Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!amdcad!crackle!tim
From: tim@crackle.amd.com (Tim Olson)
Newsgroups: comp.arch
Subject: Re: RISC v. CISC --more misconceptions
Message-ID: <23449@amdcad.AMD.COM>
Date: 2 Nov 88 18:34:56 GMT
References: <156@gloom.UUCP> <18931@apple.Apple.COM> <40@sopwith.UUCP> <998@l.cc.purdue.edu> <7575@aw.sei.cmu.edu>
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Reply-To: tim@crackle.amd.com (Tim Olson)
Organization: Advanced Micro Devices, Inc. Sunnyvale CA
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In article <7575@aw.sei.cmu.edu> firth@bd.sei.cmu.edu (Robert Firth) writes:
| In article <998@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
| >There are many other operations which are cheap in hardware and expensive in
| >software...I will toss in a few for starters.
| 
| >	Find the distance to the next one in a bit stream FAST.  It would
| >be good to have an exception handler if one is not found.  I am considering
| >algorithms not worth implementing if the operation is slow.
| 
| This is implemented in hardware on the MC68020 by the 'BFFFO' instruction.
| It takes 18 cycles to find the first bit in a 32-bit register, and upto
| 32 cycles to find the first bit in a 32-bit bitfield in memory.

"hardware"?  Well, microcode anyway.  If it were implemented in
hardware, it can be done in a single cycle, as it is on the Am29000 with
the CLZ (Count Leading Zeros) instruction.

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