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The cash_div_intX functions applied rint() to the result of the division. That's not merely useless (because the result is already an integer) but it causes precision loss for values larger than 2^52 or so, because of the forced conversion to float8. On the other hand, the cash_mul_fltX functions neglected to apply rint() to their multiplication results, thus possibly causing off-by-one outputs. Per C standard, arithmetic between any integral value and a float value is performed in float format. Thus, cash_mul_flt4 and cash_div_flt4 produced answers good to only about six digits, even when the float value is exact. We can improve matters noticeably by widening the float inputs to double. (It's tempting to consider using "long double" arithmetic if available, but that's probably too much of a stretch for a back-patched fix.) Also, document that cash_div_intX operators truncate rather than round. Per bug #14663 from Richard Pistole. Back-patch to all supported branches. Discussion: https://postgr.es/m/22403.1495223615@sss.pgh.pa.us |
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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/.