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long long int for floating average computation

I want to compute a floating average of third order.
Just take a look at my code:

void IRQ_Handler()__irq __ram
{
        static long long unsigned int ACC1,ACC2,ACC3,ACC3D;
        static long long unsigned int D1,D2,D3,D1D,D2D;
        static unsigned int int_counter;
        char text[10];

        T0CLRI = 0;
        ADCCON = 0x6A3;                 // software conv., single-ended, conv. enabled
        while (!ADCSTA){}               // wait for end of conversion

        ACC1 += (ADCDAT >> 16) * 100;
        ACC2 += ACC1;
        ACC3 += ACC2;

        if (!(int_counter++ & 0x7F))
        {
                D1 = ACC3 - ACC3D;
                D2 = D1 - D1D;
                D3 = D2 - D2D;
                ACC3D = ACC3;
                D1D = D1;
                D2D = D2;

                sprintf(text,"%8.d",D3 >> 21);
                SDA5708_printf(text);
        }
}

befor i used long long there were overflow.
If increasing Filter lenght there will be overflows even while using long long. Is there a work around?

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0 HansBernhard Broeker over 17 years ago

i used long long there were overflow.

With the algorithm as shown, there will always be overflow. It assumes infinitely large integers, which simply don't exist in any CPU. You keep adding non-negative numbers to ADC1 etc., but you never subtract anything. That leaves it no other way to go but through the roof.

You're also wasting a whole factor of 100 of usable range, for no apparent reason.

Ultimately, this is the wrong place to ask this. This is purely algorithmic question unrelated to both Keil and ARM.
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0 HansBernhard Broeker over 17 years ago

i used long long there were overflow.

With the algorithm as shown, there will always be overflow. It assumes infinitely large integers, which simply don't exist in any CPU. You keep adding non-negative numbers to ADC1 etc., but you never subtract anything. That leaves it no other way to go but through the roof.

You're also wasting a whole factor of 100 of usable range, for no apparent reason.

Ultimately, this is the wrong place to ask this. This is purely algorithmic question unrelated to both Keil and ARM.
Cancel
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