AVR-Chat

On Wednesday 08 June 2005 08:37, Dave VanHorn wrote:
> At 07:15 PM 6/7/2005, Dave Hylands wrote:
> > > I'm pretty sure this table is right.

> >And what I often do is write a little C program which I compile on my
> >PC that I use to generate source code for tables like this (or CRC
> >lookups etc).
> >
> >I typically include the C program #if 0'd out in my source file that
> >uses it as a way of documenting how the table was actually created.
>
> A good idea!
>
> >If you don't want to use 256 bytes for the lookup table, you could
> >also do a pair of (or a single) 16 byte lookup table which flipped 4
> >bits. Now you have a pretty wide execution time/space tradeoff and you
> >can picks what's appropriate for your project.

> I don't really need it, I was just musing about it.
> We have rotate and swap instructions, but not "flip" (or whatever
> you'd call it.)


You do... but despite my being able to rake in the millions by
patenting the bleeding obvious in the USA, it's called an
exclusive-or with a 1 for all bits you want to flip. :-)

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