A member wrote:

>better add some comments or a couple of weeks down the
road, you'll forget how clever you are :)

Thanks for the comment. Seems im not that clever at all. If i where, i would
probably have found a better way to make money than to deal with programming
of pics.

Its just, sometimes spending of additional brain can replace
spending of additional resources. In the end its only math.

; swapping vars without a third register:

    movf     Variable_1,w    ; w  = (v1 + v2) and 255
    xorwf    Variable_2,w
    xorwf    Variable_1,f      ; v1 = (v1 + v2) -v1 == v2
    xorwf    Variable_2,f      ; v2 = (v1 + v2) -v2 == v1


More swapping tricks,

; swapping vars, preserving contents of w and most status flags, no regs
used

    xorwf    Variable_1,w    ; w  = (w  + v1) and 255
    xorwf    Variable_2,w    ; w  = (w  + v2) and 255
    xorwf    Variable_1,f      ; v1 = (v1 + v2 + w) -v1 == v2 + w
    xorwf    Variable_2,f      ; v2 = (v1 + v2 + w) -v2 == v1 + w
    xorwf    Variable_1,w
    xorwf    Variable_2,w    ; w  = (w -v%_k^#\oops !??
    xorwf    Variable_1,f
    xorwf    Variable_2,f      ; dunno why this one happens :)


; swapping the contents of a register with w

    xorwf    Variable_1,w    ; w  = (w  + v1) and 255
    xorwf    Variable_1,F     ; v1 = (w  + v1) -v1 == w
    xorwf    Variable_1,W    ; w  = (w  + v1) - w == v1


Personally i feel when used right, XOR is one of the most powerful
instructions in assembler. In a sense it can compress 16 bits into 8. With
full reversability and without loss of any information.

Greetings Germain

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