6b423ec677
Experiments have shown that modern versions of both gcc and clang are unable to fully optimize the multiplication by 10 that we're doing in the pg_strtointNN functions. Both compilers seem to be making use of "imul", which is not the most efficient way to multiply by 10. This seems to be due to the overflow checking that we're doing. Without the overflow checks, both those compilers switch to a more efficient method of multiplying by 10. In absence of overflow concern, integer multiplication by 10 can be done by bit-shifting left 3 places to multiply by 8 and then adding the original value twice. To allow compilers this flexibility, here we adjust the code so that we accumulate the number as an unsigned version of the type and remove the use of pg_mul_sNN_overflow() and pg_sub_sNN_overflow(). The overflow checking can be done simply by checking if the accumulated value has gone beyond a 10th of the maximum *signed* value for the given type. If it has then the accumulation of the next digit will cause an overflow. After this is done, we do a final overflow check before converting the unsigned version of the number back to its signed counterpart. Testing has shown about an 8% speedup of a COPY into a table containing 2 INT columns. Author: David Rowley, Dean Rasheed Discussion: https://postgr.es/m/CAApHDvrL6_+wKgPqRHr7gH_6xy3hXM6a3QCsZ5ForurjDFfenA@mail.gmail.com Discussion: https://postgr.es/m/CAApHDvrdYByjfj-=WbmVNFgmVZg88-dE7heukw8p55aJ+W=qxQ@mail.gmail.com |
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README
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/.