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From: kenner@lab.ultra.nyu.edu (Richard Kenner)
Subject: Re: aliased & packed?
Date: 1997/05/14
Message-ID: <5lc6cm$jh4$1@news.nyu.edu>#1/1
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References: <EA33z0.2ts@world.std.com> <1997May13.065907.1@eisner>
 <EA4nII.803@world.std.com>
Organization: New York University Ultracomputer Research Lab
Newsgroups: comp.lang.ada
Date: 1997-05-14T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <EA4nII.803@world.std.com> bobduff@world.std.com (Robert A Duff) writes:
>And it seems like more than a couple of instructions to shift and mask
>an 8-byte word (I mean, using 21064 instructions only), in the case
>where the byte you want is dynamic (i.e. you're indexing randomly into
>an array of bytes -- on the other hand, most array accesses are probably
>sequential).

The actual number of instructions depends on more than just if the byte
number (address mod 4) is known, but also on the form you have the address
in and on the value of the constant byte number, if known.

In most cases, byte loads are two instructions for both the static and
dynamic case.  For stores, it's between four and six instructions, with
the static case having four or five and the dynamic case six.