Re: BUG in postgres mathematic

Notice how the INT4 rounding is banker's rounding (round to the nearest even
number).  That is what we would want the INT8 to do as well, not just a
simple round like I mentioned before. Again, the INT8 shows truncation.  I've
been looking around the source code, but I can't see where all this
happens.

reaster=# SELECT 1.5::FLOAT::INT4;
 ?column?
----------
        2
(1 row)

reaster=# SELECT 2.5::FLOAT::INT4;
 ?column?
----------
        2
(1 row)

reaster=# SELECT 1.5::FLOAT::INT8;
 ?column?
----------
        1
(1 row)

reaster=# SELECT 2.5::FLOAT::INT8;
 ?column?
----------
        2
(1 row)


On Thursday 25 January 2001 22:52, Tom Lane wrote:
> "Robert B. Easter" <reaster@comptechnews.com> writes:
> > This problem is not specific to Postgres.
>
> The fact that 5*27.81*100 != 27.81*100*5 is certainly a garden-variety
> floating-point roundoff error.  However, I think Max has a fair
> complaint here: it seems float-to-int8 conversion is truncating, not
> rounding like the other conversions to integer do.
>
> regression=# select 4.7::float8::int4;
>  ?column?
> ----------
>         5
> (1 row)
>
> regression=# select 4.7::float8::int8;
>  ?column?
> ----------
>         4
> (1 row)
>
> Seems to me this is a bug we should fix.
>
>             regards, tom lane

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