Path: utzoo!utgpu!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!amdcad!crackle!tim
From: tim@crackle.amd.com (Tim Olson)
Newsgroups: comp.arch
Subject: Re: HW v. SW (was RISC v. CISC --more misconceptions)
Message-ID: <23481@amdcad.AMD.COM>
Date: 7 Nov 88 16:47:59 GMT
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Organization: Advanced Micro Devices, Inc. Sunnyvale CA
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In article <866@cernvax.UUCP> hjm@cernvax.UUCP (Hubert Matthews) writes:
| 
| 
| The INMOS T800 has an instruction bitrevword, which turns a
| little-endian word into a big-endian word, effectively doing a
| reflection in the middle.  Great for FFT shuffle routines.  In
| software, it takes quite some time.  In hardware it takes just over 
| 1 microsecond on a 30MHz part.  There is also a bitrevnbits which
| reverses the bottom n bits in a byte and it takes n+4 cycles at 30MHz.
| Again, not very quick in software.

This actually can be done *faster* in software.  1 microsecond @ 30MHz
== 30 cycles, but with an 8-bit table-lookup it can be easily done in
less than 22 cycles.


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