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From: gah@hood.hood.caltech.edu (Glen Herrmannsfeldt)
Newsgroups: comp.lang.asm370
Subject: Re: Why use an LA instruction?
Message-ID: <gah.668685945@valine>
Date: 11 Mar 91 10:05:45 GMT
References: <9103050049.AA15223@ucbvax.Berkeley.EDU>
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PGIFFORD@ALLEGVM.BITNET (Pete Gifford) writes:

>I was disassembling a program (not copyrighted!) a while ago and found it
>starting with the instructions below.  I understand all of it but the LA.
>Can someone shed some light on its purpose?
>- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>Pete Gifford           PGIFFORD@ALLEGVM
>Systems Manager        PETE@MUSIC.ALLEG.EDU
>Allegheny College      (814) 332-5304
>Meadville, PA          (814) 332-5366


>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)           ???????

Well, I believe it throws away the 8 high order bits.

At least it used to, I don't know about in XA.