Its all at
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under routines, math, bit operations, reversing bit order in a byte

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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Scott Dattalo
Sent: Sunday, March 19, 2000 06:14
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Reversing the order of bits in a register.


On Sun, 19 Mar 2000, Nikolai Golovchenko wrote:

>         cblock
>         In
>         Out
>         endc
>
> #define A_MASK 1
> #define B_MASK 2
> #define C_MASK 4
> #define D_MASK 8
> #define E_MASK 16
> #define F_MASK 32
> #define G_MASK 64
> #define H_MASK 128
>
>         clrw
>         btfsc In, 7
>         iorlw A_MASK
>         btfsc In, 6
>         iorlw B_MASK
>         btfsc In, 5
>         iorlw C_MASK
>         btfsc In, 4
>         iorlw D_MASK
>         btfsc In, 3
>         iorlw E_MASK
>         btfsc In, 2
>         iorlw F_MASK
>         btfsc In, 1
>         iorlw G_MASK
>         btfsc In, 0
>         iorlw H_MASK
>         movwf Out

For a single byte there is a 14-cycle solution. But since it looks like your
having fun, I wouldn't want to spoil anything. :)

BTW, John Payson posted the original solution (for reversing 7 bits). Dmitry
optimized it slightly (again for 7 bits). John's trick is applicable here as
well.

Hint, for the general case, it takes 4 cycles to swap 2 bits. However, it
only
takes 2 cycles for the first two bits.

Scott