer registers and extraction of equal elements using SSE instructions? For example, if a = [6 4 7 2] and b = [2 4 9 2] (each register contains four 32-bit integers), the result should be [4 2 x x]. An alternative form of this question is how to obtain a binary mask of equal elements (..0101b) that can be used for shuffling or as an index to lookup a parameter for shuffling instruction in the precomputed table.

Answer 1

I would probably use a variant of what drhirsch proposes:

int index = _mm_movemask_ps((__m128)_mm_cmp_epi32(a, b));

This gives you the same index to use in looking up a shuffle mask using only two operations.