http://article.gmane.org/gmane.comp.multimedia.puredata.general/56291/match=div+mod
On Saturday, May 7, 2016 11:45 PM, Alexandre Torres Porres
<[email protected]> wrote:
On Sat, May 7, 2016 at 6:44 PM, Miller Puckette <[email protected]> wrote:
I _think_ (but am not sure) that "%" works differently on different
CPU architectures.
2016-05-07 20:20 GMT-03:00 Matt Barber <[email protected]>:
% can be different with respect to sign in different implementations of C.
fmod() in C is designed to work with floats.
Wow, so using "%" in a source code can generate different results in different
CPU architectures?
that's interesting... Can we confirm that? And, if so, why?
And how about fmod? Sames as %? By the way, the [%~] (or [modulo~] object -
also present in cyclone - uses "fmod". And "fmod" in expr family also uses
fmod...
But anyway [%], [mod] and "%" in [expr] use the "%" operation in the C code...
On my system, -10 [mod 3] and -10 [% 3] in Pd work differently. [mod] outputs
the positive remainder, which is 2, while % outputs the remainder with the sign
of the dividend, which is -1.
I also get that, and I'm on a mac intel... and this behaviour with the [%]
object is what you get if you are using a code in C with "fmod"... (%~ and
"fmod" in expr).
And well, looking at the source code in x_arithmetic.c, both % and mod rely on
the "%" operation in the C code, but [mod] turns the input negative values into
positive input values
"if (n2 < 0) n2 = -n2;"
[%] and [expr $f1 % $f2] use "%" in the C code without turning negative input
to positive input, so the results are the same. I'm getting the same behaviour
as Matt, but if there's this deal with different results depending on
architecture, then % in [expr] is subject to the same effect.
But anyway, again, comparing to others in Pd and Max, it seems like the [mod]
object is the odd one out, where it converts negative input to positive input
on purpose. Lets say it has this behaviour intentionally, but also that we
could keep [%] with this other intentional behaviour.
If the way things are coded makes it undefined or dependent on CPU
architecture, then it's a bug and we could force it to behave always in the way
where -10 [% 3] gives "-1".
cheers
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