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Altera_Forum's avatar
Altera_Forum
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16 years ago

C2H fixed point mpy

I had an array of fixed point numbers, log values actually. 10 bit integer 22 bit fraction. Needed the sum of squares to calculate standard deviation. In regular C this works okay ... lo...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

Try this:

Square = (long long)val * (long long)val;

SumSquare += Square >> 22;

By the looks of it the CPLI of your loop is 1 before and after this change so your performance shouldn't differ.

Can you open a mysupport service request and attach your design so that this can be tracked and resolved. The result of your multiplication should have been a long long and the upper bits shifted down like you intended.