remainder function

[nightpool]

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

[Ether]

Originally Posted by nightpool

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

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

[sur]

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

#include <cmath>
using namespace std;

extern "C" double remainder(double, double);

[Ether]

Originally Posted by sur

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

#include <cmath>
using namespace std;

extern "C" double remainder(double, double);

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

double myRemainder(double x, double y){
return x-y*floor(0.5+x/y);
}

[Racer26]

What about:

double EthersRemainder( double x, double y ){

int wholenumber;

wholenumber = (int)(x/y);

double result;

result = (x - (wholenumber * y));
if(result > 0.5*y) {
result -= y;
}

return result;

}

[Ether]

Originally Posted by 1075guy

What about:
EthersRemainder

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:

double myRemainder(double x, double y){
  return x-y*floor(0.5+x/y);
}

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

[Racer26]

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.

[Ether]

Originally Posted by 1075guy

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

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.

I don't understand your qualm?

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

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.

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

[omalleyj]

In a Java SE project this

        double result;
        double x[] = {179, 180, 181, 359, 721, -1, -179, -180, -359, -361, -721};

        for (int i = 0; i < x.length; i++){
            result = Math.IEEEremainder(x[i],360.0); 
            System.out.println("x: " + x[i] + " rem y: 360 result: " + result);
        }

yields this:

x: 179.0 rem y: 360 result: 179.0
x: 180.0 rem y: 360 result: 180.0
x: 181.0 rem y: 360 result: -179.0
x: 359.0 rem y: 360 result: -1.0
x: 721.0 rem y: 360 result: 1.0
x: -1.0 rem y: 360 result: -1.0
x: -179.0 rem y: 360 result: -179.0
x: -180.0 rem y: 360 result: -180.0
x: -359.0 rem y: 360 result: 1.0
x: -361.0 rem y: 360 result: -1.0
x: -721.0 rem y: 360 result: -1.0

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.

[Ether]

Originally Posted by omalleyj

In a Java SE project this

[snip]

yields this:

[snip]

which I believe is what you are looking for.

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

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

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++ ?

[Joe Ross]

Originally Posted by omalleyj

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

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.

[omalleyj]

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

[Joe Ross]

Originally Posted by omalleyj

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

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

[Ether]

Originally Posted by Joe Ross

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.

Joe, you never cease to amaze me

[Joe Ross]

Here's the result from the robot

        double result;
        double x[] = {179, 180, 181, 359, 721, -1, -179, -180, -359, -361, -721};

        for (int i = 0; i < x.length; i++){
            result = MathUtils.IEEEremainder(x[i],360.0); 
            System.out.println("x: " + x[i] + " rem y: 360 result: " + result);
        }

[cRIO] x: 179.0 rem y: 360 result: 179.0
[cRIO] x: 180.0 rem y: 360 result: 180.0
[cRIO] x: 181.0 rem y: 360 result: -179.0
[cRIO] x: 359.0 rem y: 360 result: -1.0
[cRIO] x: 721.0 rem y: 360 result: 1.0
[cRIO] x: -1.0 rem y: 360 result: -1.0
[cRIO] x: -179.0 rem y: 360 result: -179.0
[cRIO] x: -180.0 rem y: 360 result: -180.0
[cRIO] x: -359.0 rem y: 360 result: 1.0
[cRIO] x: -361.0 rem y: 360 result: -1.0
[cRIO] x: -721.0 rem y: 360 result: -1.0