On Sat, Jan 31, 2009 at 5:43 PM, Aryeh Gregor
<simetrical+wikil...@gmail.com> wrote:
> On Sat, Jan 31, 2009 at 8:33 PM, Robert Rohde <raro...@gmail.com> wrote:
>> This discussion is getting side tracked.
>>
>> The real complaint here is that
>>
>> {{#expr:(0.00007 * 1000 * 1000) mod 1000}} is giving 69 when it should give
>> 70.
>>
>> This is NOT a formatting issue, but rather it is bug in the #expr
>> parser function, presumably caused by some kind of round-off error.
>
> $ php -r 'echo (0.00007 * 1000 * 1000) % 1000 . "\n";'
> 69
> $ php -r 'echo (int)(0.00007 * 10000000) . "\n";'
> 699
>
> The issue is bog-standard floating-point error. If PHP has a decent
> library for exact-precision arithmetic, we could probably use that.
> Otherwise, template programmers will have to learn how floating-point
> numbers work just like all other programmers in the universe.
In r46671 I have added an explicit test for floating point numbers
that are within 1 part in 10^10 of integers before performing
round-off sensitive conversions and comparisons.
This should eliminate these errors in many cases.
-Robert Rohde
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