People have been designing clever bit-reversal algorithms since the 60s, (do
a net search for "hakmem and Schroeppel" for some nasty code that reverses 6
or 7 bits in 3 instructions, or 8 bits in 4 instructions (involves 36 bit
multiplications and divisions!))  I have a hard time believing that it's
ever important enough to build special purpose hardware within a processor
to do it.  I mean, the only time the actual order of the bits is relevant is
when doing math, and doing math and logical-bit operations on the same
numbers is pretty rare.  It's always easier to simply make your external
shift registers shift the other direction, or re-think the problem.  I think
I used a bit-reversal algorithm in a graphics hack once, but only because I
wanted the leftmost bits on the printer to match the leftmost bits in the
memory; and that was quite arbitrary; there's no reason that the MSB of a
word has to be thought of as being "on the left."

BillW

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