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Re: [avr-gcc-list] update on the last issue

From: E. Weddington
Subject: Re: [avr-gcc-list] update on the last issue
Date: Tue, 05 Apr 2005 10:54:44 -0600
User-agent: Mozilla Thunderbird 0.7.3 (Windows/20040803)

intiha Ho gai wrote:

Thank you. Okay.. i can live with that.. for now.. but my issue is.. will the
long long addition be correct?
Also if it is, then why isnt the solution for the equation to
calculate a (slope) and b(offset) coming out incorrect. For the above
code where I hand coded the values of all long longs
  table.sumX = 12338578LL;
      table.sumY = -3336078LL;
table.sumXSquared = 7260107358192LL; table.sumXY = -1646741910392LL; denom = ( table.n * table.sumXSquared - table.sumX * table.sumX);
       if (denom != 0)
              a = (double)( table.n * table.sumXY - table.sumY *
table.sumX) / denom;
       b = (double)(table.sumY - a * table.sumX) / table.n;

    sprintf(OutputMsg,"**************** A=%f     B=%f ***********\r\n",a,b);
    UARTOutput(DBG_ERROR,"%s", &OutputMsg);

I get on the UART

**************** A=-0.045255     B=-106838.632813 ***********

While the actual values of a and b that i have precomputed should be a
= -0.000208 , and b = -133340.419011
What is the value of table.n that you are using in the code above to get the results that you gave?

Is table.sumXSquared supposed to be the square of table.sumX?

Please give us more information about what you are doing here.

Also, could you post/attach the assembly output of the above code snippet?


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