I think when I looked single instr crc32 was ~5 times faster than the pclmulqdq version.<p>As an aside, if they have a server in production that doesn&#x27;t support CLMUL, they should junk that machine - it appeared in Westmere and Bulldozer - everything earlier is EOLed. Crc32 was in sse4.2, so Nehalem.<p>The crc32 instruction is hard to beat, has been around for years, and I would guess the different poly could be phased in on their systems like you would for changing a password algorithm, or just try the new poly since it is quick, and if it fails use the old poly.