From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Feng Tian <ftian(at)vitessedata(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Float/Double cast to int |
Date: | 2015-05-21 19:01:25 |
Message-ID: | 32603.1432234885@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Feng Tian <ftian(at)vitessedata(dot)com> writes:
> Here is a query, server was built witch GCC on Linux, AMD64.
> ftian=# select 1.5::int, 1.5::double precision::int, 314.5::int,
> 314.5::double precision::int;
> int4 | int4 | int4 | int4
> ------+------+------+------
> 2 | 2 | 315 | 314
> (1 row)
> I believe this is because rint is broken -- can some expert on IEEE754
> please help confirm that this is a bug?
rint() is doing what the IEEE spec says, ie round to nearest even.
Your third expression is doing numeric-to-int, and that code doesn't
obey the IEEE spec. We've had discussions (not too long ago) about
making these behaviors more consistent, but people seem to be too
afraid of backwards-compatibility problems if we change it.
regards, tom lane
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