I have a sandbox with hundreds of test numbers to exercise the
{delimitnum} template. This template uses the same math-based
functions as {val}. For anyone who has produced improved math
functions, you can examine values on this sandbox that currently
produce rounding errors and test your new math functions. The sandbox
is at the following:
http://en.wikipedia.org/wiki/User:Greg_L/Delimitnum_sandbox
At the very bottom of the page (which loads slowly), is a concise list
of values that all have errors.
It would still be much better if a character-counting parser function
can be made. Then, numbers like {{val|1.4500}} won’t have its two
trailing zeros truncated.
Greg L
On Jan 31, 2009, at 8:02 PM, Robert Rohde wrote:
On Sat, Jan 31, 2009 at 5:43 PM, Aryeh Gregor
<[email protected]> wrote:
> On Sat, Jan 31, 2009 at 8:33 PM, Robert Rohde <[email protected]>
> 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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