Paul Haas <paulh@hamjudo.com> wrote:

> I'm sure someone on the list has a clever way of converting a number
> in the range 0 to 7 into a bitmask with one bit set and vice versa.

Paul:

Here's the most obscure way I could come up with to convert from a
number in the range [0-7] to a bitmask.

9 words of program space and between 3 and 10 cycles to execute.

Note that this routine is subject to the usual "direct modification
of the Program Counter" limitations (e.g., on a 16C5x, the whole
thing must be in the first half of a page; and on the other parts,
PCLATH must be set apropriately before the "ADDWF" is executed).

    ADDWF   PCL             ;CALCULATE 2^W, WHERE W IS IN THE
    ADDLW   0               ;RANGE [0-7].
    ADDLW   -1              ;
    ADDLW   -3              ;
    ADDLW   -7              ;
    ADDLW   -15             ;
    ADDLW   -31             ;
    ADDLW   -63             ;
    ADDLW   121             ;

-Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499