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From: knudsen@ihwpt.UUCP (mike knudsen)
Newsgroups: comp.sys.m68k
Subject: Re: Byte ordering, and pros/cons
Message-ID: <1271@ihwpt.UUCP>
Date: Wed, 26-Nov-86 18:19:54 EST
Article-I.D.: ihwpt.1271
Posted: Wed Nov 26 18:19:54 1986
Date-Received: Thu, 27-Nov-86 01:59:31 EST
Distribution: net
Organization: AT&T Bell Labs, Naperville, IL
Lines: 24

The rationale for Intel and 6502 byte ordering is that it
is natural and consistent for *arithmetic* operations,
including the adds and subtracts in address calculations.
That is, higher addresses have higher-significance bytes.

Motorola's ordering makes for slower arithmetic, since
you have to go back and fix the carries afterwards.
However, it is easier to read values in a Hex dump.

More important, tho less generally known, Motorola
byte ordering is better for *graphics* bit-blitting,
since the bytes have the same left-to-right ordering
in the registers as they do in memory.
Graphics programs on Intel procs have to swab bytes
to undo the automatic swab done by the chip
on stores and fetches.

Could this be why most graphics-oriented machines
use 68K chips??	--mike k
-- 
Mike J Knudsen    ...ihnp4!ihwpt!knudsen
Bell Labs (AT&T)   (312)-979-4132 (work)
You think AT&T cares about CoCos, music, or Star Trek?
No?  Then, these opinions must be all mine!