Path: utzoo!dciem!nrcaer!scs!spl1!lll-winken!lll-tis!ames!necntc!ima!think!ephraim
From: ephraim@think.COM (ephraim vishniac)
Newsgroups: comp.sys.mac.programmer
Subject: Re: BlockMove efficiency
Message-ID: <21737@think.UUCP>
Date: 7 Jun 88 13:39:28 GMT
Article-I.D.: think.21737
References: <7212@watdragon.waterloo.edu> <8796@dartvax.Dartmouth.EDU>
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Reply-To: ephraim@vidar.think.com.UUCP (ephraim vishniac)
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In article <8796@dartvax.Dartmouth.EDU> earleh@eleazar.dartmouth.edu (Earle R. Horton) writes:
>BlockMove isn't bad for general purpose use, and I probably couldn't
>do better.  For specific cases, however, there is certainly room for
>speed improvement.  BlockMove uses "move.b" for all moves, and strings
>a few of them together to gain a speed increase over a loop.  If you
>are moving WORDs (integers, shorts, what have you) then you can move
>them much faster using "move.w" or "move.l".  If you are moving
>LONGINTs, then you can move them a lot faster on a Mac II if they are
>aligned properly and you use "move.l."

Earle, the last time I disassembled _BlockMove (back in 64K ROM days),
the description you give above was wrong.  Unless someone at Apple has
completely lost his mind, I expect it's still wrong.

BlockMove checks on the relative alignment of the source and
destination.  When possible, it does bulk moves by saving off most of
the registers, then doing large MOVEM.L's to read/write as much data
as possible at each pass.  I seem to recall a four-instruction loop:
one to read from memory to registers; one to write from registers to
memory; one to fix up an address pointer because MOVEM has limited
choice of pre/post increment/decrement; and a dbra for loop control.

What's the source of your claim?


Ephraim Vishniac					  ephraim@think.com
Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214

     On two occasions I have been asked, "Pray, Mr. Babbage, if you put
     into the machine wrong figures, will the right answers come out?"