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Use __builtin_clz() where available. Where it isn't, we can still win a little by using the pg_leftmost_one_pos[] lookup table instead of having a private table. Also drop the initial right shift by ALLOC_MINBITS in favor of subtracting ALLOC_MINBITS from the leftmost-one-pos result. This is a win because the compiler can fold that adjustment into other constants it'd have to add anyway, making the shift-removal free. Also, we can explain this coding as an unrolled form of pg_leftmost_one_pos32(), even though that's a bit ahistorical since it long predates pg_bitutils.h. John Naylor, with some cosmetic adjustments by me Discussion: https://postgr.es/m/CACPNZCuNUGMxjK7WTn_=WZnRbfASDdBxmjsVf2+m9MdmeNw_sg@mail.gmail.com
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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.