On Sep 13, 2005, at 6:48 PM, Mike Hord wrote:

>> I've heard about interesting trick shifting bits individually
>> into different positions by multiplying on constant on micros
>> with hardware multiplication unit.
>
> Pretty simple, actually.  A left shift (towards the MSB) is the
> same as a multiply by 2.  Each subsequent by 2 is a shift.
>
> So a shift by three bits to the left requires a multiply by...

Or did you mean something more complicated, like these bit reversal
algorithms from MIT's "hakmem" document:


;if A is 6 bit quantity, B gets 6 bits reversed (Schroeppel)
         IMUL A,[2020202]        ;4 copies shifted
         AND A,[104422010]       ;where bits coincide with reverse 
repeated base 2^8
         IDIVI A,377             ;casting out 2^8 - 1's

;reverse 7 bits (Schroeppel)
         IMUL A,[10004002001]    ;4 copies sep by 000's base 2 (may set 
arith. o'flow)
         AND A,[210210210010]    ;where bits coincide with reverse 
repeated base 2^8
         IDIVI A,377             ;casting out 377's

;reverse 8 bits (Schroeppel)
         MUL A,[100200401002]    ;5 copies in A and B
         AND B,[20420420020]     ;where bits coincide with reverse 
repeated base 2^10
         ANDI A,41               ;"
         DIVI A,1777             ;casting out 2^10 - 1's
>
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