Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!amdcad!weitek!hemingway!robert
From: robert@hemingway.WEITEK.COM (Robert Plamondon)
Newsgroups: comp.arch
Subject: Re: HW v. SW (was RISC v. CISC --more misconceptions)
Message-ID: <745@hemingway.WEITEK.COM>
Date: 10 Nov 88 00:30:46 GMT
References: <156@gloom.UUCP> <18931@apple.Apple.COM> <40@sopwith.UUCP> <998@l.cc.purdue.edu> <1622@scolex> <866@cernvax.UUCP> <7629@aw.sei.cmu.edu>
Reply-To: robert@hemingway.WEITEK.COM (Robert Plamondon)
Organization: WEITEK, Sunnyvale CA
Lines: 25

>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.

The WEITEK XL-Series RISC processors do this in one cycle with the
Perfect Exchange (pexch) instruction, which does field swaps on 2, 4,
8, 16, and 32-bit boundaries. An endian-conversion would be done with

	pexch source, 0b1100, dest # source and dest are registers

a bit-reverse operation (move bit 0 to bit 31, bit 1 to bit 30, etc.)
is done with:

	pexch source, 0b1111, dest

and so on.  Depending on speed grade, this will be done in 1/8 to 1/12
of a microsecond.

	-- Robert
-- 
    Robert Plamondon
    robert@weitek.COM
    "No Toon can resist the old 'Shave and a Hair-Cut'"