Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!rochester!rit!ultb!jed4885
From: jed4885@ultb.UUCP (J.E. Dyer)
Newsgroups: comp.arch
Subject: Re: Understanding variations in Dhrystone performance
Summary: Search word for byte instruction?
Message-ID: <839@ultb.UUCP>
Date: 18 May 89 13:55:37 GMT
References: <474@estevax.UUCP> <1989May15.173631.3029@utzoo.uucp> <1989May16.172354.1417@utzoo.uucp>
Reply-To: jed4885@ultb.UUCP (J.E. Dyer (713ICS))
Organization: Rochester Institute of Technology, Information Systems
Lines: 27

In article <1989May16.172354.1417@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>In article <1989May15.173631.3029@utzoo.uucp> I wrote:
>>	(((x & ~0x80808080) - 0x01010101) & 0x80808080)
>>
>>The result is nonzero if, and only if, there was a NUL byte in x...
>
> [ Stuff about needing a filter to detect false alarms deleted ]
>Subversion, n:  a superset     |     Henry Spencer at U of Toronto Zoology
>of a subset.    --J.J. Horning | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

	This does seem like alot of work to test for a null byte...  Has
	anyone considered putting in a test-word-for-byte (twfb?)
	instruction on their favorite processor?  It seems to me that
	adding this kind of a function to an alu would be pretty
	trivial, and it would make a significant improvement in some
	kinds of string operations.  Of course, your strings would have
	to be aligned on word boundaries, but that shouldn't be to
	difficult to add to a compiler.  Has anyone done this sort of
	thing?  Is there any reason not to?  (I haven't designed any
	(real) processors, so it's entirely possible that I'm missing
	out on some major consideration :).

						-Jason

-sig-of-the-day-
"So, Jason, how's that graphics project going?"
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