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Altera_Forum
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14 years ago

Fixed Point Rounding

Hey guys,

I have one more question about fixed point rounding. If you multiply two numbers and have to perform rounding, how would you do that with fixed point? I'm currently rounding a 32 bit product down to 16 bits by truncating the first 15 bits, thus performing a division by 2^15. But, if you have four bits representing the fractional part, how do you perform the rounding?

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  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    There are few rounding algorithms:

    direct truncation (same as floor of matlab)

    basic (same as nearest of matlab)

    dc unbiassed (convergent of matlab)

    round to nearest integer (round of matlab)

    I normally go for basic: very simple:

    to round 32 bits to 16 bits: add msb of truncated section (bit index 15)

    to the 16 bits(b31:b16). thats all but be careful about saturation.