0005942: llAngleBetween returns NaN for some rotations when 0.0 is the expected answer

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0005942

opensim

[REGION] Script Functions

public

2012-03-24 16:36

2012-07-28 21:33

Reporter

Kayaker Magic

Assigned To

Priority

normal

Severity

minor

Reproducibility

always

Status

new

Resolution

open

Platform

OS Version

Product Version

Target Version

Fixed in Version

Summary

0005942: llAngleBetween returns NaN for some rotations when 0.0 is the expected answer

Description

For some rotations, llAngleBetween returns NaN when I was expecting 0.0 because the two rotations were identical. It doesn't happen with all rotations, just sometimes. I captured this example rotation that repeats the problem by displaying the rotation returned from llGetRot() of a moving vehicle.

Steps To Reproduce

Create a prim, put the script below into it and save.
Note that the llAngleBetween returns NaN in this case while the two reference functions return the correct answer of 0.0
I attempted to diagnose the problem by comparing the results to the reference function from the LSL Wiki. I thought the problem could be fixed by checking for zeros and negatives, but this turned out to be unnecessary (the tAngleBetween function) because the simple reference function gets the correct answer without all the testing.

Additional Information

float sAngleBetween(rotation a, rotation b)
{
    return 2.0 * llAcos(
            (a.x * b.x + a.y * b.y + a.z * b.z + a.s * b.s)
          / llSqrt(
            (a.x * a.x + a.y * a.y + a.z * a.z + a.s * a.s)* (b.x * b.x + b.y * b.y + b.z * b.z + b.s * b.s)
                  )
                       );
}
float tAngleBetween(rotation a, rotation b)
{
    float n=(a.x * b.x + a.y * b.y + a.z * b.z + a.s * b.s);
    if (llFabs(n)<0.000001)
        return(0.0);
    float d=(a.x * a.x + a.y * a.y + a.z * a.z + a.s * a.s) * (b.x * b.x + b.y * b.y + b.z * b.z + b.s * b.s);
    if (d<0.000001) return(0.0);
    return 2.0 * llAcos(n / llSqrt(d));
}
default
{
    state_entry()
    {
        rotation ang1=<0.000000, 0.000000, -0.087156, 0.996195>;
        rotation ang2=<0.000000, 0.000000, -0.087156, 0.996195>;
        llOwnerSay("LSLib says: "+(string)llAngleBetween(ang1,ang2));
        llOwnerSay("simple says: "+(string)sAngleBetween(ang1,ang2));
        llOwnerSay("tested says: "+(string)tAngleBetween(ang1,ang2));
    }
}

Issue History
Date Modified	Username	Field	Change
2012-03-24 16:36	Kayaker Magic	New Issue
2012-07-28 21:33	SignpostMarv	Note Added: 0021929

Notes
(0021929) SignpostMarv (reporter) 2012-07-28 21:33	Cannot reproduce bug on master (using last night's version :P) Interestingly, the example script is broken in Second Life but works fine in OpenSim.

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