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From: ken@turtlevax.UUCP (Ken Turkowski)
Newsgroups: net.arch
Subject: Re: Right shift vs. divide
Message-ID: <1019@turtlevax.UUCP>
Date: Fri, 10-Jan-86 17:39:52 EST
Article-I.D.: turtleva.1019
Posted: Fri Jan 10 17:39:52 1986
Date-Received: Mon, 13-Jan-86 08:03:11 EST
References: <3000002@convexs> <4782@alice.UUCP>
Reply-To: ken@turtlevax.UUCP (Ken Turkowski)
Organization: CIMLINC, Inc. @ Menlo Park, CA
Lines: 24

In article <4782@alice.UUCP> ark@alice.UucP (Andrew Koenig) writes:
>	-2147483648 is 80000000 hex.  Negate it and you
>	get integer overflow.  If this is masked, most machines
>	will give you 80000000 hex back.
>
>	Shift 80000000 right 1 bit, giving C0000000.
>
>	Negate this again, giving 40000000.
>
>Thus, the sign gets lost.

Wrongo.  After you negate the original negative number, it becomes an
unsigned number without overflow.  When you shift, you use an unsigned
shift.  Then,

	Shift 80000000 right by 1 bit, giving 40000000.

	Negate this again, giving, C0000000 (-1073741824)

This is the correct result.
-- 
Ken Turkowski @ CIMLINC, Menlo Park, CA
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