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From: REICHETZ@AWIIMC12.BITNET (Christian Reichetzeder)
Newsgroups: comp.lang.asm370
Subject: Re: Why use an LA instruction?
Message-ID: <9103050050.AA15241@ucbvax.Berkeley.EDU>
Date: 5 Mar 91 00:50:09 GMT
References: <PGIFFORD@ALLEGVM>
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Reply-To: IBM 370 Assembly Programming Discussion List
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On Mon, 4 Mar 91 10:38:14 GMT Pete Gifford said:
>..starting with the instructions below. I understand all of it but the LA.
>Can someone shed some light on its purpose?
>PROGRAM  BALR  4,0                load base register
>         BCTR  4,0                back off one byte to point
>         BCTR  4,0                to label at start of program
>         LA    4,0(0,4)           ???????
Whoever wrote this had something in mind - there're rumors that there's been a
time when one of the major goals  in software writing was "just to confuse the
Russians".
Well, the  LA clears bits 0-7  (24bit mode) or  bit 0 (31bit mode)  to zeroes.
Still this  could be  done without  the BCTR instruction  (given that  you are
happy with the base register offset 2 bytes from the entry point).
Christian