Re: [MI400] Reverse of XOR.

["James H. H. Lampert" <jamesl@xxxxxxxxxxx>]

Harry Williams wrote:
>
> I want to find the reverse of an XOR statement.
>
> Example  of xor
> XXXX   XOR  YYYY  = ZZZZ
>
> Now if I have  ZZZZ and YYYY how do I find XXXX?

XORing ZZZZ and YYYY should get you back to XXXX.

Consider:
    0 XOR 0 = 0
    0 XOR 1 = 1
    1 XOR 0 = 1
    1 XOR 1 = 0
and if you switch the operators in the above assertions, they all remain valid.

This, by the way, is why XOR operations are often used for graphics that
have to be rapidly superimposed over other graphics (e.g., "rubber band"
selection), without the use of an additional raster as a "sprite plane."
Such graphics can be rapidly drawn and erased simply by drawing them in
XOR mode, then redrawing in XOR mode to erase.

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James H. H. Lampert
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