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.

Re: remainder function
 

Fails when angle = -359. Doesn't work with floats.

Re: remainder function
 

Would you mind running that and see if it produces the same output as this:

Re: remainder function
 

What about:

Re: remainder function
 

That's not my remainder.

Did you compile and run it ? It doesn't work correctly.

I'm sure that there's a way, with enough conditional logic, to torture fmod() or % into into a remainder* function, but what I am really asking in this thread is

a) does the C++ compiler provided with FRC have the remainder* function, and

b) does it behave like this:


*This* is my remainder:


*per IEC 60559 as specified on Page 235 Section 7.12.10.2 of ISO/IEC 9899:TC3

Re: remainder function
 

If you have a function that works, then use it?

I don't understand your qualm?

I have not ever encountered a programming scenario where modulus division didn't solve my desire for a remainder, so I'm a bit lost.

If there doesn't exist an operator that does what you want, then you need to either a) fabricate a solution from the operators you have access to, or b) find a library that does that for you.

Re: remainder function
 

I do use it. But I don't want to be telling other people to use my custom function if there's already a perfectly good remainder function provided with FRC C++. I don't have access to a working C++ installation, otherwise I would test it myself. I am seeking help from knowledgeable C++ users on this forum.

Honestly, that's because I don't have a qualm. I am perfectly calm.

I have encounted at least one such scenario, and that's why I posted this thread.

For example, the IEC60559 remainder function can take any angle and normalize it to the range -180..+180 with a single C instruction:

normalizedAngle = remainder(angle,360);

I'd like to know if the remainder function is supported in FRC C++ so I can recommend it to students who are trying to do this type of conversion.

Neither the fmod() function nor the % operator can replicate the functionality of the remainder() function without using a bunch of conditional logic

If there are any Java programmers following this thread, Java appears to have the IEC 60559 remainder function; in Java it is called IEEERemainder. See attachments. If someone would be willing to test that (compare it to the implementation I posted ealier in this thread) I'd be grateful.



qualm
/kwä(l)m/
Noun

1) An uneasy feeling of doubt, worry, or fear; a misgiving.
2) A momentary faint or sick feeling.

Synonyms
nausea - queasiness

Re: remainder function
 

In a Java SE project this
yields this:
which I believe is what you are looking for.

However I cannot use IEEERemainder() in an FRC project they have compiled the jar without it apparently.

Re: remainder function
 

Excellent. Thank you! I'd give you some more reps, but it won't let me :(

Not being a Java user, I'm not sure what that means. Is there a way to re-compile to include it, or is that a major undertaking?


Are there any C++ gurus out there who can look into the same question for C++ ?

Re: remainder function
 

That's not entirely true. FRC uses the Squawk JVM, which is based on Java ME. Java ME does not require IEEERemainder(), which is why it isn't in java.lang.Math. However, Squawk does implement some features from Java SE, and puts them in other packages. In this case, IEEERemainder is in the com.sun.squawk.util.MathUtils package.

Re: remainder function
 

Thanks!
Is there a cross reference of where SE stuff that's been moved can be found?

Re: remainder function
 

Joe, you never cease to amaze me :)

Re: remainder function
 

Here's the result from the robot

Re: remainder function
 

It's all in the javadocs, but I'm not aware of an easy cross reference.

Re: remainder function
 

Bingo! They match.

Re: remainder function
 

From my installation, a grep through the headers folder shows no remainder functions. It's possible I'm missing something, but it looks like it doesn't exist at all in the vxWorks API.

As for the extern "C" option, yes that will make it compile, however the function will most likely not be resolved by the linker, which will cause problems when you try to run it. Wind River's system is designed to not complain about missing symbols until the cRIO's kernel tries to load the program. I'll check if this is the case tomorrow.

EDIT: actually, drem() does exist, and is defined to be the same as remainder() (see the glibc manual). However, the definition for it is in <private/trigP.h>, which isn't meant for inclusion by user programs. There don't seem to be any public headers which include it either.

Re: remainder function
 

Apparently in glibc, remainder() and drem() are two different names for the same function

Notice the very slight difference between the glibc and Java definitions (handling of divide-by-zero).

Re: remainder function
 

The "java" link you posted was to gnu libc...

Re: remainder function
 

Fixed. Take a look.

Re: remainder function
 

Joe, is the MathUtils.IEEEremainder() method available in 2015 FRC Java, now that the runtime engine has changed? If so, does it produce the exact same results?

Re: remainder function
 

It's in Math, rather then the squawk MathUtils workaround, but it still works.

Re: remainder function
 

Thanks Joe.

For those of you reading this thread for the first time, Math.IEEEremainder(angle,360.0) can be used to convert any angle (in degrees) to the range -180 to 180.

This can be very useful when working with the gyro.

Let's say you want to find the shortest angular error between your joystick direction angle and the gyro angle. This can be accomplished in one clean line of code as follows:

angle_error = Math.IEEEremainder(joystick-gyro,360.0);

There's no need for conditional logic. It cleanly handles all input angle ranges for joystick and gyro, including angles greater than 360 degrees and less than -360 degrees.

The above assumes that gyro and joystick share the same zero and measurement direction.