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From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.m68k
Subject: Re: Recent Motorola ad seen in Byte
Message-ID: <8705031814.AA01450@cory.Berkeley.EDU>
Date: Sun, 3-May-87 14:14:49 EDT
Article-I.D.: cory.8705031814.AA01450
Posted: Sun May  3 14:14:49 1987
Date-Received: Sun, 3-May-87 20:18:57 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 26

>>1. how would you code a string instruction like FFS (find first set bit)
>>   to fit in something like the 68010's single instruction looping
>>   feature/cache?
>
>	moveq.l	#31,D0
>	move.l 	ea,D1
>loop	asl.l	#1,D1
>	dbcs 	loop

	It also occurs to me that one could use a 256 byte lookup table and
then make the string length arbitrary:

	move.l	string_base,A0
	move.l	table_lookup_base,A1
	clr.l	D0
loop	move.b	(A0)+,D0
	move.b	0(A1+D0.W),D1
	beq	loop
	(D1 contains bit number.  If you want to stop at a \0, simply load
	 table entry 0 with some illegal bit number like $FF)

	Although this does not use a DBcc, and takes about 270 bytes more 
memory, it is quite a bit faster than the DBcc since we are checking bits
a byte at a time.

				-Matt