Chief Delphi - remainder function

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Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- C/C++ (http://www.chiefdelphi.com/forums/forumdisplay.php?f=183)

- - remainder function (http://www.chiefdelphi.com/forums/showthread.php?t=112483)

Ether

01-02-2013 14:12

Re: remainder function

Quote:

Originally Posted by 1075guy (Post 1225912)

OK, so do this instead:

Code:

output = (719 % 360 > 180) ? (-360 + (719 % 360)) : (719 % 360);

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

Ether

01-02-2013 14:16

Re: remainder function

Quote:

Originally Posted by sur (Post 1225857)

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

Code:

#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:

Code:

double myRemainder(double x, double y){

return x-y*floor(0.5+x/y);

}

Racer26

01-02-2013 15:12

Re: remainder function

What about:

Code:

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

01-02-2013 15:41

Re: remainder function

Quote:

Originally Posted by 1075guy (Post 1225996)

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:

Code:

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

01-02-2013 17:23

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.

Ether

01-02-2013 18:16

Re: remainder function

2 Attachment(s)

Quote:

Originally Posted by 1075guy (Post 1226058)

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.

Quote:

I don't understand your qualm?

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

Quote:

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

01-02-2013 19:06

Re: remainder function

In a Java SE project this

Code:

        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:

Code:

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

01-02-2013 20:23

Re: remainder function

Quote:

Originally Posted by omalleyj (Post 1226113)

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 :(

Quote:

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

01-02-2013 20:34

Re: remainder function

Quote:

Originally Posted by omalleyj (Post 1226113)

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

01-02-2013 20:39

Re: remainder function

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

Ether

01-02-2013 20:49

Re: remainder function

Quote:

Originally Posted by Joe Ross (Post 1226149)

Joe, you never cease to amaze me :)

Joe Ross

01-02-2013 21:54

Re: remainder function

Here's the result from the robot

Code:

        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);

        }

Quote:

[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

Joe Ross

01-02-2013 21:55

Re: remainder function

Quote:

Originally Posted by omalleyj (Post 1226152)

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

01-02-2013 22:17

Re: remainder function

Quote:

Originally Posted by Joe Ross (Post 1226192)

Here's the result from the robot

Bingo! They match.

Radical Pi

02-02-2013 02:16

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.

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