Personally I don't know of any computer ever constructed in the history
of computing that have an instruction that reverses the bits within a
byte/word like what you want. Also I don't know of any programming
language in the history of computing that has built in functions to do
what you want. So you'll have to do it yourself regardless of what
programming language or CPU you use.
Machines with special features to help with Fourier
transforms (digital signal processors and the like) have,
I'm told, addressing modes where array indices are bit-
reversed. Thus, a loop that runs from "0 to 7" would
access elements 0, 4, 2, 6, 1, 5, 3, and 7, in that order.
I don't know whether such machines can deliver the bit-
reversed index as an explicit value, or whether the reversal
remains hidden within the addressing circuitry. Nor do I
know how the capability is usually exposed to programmers.
Nonetheless, the bit-reversal action is certainly present.
The only circumstance I've seen where bit-reversal is
called for is when you're rearranging the transformed values
after the Fast Fourier Transform's "butterfly" steps have
scrambled them (or pre-scrambling the inputs beforehand,
depending on how the FFT is set up). So when someone asks
about bit-reversal I immediately suspect he's doing FFT's --
and if he's doing FFT's, there's at least a chance he's
doing them on a machine with special capabilities, and those
capabilities may even be exposed to C. Not as an integral
part of the language, of course, but as an extension or a
set of extra functions or something of the kind. If it's
there, the O.P. will need to search the documentation for it.
