Re: Speed Traps
Re: Speed Traps
- Subject: Re: Speed Traps
- From: publiclook <email@hidden>
- Date: Wed, 14 May 2003 21:14:39 -0400
Don't guess about what takes time. You have already wasted you
programming time needlessly. Profile your code and then you will KNOW
where the time is being spent and you can optimize only the places that
will give maximum benefit.
See Sampler and gprof that are already on your hard disk.
On Wednesday, May 14, 2003, at 06:07 PM, John Nairn wrote:
I spent a day rewriting a custom expression parcer for what I hoped
would give me much more speed but the final result is now slower. It
is hard to believe it is slower; could I be missing some Cocoa speed
traps?
First version parced a NSString expression and evaluated as it went.
New version tokenizes the expression on the first past and then all
subsequent passes do no parcing, but just evaluate using the tokens.
The new version evaluation with tokens is slower than the first
version that parced AND evaluated on every pass. It does not make
sense and I am hoping I missed something or am using some Cocoa
feature in new version that is cause speed hang up?
One finding and maybe clue to speed traps:
In evaluating from tokens for expressions with groupings, I recursive
pass sub arrays of tokens to a function. If I allocate the sub arrays
and release them it it is slower than using autoreleased arrays. In
other words
subExpr=[[NSMutableArray alloc] initWithArray:...]
evaluate
[subExpr release];
is noticeably slower than
subExpr=[NSMutableArray arrayWithArray:...]
evaluate
I used the former method because I was concerned this large
calculation would be building up a large pool of autoreleased objects
(several hundred thousand) and slowing things down. I guess that was
wrong.
------------
John Nairn (1-801-581-3413, FAX: 1-801-581-4816)
Web page: http://www.mse.utah.edu/~nairn
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| References: | |
| | >Speed Traps (From: John Nairn <email@hidden>) |