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From: ndiamond@watdaisy.UUCP (Norman Diamond)
Newsgroups: net.puzzle
Subject: Re: 68000 Code Puzzle (spoiler)
Message-ID: <7083@watdaisy.UUCP>
Date: Mon, 18-Mar-85 14:18:59 EST
Article-I.D.: watdaisy.7083
Posted: Mon Mar 18 14:18:59 1985
Date-Received: Tue, 19-Mar-85 03:45:11 EST
References: <1059@decwrl.UUCP> <2830@dartvax.UUCP>
Organization: U of Waterloo, Ontario
Lines: 36

Chuck Simmons writes:
> My puzzle is written in 68000 code, and it does not do anything nearly
> as common as perform a binary search.  (This puzzle is due to Mike Morton,
> the author of the reaganagrams published in a recent Scientific American.)
> d0, d1, and d2 are 32 bit registers.
> 
>         move.w #32,d2   ; d2 = 32
>         bra.s start     ; jump into our loop
> lp:     or.l d1,d0      ; d0 |= d1
> start:  move.l d0,d1    ; d1 = d0
>         add.l #1,d0     ; d0 = d0 + 1
>         dbcs d2,lp      ; if carry is clear, then decrement d2,
>                         ; and if d2 != 0 goto lp.
>                         ; (Thus if the carry is set or if d2 becomes 0,
>                         ; we will leave the loop.)

When the Z80 code puzzle was posted, I mailed to the author instead of
posting a spoiler.  It's nice to see that I figured it out correctly.

If spoilers are really the way to go, here is mine:

The above code counts the 1-bits in the original contents of d0, and
leaves the count in d2.

I'm sorry I don't have another puzzle to suggest (except maybe some code
turned in by third-year students :-) :-( ).

-- 

   Norman Diamond

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