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Currently mul_var() uses the schoolbook multiplication algorithm, which is O(n^2) in the number of NBASE digits. To improve performance for large inputs, convert the inputs to base NBASE^2 before multiplying, which effectively halves the number of digits in each input, theoretically speeding up the computation by a factor of 4. In practice, the actual speedup for large inputs varies between around 3 and 6 times, depending on the system and compiler used. In turn, this significantly reduces the runtime of the numeric_big regression test. For this to work, 64-bit integers are required for the products of base-NBASE^2 digits, so this works best on 64-bit machines, on which it is faster whenever the shorter input has more than 4 or 5 NBASE digits. On 32-bit machines, the additional overheads, especially during carry propagation and the final conversion back to base-NBASE, are significantly higher, and it is only faster when the shorter input has more than around 50 NBASE digits. When the shorter input has more than 6 NBASE digits (so that mul_var_short() cannot be used), but fewer than around 50 NBASE digits, there may be a noticeable slowdown on 32-bit machines. That seems to be an acceptable tradeoff, given the performance gains for other inputs, and the effort that would be required to maintain code specifically targeting 32-bit machines. Joel Jacobson and Dean Rasheed. Discussion: https://postgr.es/m/9d8a4a42-c354-41f3-bbf3-199e1957db97%40app.fastmail.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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.