Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!lll-tis!ames!claris!apple!baum
From: baum@apple.UUCP (Allen J. Baum)
Newsgroups: comp.arch
Subject: Re: RISC is a nasty no-no!
Message-ID: <7482@apple.UUCP>
Date: 1 Mar 88 19:06:33 GMT
References: <179@wsccs.UUCP: <696@nuchat.UUCP: <284@scdpyr.UUCP> <25699@linus.UUCP> <11199@duke.cs.duke.edu> <25723@linus.UUCP> <8332@eddie.MIT.EDU>
Reply-To: baum@apple.UUCP (Allen Baum)
Organization: Apple Computer, Inc.
Lines: 11

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RE: needing multiplies in array accesses
Accessing arbitrary array elements is non extremely common. Most of the
array references are inside loops, and use the loop induction variables as
part of the subscript expression. A good compiler will strength reduce these
multiply operations and turn them into add/subtract immediates. Even if this
is not possible, the multiply operation is generally reg*imm, which reduces
to a shift in the common cases (power of two array sizes are pretty common!),
or a SMALL series of shifts and adds.

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