remainder function
 

Does the C++ compiler used for FRC support the REMAINDER operator "x REM y" per IEC 60559

as specified on Page 235 Section 7.12.10.2 of ISO/IEC 9899:TC3 ?



If someone would be willing to test that with y=360

and x values of 179, 180, 181, 359, 721, -1, -179, -180, -359, -361, -721

and post results it would be much appreciated.

Re: remainder function
 

It seems to be defined if you use the C compiler, but not the C++ one. You could use fmod, which has slightly different behavior.

You can test it out here: http://codepad.org/86MlmNXU

Re: remainder function
 

fmod(x,y) is quite different from remainder(x,y)

The 3 columns below are x, remainder(x,360), and fmod(360):

Re: remainder function
 

What's the issue with using the modulus operator instead of the built-in remainder function?

Re: remainder function
 

Are you saying there is a remainder function in the C++ compiler used for FRC?

Re: remainder function
 

It looks like you need to define it using extern "C" for WindRiver to compile it correctly:

Re: remainder function
 

There's definitely a modulus division operator, which amounts to the same thing.

719 % 360 = 359

Re: remainder function
 

Right, but it rounds the same as fmod() (see http://www.gnu.org/software/libc/man...Functions.html). I don't have enough experience to say when this would be more or less useful in practice, but if you DO need it extern "C" seems to be the way to go about it.

Re: remainder function
 

The modulus division operator is *not* the same thing as the remainder function.

remainder(719,360) is -1, not 359.

Look at the definition of the remainder function which I attached to the original post in this thread.

Re: remainder function
 

OK, so do this instead:

Re: remainder function
 

I can see how the remainder function would be useful in certain cases, except that I don't like the name of the function. It's non-intuitive, and the results would surprise many people who look at the code after the original writer. When I think back to when I learned division in elementary school, the remainder of two positive numbers was always positive (or zero). I'm trying to think of what I would have named that function, to be more in line with its return values.

Re: remainder function
 

The "normal" name for this function is drem(), which I think is a contraction of d-something and remainder.

Re: remainder function
 

"Normal" according to whom? Link please.

Re: remainder function
 

"Delta Remainder" sounds cool. At least when I see drem, I would expect slightly different behavior, thus obeying the programming law of Minimize Surprise.

Re: remainder function
 

GNU libc. See the link in my previous post.