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From: tim@amdcad.UUCP (Tim Olson)
Newsgroups: comp.sys.m68k
Subject: Re: Intel vs Motorola Byte ordering
Message-ID: <13957@amdcad.UUCP>
Date: Thu, 4-Dec-86 17:15:32 EST
Article-I.D.: amdcad.13957
Posted: Thu Dec  4 17:15:32 1986
Date-Received: Fri, 5-Dec-86 04:48:50 EST
References: <1509@ihlpl.UUCP> <1335@hoptoad.uucp> <138@pembina.alberta.UUCP> <791@nike.UUCP>
Reply-To: tim@amdcad.UUCP (Tim Olson)
Organization: Advanced Micro Devices, Sunnyvale, California
Lines: 34

In article <791@nike.UUCP> lamaster@pioneer.UUCP (Hugh LaMaster) writes:
>I, for one, would like to hear some good arguments for or against
>a particular byte ordering.  It is my belief that there is no
>intrinsic architectural reason for either one.  However, I am an
>unapologetic big-endian for two reasons:
>1)  A STANDARD is needed for the benefit of those of us who need
>to move BINARY data files between machines of different types,
>such as graphics and solids modeling data files;
>2)  Big Endian is easier to read for English speaking people
>because characters and floating point are in the same order as
>in English.  (Has anyone ever wondered why we don't write 1 Million
>as 000,000,1    ?)
>But are there any intrinsic reasons for a particular order?  Some
>people seem to think so.  What are they?

I think a major reason why many microprocessors are little-endian is that
they have an 8-bit ancestory, and to perform multi-precision arithmetic
efficiently, they must index from the least-significant byte to the
most significant.  However, this is less of a problem with larger word size
microprocessors, since multi-precision aritmetic is not used as much past
16 or 32 bits.

One benefit of big-endian byte ordering on large (32-bit or more) wordsize
machines is possible fast lexicographical comparison of character data with
the use of integer compare instructions.  Since the "direction" of MSB to
LSB (B = byte) is the same as MSb to LSb (b = bit) strings may be compared
a word at a time instead of byte-by-byte. (That is, as long as you use a
sane character encoding, not something like the CDC display-codes ;-)

	-- Tim Olson
	Advanced Micro Devices
	
"byte ordering preferences expressed in this article do not necessarily
represent the views of this station or its management"