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From: nickroberts@blueyonder.co.uk (Nick Roberts)
Newsgroups: comp.lang.ada
Subject: Re: Calculate and set Parity
Date: Wed, 18 Sep 2002 20:25:53 GMT
Organization: AdaOS
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Date: 2002-09-18T20:25:53+00:00
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On Wed, 18 Sep 2002 00:17:15 GMT, tmoran@acm.org strongly typed:

>The XOR of the parities equals the parity of the XORed bytes.
>Thus the code can be shortened:
>...

Absolutely correct. I forgot this in my haste (and the lateness of the
hour). The revised code then is:

   MOV AX, Data    ; load a 16-bit word
   XOR AL, AH      ; XOR upper byte with lower
                   ; and at the same time set PF
   LAHF            ; load flags byte
   SHR AH, 2       ; shift PF into bit 0
   AND AH, 1       ; mask off all other bits

which leaves the result in AH. 

-- 
Nick Roberts
Per Ardua ad Disastra