Re: [Devel] FT_SquareFix?

[Keith Packard]

Around 12 o'clock on Apr 28, Tom Kacvinsky wrote:

> I wonder: is there an optimization that could be made for calculating the
> square of two 16.16 fixed numbers?

Of course there is, if you're doing 16-bit partial products:

        a * a = (a0 * 65536 + a1) * (a0 * 65536 + a1)
              = a0*a0 * 2^32 + 2 * a1*a0 * 65536 + a1*a1

As you can see, you can eliminate a 16x16 multiply in the middle over
the usual multiplication routine.  This takes 3/4 the time of a simple 
multiply.

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