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Modern x86 and x86-64 processors with SSE 4.2 support have special instructions, crc32b and crc32q, for calculating CRC-32C. They greatly speed up CRC calculation. Whether the instructions can be used or not depends on the compiler and the target architecture. If generation of SSE 4.2 instructions is allowed for the target (-msse4.2 flag on gcc and clang), use them. If they are not allowed by default, but the compiler supports the -msse4.2 flag to enable them, compile just the CRC-32C function with -msse4.2 flag, and check at runtime whether the processor we're running on supports it. If it doesn't, fall back to the slicing-by-8 algorithm. (With the common defaults on current operating systems, the runtime-check variant is what you get in practice.) Abhijit Menon-Sen, heavily modified by me, reviewed by Andres Freund.
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.