Path: utzoo!attcan!uunet!lll-winken!ames!amdcad!crackle!tim
From: tim@crackle.amd.com (Tim Olson)
Newsgroups: comp.arch
Subject: Re: Endian wars
Message-ID: <24238@amdcad.AMD.COM>
Date: 27 Jan 89 16:26:52 GMT
References: <6133@columbia.edu> <5124@aldebaran.UUCP>
Sender: news@amdcad.AMD.COM
Reply-To: tim@amd.com (Tim Olson)
Organization: Advanced Micro Devices, Inc. Sunnyvale CA
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In article <5124@aldebaran.UUCP> jimp@cognos.UUCP (Jim Patterson) writes:
| In article <6133@columbia.edu> eppstein@garfield (David Eppstein) writes:
| >Big endian lets you use integer comparison instructions to do string
| >compares a word at a time.  Little endian means you are stuck with a
| >byte at a time.
| 
| I'd like to see an algorithm that actually benefits from this.
| Consider...
| 
| If you don't know how long the string is (as for strcmp and strncmp),
| then you have to scan the string to find how long it is.  For a
| word-oriented algorithm to be effective here, you need an algorithm
| which detects which byte of a word (if any) contains a NUL.  
|
| If anyone has any good word-oriented implementations of memcmp or
| especially strcmp, I'd be interested in seeing them. 

A couple of years ago I posted essentially the string routines we use on
the Am29000.  These routines make use of:

	1)	comparisons a word at a time

	2)	the "cpbyte" instruction to detect a null byte in a word

	3)	the "extract" instruction (extract a 32-bit word from
		a 64-bit word pair at any bit boundary) to take care of
		misaligned operands

These routines broke even with a standard byte-at-a-time hand-coded
routine with 5-byte strings (including null) and were always better with
longer strings.


	-- Tim Olson
	Advanced Micro Devices
	(tim@crackle.amd.com)