Denny's previous post is essentially defines it:

// Defining the table:
unsigned char TableA[] =3D {0x82,0x04,0x40,0x80};
unsigned char mask =3D 0x33; // mask out bits 7,6,3, and 2

// Using the table:
shadowA =3D PORTA & mask; // Get PORTA masking out output bits.
inputA =3D shadowA & 0x03; // input is PORTA bits 1,0
shadowA =3D shadowA | TableA[inputA]; // Get output from table and merge wi=
th shadow
PORTA =3D shadowA; // Write the output from shadow back to PORTA

Of course C can be obfuscated into a single statement:
PORTA =3D shadowA | TableA[(shadowA =3D PORTA & mask) & 0x03];

Interesting what you can do when assignment is an expression and not a
statement.

BAJ


On Mon, Sep 14, 2015 at 04:19:40PM -0500, Richard R. Pope wrote:
> Byron,
>      Could you please translate this into C for me?
> Thanks,
> rich!
>=20
> On 9/14/2015 11:14 AM, Byron Jeff wrote:
> > Richard,
> >
> > Your description below screams table. Since it's only 2 bits, the table
> > would be 4 entries long:
> >
> > TableA: ; W is input. Returns table entry in W.
> > 	andlw	0x3	; make sure only 2 lowest bits are used
> > 	addwf	PC,F	; jump to appropriate table entry
> > 	retlw	0x82	; return 1001 in bits 7-6,3-2 if input is 00
> > 	retlw	0x04	; return 0010 in bits 7-6,3=3D2 if input is 01
> > 	retlw	0x40	; return 0100 in bits 7-6,3=3D2 if input is 10
> > 	retlw	0x80	; return 1000 in bits 7-6,3=3D2 if input is 11
> >
> > Make a similar table for B.
> >
> > Then all you'd need to do is read the port, clear the output bits, call=
 the
> > table routine, OR back in the results, and write the whole mess back to=
 the
> > port.
> >
> > Hope this helps,
> >
> > BAJ
> >
> > On Mon, Sep 14, 2015 at 10:31:15AM -0500, Richard R. Pope wrote:
> >> Jan-Erik,
> >>       I guess my next question is about packing the register. The RA0-=
1
> >> and RB0-1 bits are my inputs. On Port A the output pins are 2-3 and 6-=
7.
> >> On Port B it is 2-5. So if I have two output registers. One called
> >> OutputA and the other OutputB. When the input is 0-0 then the output i=
s
> >> 1-0-0-1. If the input is 0-1 then the output is 0-0-1-0. If it is 1-0
> >> the output is 0-1-0-0 and if it is 1-1 the the output is 1-0-0-0. I
> >> guess we should define some constants called Bit# such as Bit0, Bit1,
> >> Bit2 and so forth to Bit7. These should be set to 1, 2, 4, 8, and so
> >> forth up to 128. We first have to clear the registers to zero with
> >> OutputA or B =3D 0; So do we add RA, B 0 and 1 together? And here is w=
here
> >> I get lost.  I just don't understand how to turn RA and B 0 and 1 in t=
o
> >> the proper number to put into the output bits. Would you please help m=
e
> >> with this.
> >> Thanks,
> >> rich!
> >>
> >> P.S. This is how it should look.
> >> --------------------------------- ----------------------------------
> >>                   |    Input    |    Output                  |
> >>             |    Input    |    Output |
> >>                   |   Bits       |    Bits    PortA          |
> >>            |    Bits      |    Bits   PortB |
> >>                   |-----|-----|-----|-----|-----|-----|
> >> |-----|-----|-----|-----|-----|------|
> >>                   |   1  |   0   |   2   |   3  |   6   |   7  |
> >>                |   1   |   0  |   2   |   3  |   4   |   5    |
> >>                   |-----|-----|-----|-----|-----|-----|
> >> |-----|-----|-----|-----|-----|------|
> >>                   |   0   |   0  |  1   |   0   |   0   |   1  |
> >>                   |   0  |    0  |   1   |   0  |    0  | 1    |
> >>                   |-----|-----|-----|-----|-----|-----|
> >> |-----|-----|-----|-----|------|-----|
> >>                   |   0   |  1   |  0   |   1   |   0   |   0 |
> >>                   |   0  |    1  |   0  |   1   |    0 |   0   |
> >>                   |-----|-----|-----|-----|-----|-----|
> >> |-----|-----|-----|-----|------|-----|
> >>                   |   1   |   0  |   0  |   0   |   1   |   0  |
> >>                |   1   |   0  |   0  |   0   |   1    | 0   |
> >>                   |-----|-----|-----|-----|-----|-----|
> >> |-----|-----|-----|-----|------|-----|
> >>                   |   1  |   1   |   0   |   0  |   0   |   1 |
> >>                   |   1  |    1  |   0   |   0  |    0 |   1   |
> >>                   |-----|-----|-----|-----|-----|-----|
> >> |-----|-----|-----|-----|------|-----|
> >> Thanks,
> >> rich!
> >>
> >>
> >> On 9/13/2015 6:00 AM, Jan-Erik S=F6derholm wrote:
> >>
> >> --=20
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--=20
Byron A. Jeff
Associate Professor: Department of Computer Science and Information Technol=
ogy
College of Information and Mathematical Sciences
Clayton State University
http://faculty.clayton.edu/bjeff
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