[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Devel] FT_SquareFix?
From: |
Keith Packard |
Subject: |
Re: [Devel] FT_SquareFix? |
Date: |
Sat, 28 Apr 2001 16:18:56 -0700 |
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.
address@hidden XFree86 Core Team SuSE, Inc.