[PD] why does PD round numbers? (in tables, in messageboxes, etc)

katja katjavetter at gmail.com
Mon Apr 9 12:39:29 CEST 2012

On Mon, Apr 9, 2012 at 1:23 AM, Matteo Sisti Sette
<matteosistisette at gmail.com> wrote:
> On 04/08/2012 04:27 PM, katja wrote:
>> I've once compiled (vanilla) Pd with the format specifiers changed to
>> print up to 8 significant digits, and soon found why it is normally
>> done with 6 digits max. You get things like this:
>> 33 * 0.3 = 9.900001
> That is completely unrelated. That is an issue intrinsic in floating point
> numbers.
> Reducing the precision of numbers when writing them to files (or when
> parsing messages or whatever) is an issue in Pd.
> One thing is rounding numbers for _displaying_ them, another thing is
> rounding them when _storing_ them (whether in a file or wherever).

You're right. In Pd however, the format specifier %g is used for
display (except for message boxes), and the same reformatted value is
eventually saved to disk as text. Therefore, changing the format
specifiers affect both representation and storage. The code is just
simplistic on this aspect.

Doing it better would require a lot of modifications, more than
changing some format specifiers. It's a pity we can't see MaxMsp's
code, the issues seem to be neatly solved there, like:

- You can type, use and store very large floats if they are
representable, and if not representable, the nearest representable
value is automatically displayed and stored.

- On the other hand, you can for example create [* 0.01] without it
being changed into [* 0.0999999] which would be the nearest
representable value.

- The representation in a numbox reckons with the size of the numbox,
for example the result of 7.1 - 7 becomes 0.100 if the numbox can only
hold 5 characters (while Pd gives 0.099 in that case).

It seems to me that they have had a thorough discussion on the matter,
decided about what would be most useful in practice, and implemented
it no matter how many conditional checks this would bring into the


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