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The previous implementation of CRC32C on x86 relied on the native CRC32 instruction from the SSE 4.2 extension, which operates on up to 8 bytes at a time. We can get a substantial speedup by using carryless multiplication on SIMD registers, processing 64 bytes per loop iteration. Shorter inputs fall back to ordinary CRC instructions. On Intel Tiger Lake hardware (2020), CRC is now 50% faster for inputs between 64 and 112 bytes, and 3x faster for 256 bytes. The VPCLMULQDQ instruction on 512-bit registers has been available on Intel hardware since 2019 and AMD since 2022. There is an older variant for 128-bit registers, but at least on Zen 2 it performs worse than normal CRC instructions for short inputs. We must now do a runtime check, even for builds that target SSE 4.2. This doesn't matter in practice for WAL (arguably the most critical case), because since commit e2809e3a1 the final computation with the 20-byte WAL header is inlined and unrolled when targeting that extension. Compared with two direct function calls, testing showed equal or slightly faster performance in performing an indirect function call on several dozen bytes followed by inlined instructions on constant input of 20 bytes. The MIT-licensed implementation was generated with the "generate" program from https://github.com/corsix/fast-crc32/ Based on: "Fast CRC Computation for Generic Polynomials Using PCLMULQDQ Instruction" V. Gopal, E. Ozturk, et al., 2009 Co-authored-by: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com> Co-authored-by: Paul Amonson <paul.d.amonson@intel.com> Reviewed-by: Nathan Bossart <nathandbossart@gmail.com> Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version) Reviewed-by: Matthew Sterrett <matthewsterrett2@gmail.com> (earlier version) Tested-by: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com> Tested-by: David Rowley <<dgrowleyml@gmail.com>> (earlier version) Discussion: https://postgr.es/m/BL1PR11MB530401FA7E9B1CA432CF9DC3DC192@BL1PR11MB5304.namprd11.prod.outlook.com Discussion: https://postgr.es/m/PH8PR11MB82869FF741DFA4E9A029FF13FBF72@PH8PR11MB8286.namprd11.prod.outlook.com