Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!umd5!brl-adm!brl-smoke!gwyn
From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: Shifting question
Message-ID: <8252@brl-smoke.ARPA>
Date: 29 Jul 88 02:22:34 GMT
References: <705@bnr-rsc.UUCP> <11556@steinmetz.ge.com> <60290@sun.uucp> <1818@spar.SPAR.SLB.COM> <11592@steinmetz.ge.com>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 14

In article <11592@steinmetz.ge.com> davidsen@crdos1.UUCP (bill davidsen) writes:
>| >	...If the value of the right operand is negative or is greater than or
>| >	equal to the width in bits of the promoted left operand, the behavior
>| >	is undefined.
>  So you have to build in an explicit check in every program, comparing
>the shift with the size of the item.

No; the vast majority of shifts in C applications do not require
the check.  However, if the language guaranteed the behavior you
want it to, then on many architectures a far larger percentage of
shifts would have to perform the check (in the compiler-generated
code).  This is one of the many cases where C is deliberately
permissive in order to allow a better fit to the hardware.  It is
of course not what an "ideal" programming language would do, where
"ideal" includes the notion of suitable hardware.