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From: baum@apple.UUCP
Newsgroups: comp.arch,comp.lang.c
Subject: Re: String Processing Instruction
Message-ID: <563@apple.UUCP>
Date: Wed, 25-Mar-87 21:24:19 EST
Article-I.D.: apple.563
Posted: Wed Mar 25 21:24:19 1987
Date-Received: Fri, 27-Mar-87 07:03:27 EST
References: <15292@amdcad.UUCP>
Reply-To: baum@apple.UUCP (Allen Baum)
Organization: Apple Computer, Inc.
Lines: 26
Xref: utgpu comp.arch:664 comp.lang.c:1334

--------
[]
>
>One unique feature of the Am29000 architecture is a special instruction.
>This instruction is intended to be used to speed-up string processing,
>but my guess is that other uses will be discovered.  The instruction is
>called "compare-bytes" and works like this:.....

The HP Spectrum has three instructions that are very similar.
 Unit XOR will Exlusive-OR two registers and let you skip if any byte or
   halfword is equal or not equal.

 Unit AddComplement[&Trap on Condition] will add the ones complement of
   one register to another. This is sort of subtraction without the forced
   carry. That way, all bytes, halfwords & nibbles essentially have the
   same carry-in (although a carry out of one stage could force a carry-in
   to another, it turns out this doesn't affect the major uses of the 
   instruction). Then, either a trap will occur or the next instruction will
   be skipped if the conditions are met. The conditions are any halfword/
   byte/nibble carry, any halfword/byte zero, and their complements.

Among other things, these instructions can be used for string searching a
word at a time, decimal/byte/halfword range checking/validation a byte at
a time, and decimal addition pre-biasing.

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