Logic not trapping

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August 30th, 2012, 10:38 AM

AstroTux

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Logic not trapping

Hi,

This code is short and sweet. It is complete as posted. The problem is this: when the value of hdg_ins exceeds M_PI*2.0 (360 degrees) or goes negative (less than 0) the bounds check fails and doesn't execute.

1) Why
2) How to fix it?

Code:

{
	hdg_error = hdg_error + ((7.0/25920000.0)*M_PI);
	if(hdg_error >= (M_PI*2.0)) hdg_error = hdg_error - (M_PI*2.0);
	if(hdg_error < 0.0) hdg_error = hdg_error + M_PI*2;

	inertial_hdg = inertial_hdg + (rateyaw * cos(-roll)) + (ratepitch * sin(-roll));
	hdg_ins = (inertial_hdg * 0.025) + hdg_error;

	if(hdg_ins >= (M_PI*2.0)) hdg_ins = hdg_ins - (M_PI*2.0);
	if(hdg_ins < 0.0) hdg_ins = hdg_ins + (M_PI*2.0);
}

Many thanks in advance.

Best regards,
AstroTux.

August 30th, 2012, 01:41 PM

salem

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I think you would need to post a test case we can copy/paste/run for ourselves.

Compiling a bit of code and stepping through with gdb shows nothing unexpected here.

Code:

Breakpoint 1, main () at foo.c:18
18	    if(hdg_ins >= (M_PI*2.0)) hdg_ins = hdg_ins - (M_PI*2.0);
(gdb) list
13	    if(hdg_error < 0.0) hdg_error = hdg_error + M_PI*2;
14	
15	    inertial_hdg = inertial_hdg + (rateyaw * cos(-roll)) + (ratepitch * sin(-roll));
16	    hdg_ins = (inertial_hdg * 0.025) + hdg_error;
17	
18	    if(hdg_ins >= (M_PI*2.0)) hdg_ins = hdg_ins - (M_PI*2.0);
19	    if(hdg_ins < 0.0) hdg_ins = hdg_ins + (M_PI*2.0);
20	    }
21	    
22	    return 0;
(gdb) set hdg_ins = 7
(gdb) step
19	    if(hdg_ins < 0.0) hdg_ins = hdg_ins + (M_PI*2.0);
(gdb) step
22	    return 0;
(gdb) print hdg_ins
$5 = 0.71681469282041377

(gdb) run
Breakpoint 1, main () at foo.c:18
18	    if(hdg_ins >= (M_PI*2.0)) hdg_ins = hdg_ins - (M_PI*2.0);
(gdb) set hdg_ins = -7
(gdb) step
19	    if(hdg_ins < 0.0) hdg_ins = hdg_ins + (M_PI*2.0);
(gdb) step
22	    return 0;
(gdb) print hdg_ins
$6 = -0.71681469282041377
(gdb)

I set positive and negative out of range values, and it all seems fine.

The only thing I can think of is if hdg_ins is a float, and you're getting some weird rounding very close to the range limits, which results in the adjustments still being out of range.

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August 30th, 2012, 02:15 PM

dwise1_aol

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It would also help if you gave us the test input values that you're using. Plus the variable declarations as salem alluded to.

August 30th, 2012, 03:03 PM

b49P23TIvg

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use fmod, not if if if

Code:

#define PI2 (2*M_PI)
{
  hdg_error += (7.0/25920000.0)*M_PI;
  hdg_error = fmod(hdg_error+PI2,PI2);
  inertial_hdg = inertial_hdg + (rateyaw * cos(-roll)) + (ratepitch * sin(-roll));
  hdg_ins = (inertial_hdg * 0.025) + hdg_error;
  hdg_ins = fmod(hdg_ins+PI2,PI2);
}

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September 7th, 2012, 10:01 AM

AstroTux

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Join Date: Feb 2008

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Hi,

It was the float vs. integer thing.

e.g.

Code:

double result = 1/6;

1/6 treated like an integer. Destination type is double. How can I change this default behavior?

If I have:

Code:

double result = 1.0/6.0;

I get the correct result.

Best regards,
AstroTux.

September 7th, 2012, 12:19 PM

EEmaestro

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Try this code & compare results.

Code:

     #include <stdio.h>

     int
     main (void)
     {
        double result;


        result = 1/6;
        printf ("\nresult = %f",result);

        result = 1./6.;
        printf ("\nresult = %f",result);

        result = (float) 1/6;
        printf ("\nresult = %f",result);

        result = (double) 1/6;
        printf ("\nresult = %f",result);

       return 0;
     }

Last edited by EEmaestro : September 7th, 2012 at 12:23 PM.

Logic not trapping

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