Re: dividing money by money

Andy Balholm <andy(at)balholm(dot)com> writes:
> On Jul 15, 2010, at 7:25 PM, Tom Lane wrote:
>> * I didn't like this bit in cash_numeric():
>>
>> result->n_sign_dscale = NUMERIC_SIGN(result) | fpoint;
>>
>> Not only is that unwarranted chumminess with the implementation of
>> numeric, it's flat-out wrong. If the result isn't exactly the right
>> number of digits (say, it's 12.33999999 instead of the desired 12.34)
>> this just hides the extra digits, it doesn't make the result correct.
>> The right way is to use numeric_round(), which not only sets the dscale
>> where we want it but rounds off any inaccuracy that might have crept in
>> from the division.

> Sorry about that. Is there documentation anywhere for backend
> functions and types?

Nothing at that level of detail, unfortunately, beyond the code itself.
If you'd read the comments near the head of numeric.c, maybe the mistake
would've been apparent to you, or maybe not.

regards, tom lane