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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