Raphi Houri wrote:
>
> ----------
> > From: Alan King <taking@intrex.net>
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: reversing bits
> > Date: Saturday, April 12, 1997 1:40 AM
> >
> > Tony Matthews wrote:
> > >
> > > Is there a simple (short) way to reverse the order of bits in a byte.
> > > or even better a nibble in the middle of a byte ?       Thanks
> >
> >
> >   Clear carry,
> >   Rotate left out of in byte (or right)
> >   Rotate right into out byte (or left)
> >   Repeat 8 times.  What went out of first byte goes into other side
> >    of second.  Actually, you don't have to clear the carry even..
> >
> > By the time you get done with it, the 16 inline instructions to rotl,
> >  rotr,rotl,rotr, & etc won't be much more than setting up a counter and
> > looping 8 times, and won't use ram or destroy anything..
> >
> > Alan
>
> Let's get back to basics
>
> exclusive OR truth table:
>
>         a   b   f(a,b)
>             -----------------
>         0   0 |   0
>         0  1  |   1
>         1  0  |   1
>         1  1  |   0
>
> >From the table, if you EOR a byte with all 1s you will get all the bytes
> inverted.
> You may also invert selected bits.
> example code:
>
>         (W=%11001001) EOR (%11111111) = %00110110
>
>         16c84 code:
>                 XORLW    0xff
>
> Boolean algebra is beautiful!

 Agreed but I wanted to reverse the order of bits not invert them and I
have gotten several good ideas thanks to all who replied. Tony M.
> Raphi Houri
> rhouri@pacbell.net