Xref: utzoo comp.sys.ibm.pc:23354 comp.sys.intel:672
Path: utzoo!attcan!uunet!lll-winken!ames!amdahl!drivax!alexande
From: alexande@drivax.DRI (Mark Alexander)
Newsgroups: comp.sys.ibm.pc,comp.sys.intel
Subject: Re: correct code for pointer subtraction
Summary: use 'rcr' not 'shr'
Message-ID: <4150@drivax.DRI>
Date: 17 Jan 89 03:36:27 GMT
References: <597@mks.UUCP> <3845@pt.cs.cmu.edu> <18123@santra.UUCP> <142@bms-at.UUCP> <6604@killer.DALLAS.TX.US> <4121@drivax.UUCP>
Reply-To: alexande@drivax.UUCP (Mark Alexander)
Organization: Bob-ist Temple of Monterey
Lines: 12

In article <4121@drivax.UUCP> I wrote without thinking very hard:
:	mov	BX,offset DGROUP:U0EA60h	; &a[30000]
:	mov	SI,offset DGROUP:U0		; &a[0]
:	sub	BX,SI				; &a[30000] - &a[0]
:	sar	BX,1				; convert bytes to words
:That last 'sar' instruction should really be a 'shr'.

Actually, it should be 'rcr', to handle the case where the first pointer
is less than the second.  Thanks to Larry Jones (uunet!sdrc!scjones)
for pointing this out to me.  That darned carry flag always confuses me.
-- 
Mark Alexander	(amdahl!drivax!alexande) (no 'r')