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In article: <4fn5qu$ejm@nyheter.chalmers.se>  Bengt-Inge Dalenback <bid@ta.chalmers.se> writes:
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> From: Bengt-Inge Dalenback <bid@ta.chalmers.se>
> Newsgroups: comp.lang.modula2
> Subject: Re: XOR function
> Date: 12 Feb 1996 10:46:54 GMT
> Organization: CATT & Dep. of Applied Acoustics, Chalmers
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> References: <1996Feb8.114044.15072@ucl.ac.uk>
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> X-XXDate: Mon, 12 Feb 1996 10:48:46 GMT
> 
> In article <1996Feb8.114044.15072@ucl.ac.uk> Chris Austin,
> zcaccau@cs.ucl.ac.uk writes:
> >Is there an XOR function in Topspeed Modula-2 V3.something.  I want to be
> >able to XOR either 2 cardinals or 2 BITSETs, so if there isn't a function,
> >what is the best way to implement it.  I need speed, not simplicity, as this
> >is for graphics routines.
> >
> 
> I just yesterday needed that to create a XOR checksum required for the
> Windows "placeable" Meta-file header!
> 
> Low-level tricks like that can be done using SET operations. XOR is "/"
> which means for A, B and C CARDINALs:
> 
>   "C = A XOR B" <=> C := CARDINAL( BITSET(A) / BITSET(B) );
> 
> Check out the "TopSpeed Language Tutorial" on SETs in case I remembered
> it wrong. TopSpeed also has a "bitwise boolean operator" pragma that
> sometimes
> can be handy but which of course is nonportable.
> 

It may also me much quicker to use the assembly language routine. 
You could use the Visual Debuger to view the asam code and see
which is the quickest. XOR as a machine instrction between to 
16 bit registers is about 2 clock cycles.

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