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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.lang.c
Subject: Re: Right shift vs. divide
Message-ID: <4734@alice.UUCP>
Date: Mon, 23-Dec-85 11:03:42 EST
Article-I.D.: alice.4734
Posted: Mon Dec 23 11:03:42 1985
Date-Received: Wed, 25-Dec-85 01:11:33 EST
References: <974@brl-tgr.ARPA>
Organization: Bell Labs, Murray Hill
Lines: 11

> Anyone still think they're the same thing?  This optimization only works
> if the numbers are known to be non-negative. A Pascal compiler may make
> this optimization, becausethe programmer may specify the range for
> variables, but not C.

Moral: a C compiler can substitute a right shift for a divide by
a constant power of two if and only if the LHS of the expression
is an unsigned integer type.

By the way, a right shift of a signed quanitity is not required to
be an arithmetic shift.