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Strange behaviour while comparing pad coordinates from ULP

atelszewski

Hi,

 

In a package I create SMD pad with the following coordinates [mm]: x = -2.54, y = 2.8.

 

When I run the following ULP, the message displayed is "not OK", while it should be "OK":

package( P )
{
    P.contacts( C )
    {
        real y = u2mm( C.y );
       
        if( y ==  2.8 )
        {
            dlgMessageBox( "OK" );
        }
        else
        {
            dlgMessageBox( "not OK" );
        }
       
        break;
    }
}

 

Now, if I change the ULP to be as follows, the result is "OK":

package( P )
{
    P.contacts( C )
    {
        real y = u2mm( C.y );
        real d = u2mm( 28000 );
        if( y ==  d )
        {
            dlgMessageBox( "OK" );
        }
        else
        {
            dlgMessageBox( "not OK" );
        }
       
        break;
    }
}

 

Now I change the pad coordinates to [mm]: x = 2.46, y = 1.8 and run the following ULP and the result is "OK":

package( P )
{
    P.contacts( C )
    {
        real y = u2mm( C.y );
       
        if( y ==  1.8 )
        {
            dlgMessageBox( "OK" );
        }
        else
        {
            dlgMessageBox( "not OK" );
        }
       
        break;
    }
}

 

 

The question is, where is the problem? Is there a bug or am I doing something wrong?

 

Best regards,

Andrzej Telszewski

  • 0

    Andrzej Telszewski <communitymanager@premierfarnell.com> wrote:

    Hi,

     

    In a package I create SMD pad with the following coordinates : x = -2.54, y = 2.8.

     

    When I run the following ULP, the message displayed is "not OK", while it should be "OK":

    package( P )

    {

        P.contacts( C )

        {

            real y = u2mm( C.y );

           

            if( y ==  2.8 )

            {

                dlgMessageBox( "OK" );

            }

            else

            {

                dlgMessageBox( "not OK" );

            }

           

            break;

        }

    }

     

    Now, if I change the ULP to be as follows, the result is "OK":

    package( P )

    {

        P.contacts( C )

        {

            real y = u2mm( C.y );

            real d = u2mm( 28000 );

            if( y ==  d )

            {

                dlgMessageBox( "OK" );

            }

            else

            {

                dlgMessageBox( "not OK" );

            }

           

            break;

        }

    }

     

    Now I change the pad coordinates to : x = 2.46, y = 1.8 and run the

    following ULP and the result is "OK":

    package( P )

    {

        P.contacts( C )

        {

            real y = u2mm( C.y );

           

            if( y ==  1.8 )

            {

                dlgMessageBox( "OK" );

            }

            else

            {

                dlgMessageBox( "not OK" );

            }

           

            break;

        }

    }

     

     

    The question is, where is the problem? Is there a bug or am I doing something wrong?

     

    Be careful with floats. Alot of apparently precise values are not. Even

    numbers with one digit may be a result of rounding. It is better to work in

    int (u) space.

     

    Try multiplying your 2.8 with 1e9 and you may be surprised with the result.

    You could also try printing it with a lot of decimals.

     

  • 0 in reply to Former Member

    Hi,

     

    You are right, the problem lies in rounding error.

    But I just didn't suppose it can come out in such a simple calculations.

     

    Thanks.

     

    Best regards,

    Andrzej Telszewski