On Sat, May 7, 2016 at 6:44 PM, Miller Puckette msp@ucsd.edu wrote:
I _think_ (but am not sure) that "%" works differently on different CPU architectures.
2016-05-07 20:20 GMT-03:00 Matt Barber brbrofsvl@gmail.com:
% 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
http://article.gmane.org/gmane.comp.multimedia.puredata.general/56291/match=...
On Saturday, May 7, 2016 11:45 PM, Alexandre Torres Porres <porres@gmail.com> wrote:
On Sat, May 7, 2016 at 6:44 PM, Miller Puckette msp@ucsd.edu wrote:
I _think_ (but am not sure) that "%" works differently on different CPU architectures.
2016-05-07 20:20 GMT-03:00 Matt Barber brbrofsvl@gmail.com:
% 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 _______________________________________________ Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
cool, yeah, i fugured there was a reason for mod to be coded the way it is
but I'm more concerned on how "%" could be unreliable... or even "fmod"?
cheers
2016-05-08 1:01 GMT-03:00 Jonathan Wilkes jancsika@yahoo.com:
http://article.gmane.org/gmane.comp.multimedia.puredata.general/56291/match=...
On Saturday, May 7, 2016 11:45 PM, Alexandre Torres Porres < porres@gmail.com> wrote:
On Sat, May 7, 2016 at 6:44 PM, Miller Puckette msp@ucsd.edu wrote:
I _think_ (but am not sure) that "%" works differently on different CPU architectures.
2016-05-07 20:20 GMT-03:00 Matt Barber brbrofsvl@gmail.com:
% 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
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
HAH, % in SuperCollider will work as [mod] in Pd
-7 % 5 gives us -3
2016-05-08 1:09 GMT-03:00 Alexandre Torres Porres porres@gmail.com:
cool, yeah, i fugured there was a reason for mod to be coded the way it is
but I'm more concerned on how "%" could be unreliable... or even "fmod"?
cheers
2016-05-08 1:01 GMT-03:00 Jonathan Wilkes jancsika@yahoo.com:
http://article.gmane.org/gmane.comp.multimedia.puredata.general/56291/match=...
On Saturday, May 7, 2016 11:45 PM, Alexandre Torres Porres < porres@gmail.com> wrote:
On Sat, May 7, 2016 at 6:44 PM, Miller Puckette msp@ucsd.edu wrote:
I _think_ (but am not sure) that "%" works differently on different CPU architectures.
2016-05-07 20:20 GMT-03:00 Matt Barber brbrofsvl@gmail.com:
% 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
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
fmod() is a c function with a consistent definition:
http://en.cppreference.com/w/c/numeric/math/fmod
If I remember correctly, the % operator result can take the sign of its dividend, but it does not have to; it is implementation specific. Likewise integer division using / is implementation specific (truncation vs. flooring), but I believe it is guaranteed to be consistent with %. Hence the rationale for div().
On Sun, May 8, 2016 at 12:09 AM, Alexandre Torres Porres porres@gmail.com wrote:
cool, yeah, i fugured there was a reason for mod to be coded the way it is
but I'm more concerned on how "%" could be unreliable... or even "fmod"?
cheers
2016-05-08 1:01 GMT-03:00 Jonathan Wilkes jancsika@yahoo.com:
http://article.gmane.org/gmane.comp.multimedia.puredata.general/56291/match=...
On Saturday, May 7, 2016 11:45 PM, Alexandre Torres Porres < porres@gmail.com> wrote:
On Sat, May 7, 2016 at 6:44 PM, Miller Puckette msp@ucsd.edu wrote:
I _think_ (but am not sure) that "%" works differently on different CPU architectures.
2016-05-07 20:20 GMT-03:00 Matt Barber brbrofsvl@gmail.com:
% 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
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
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Alexandre Torres Porres -
Jonathan Wilkes -
Matt Barber