Path: utzoo!attcan!uunet!pcrat!rick
From: rick@pcrat.UUCP (Rick Richardson)
Newsgroups: comp.arch
Subject: Re: Shifting question
Message-ID: <529@pcrat.UUCP>
Date: 19 Jul 88 11:41:37 GMT
References: <705@bnr-rsc.UUCP> <392@attila.weitek.UUCP>
Reply-To: rick@pcrat.UUCP (Rick Richardson)
Organization: PC Research, Inc., Tinton Falls, NJ
Lines: 21

In article <392@attila.weitek.UUCP> mahar@attila.UUCP (Mike Mahar) writes:
>The question (x>>32) has come up.  K&R and ANSI-C say the result is undefined.
>The 68000 shift instruction will give you a 0.
>The 80286 shift instruction will give you a 0.

This depends upon your 80286 compiler, whether x is an int or a long, and
whether you try shift 16 or 32 bits.  The AT&T 80286 compiler (GET THIS!)
actually detects:
		some_long >> 32
		some_int >> 32
and explicity generates code to give the result as "some_long" or "some_int"!
At first, I thought this implementation choice was for consistency with the
case where the shift count is a variable.  But alas, if x is "32":
		some_long >> x		gives result "0"
		some_int >> x		gives result "some_int"
So this compiler isn't even consistent in its treatment of this problem.
-- 
		Rick Richardson, PC Research, Inc.

(201) 542-3734 (voice, nights)   OR     (201) 389-8963 (voice, days)
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