Use _mm_extract_epi16 to extract the mask

[ghost]

(V)PCMPESTRM places a mask word into XMM0. We only need to extract the low order 16 bits, and not the low order 32 bits.

There doesn't appear to be an impact on the compiled assembly; however, PEXTRD is an SSE4.1 feature whereas PEXTRW is SSE2.

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[shepmaster]

PEXTRD is an SSE4.1 feature whereas PEXTRW is SSE2.

Isn't PCMPESTRM SSE4.2 anyway, so this point is rather moot? I still like it because it's more closely aligned to the desired semantics,

[ghost]

Yes, PCMPESTRM is SSE4.2, so the SSE2 vs. SSE4.1 difference is likely moot. One question in my mind is whether a processor supporting SSE4.2 is guaranteed to support the earlier versions SSE4.1, SSE3, SSE2, and SSE. From cursory research, the answer seems to be "yes"; however, I have yet to see where this is guaranteed:

• https://superuser.com/questions/137172/sse2-sse4-2-compatibility
• https://stackoverflow.com/questions/49157522/does-a-processor-that-supports-sse4-support-ssse3-instructions
• https://stackoverflow.com/questions/30355620/are-older-simd-versions-available-when-using-newer-ones

[shepmaster]

whether a processor supporting SSE4.2 is guaranteed to support the earlier versions

If we wanted to be paranoid, we could require all of the intrinsic families we need. I expect a failure here will end in a compilation error though, so I'm willing to wait for that.