Path: utzoo!attcan!uunet!portal!cup.portal.com!bcase
From: bcase@cup.portal.com (Brian bcase Case)
Newsgroups: comp.arch
Subject: Re: HW v. SW (was RISC v. CISC --more misconceptions)
Message-ID: <11066@cup.portal.com>
Date: 8 Nov 88 07:33:07 GMT
References: <156@gloom.UUCP> <18931@apple.Apple.COM> <40@sopwith.UUCP> <998
Organization: The Portal System (TM)
Lines: 12

>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.

It must be slimilar for other RISCs (the T800 is not my idea, but...),
but for the 29K, this takes at most 13 instructions or 0.520 microsecond
on a 25 MHz part.  I am sure that a better algorithm can be found that
the one that I thought of in 15 seconds.