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Re: [JGIT PATCH 03/15] Add IntList as a more efficient representation of List<Integer>

From
Sverre Rabbelier <srabbelier@gmail.com>
Date
Dec 12, 2008, 15:50 UTC
Message-ID
<bd6139dc0812120750j19b4d56an24b9c52a3ca60f20@mail.gmail.com>
In-Reply-To
<20081212154115.GO32487@spearce.org>
On Fri, Dec 12, 2008 at 16:41, Shawn O. Pearce <spearce@spearce.org> wrote:
> If you'd like to send a patch to change it, I'll apply it.  But I
> don't think its worth my time to make this toString() more efficient.

I mainly mentioned it because it's in a Class meant to be more optimal than what Java ships with, but I agree with your reasoning that this toString is not part of what needs to be optimized.

> Other areas of JGit I do try to micro-optimize, because they are
> right smack in the middle of the critical paths.

Hehe, I very much agree with not optimizing prematurely, and if you do optimize to go for it all the way.

> E.g. look at ObjectId.equals(byte[],int,byte[],int). I hand-unrolled
> the memcmp loop because the JIT on x86 does *soooo* much better
> when the code is spelled out:
<code snipped>

Kind of sad that you have to write this kind of code if you want good performance, ah well, perhaps someday... (import java.lang.optimized ;) ).

> This block is in the critical path for any tree diff code, in
> particular for a "git log -- a/" sort of operation.  Its used
> to compare the SHA-1s from two different tree records to see if
> they differ.  Not unrolling this was a huge penalty.
I reckon that is done a lot :). Ashame the JRE can't do that kind of
optimization for you. e.g., if you do:
for(int i = 0; i < constant; i++) {
  some_code;
}
-- 
Cheers,

Sverre Rabbelier
Previous: Shawn O. Pearce
Message 22 of 22 in “More patch parsing support”
  1. 00/15 More patch parsing supportShawn O. Pearce, Dec 12, 2008
  2. 01/15 Correct use of TemporaryBuffer in PatchShawn O. Pearce, Dec 12, 2008
  3. 02/15 Add tests for TemporaryBufferShawn O. Pearce, Dec 12, 2008
  4. 03/15 Add IntList as a more efficient representation of List<Integer>Shawn O. Pearce, Dec 12, 2008
  5. 04/15 Add lineMap computer to RawParseUtils to index locations of line startsShawn O. Pearce, Dec 12, 2008
  6. 05/15 Define FileHeader.PatchType to report the style of patch usedShawn O. Pearce, Dec 12, 2008
  7. 06/15 Test for non-git binary files and mark them as PatchType.BINARYShawn O. Pearce, Dec 12, 2008
  8. 07/15 Set empty patches with no Git metadata to PatchType.BINARYShawn O. Pearce, Dec 12, 2008
  9. 08/15 Always use the FileHeader buffer during Patch.parseHunksShawn O. Pearce, Dec 12, 2008
  10. 09/15 Parse "GIT binary patch" style patch metadataShawn O. Pearce, Dec 12, 2008
  11. 10/15 Record patch parsing errors for later inspection by applicationsShawn O. Pearce, Dec 12, 2008
  12. 11/15 Fix Patch.parse to honor the end point passed inShawn O. Pearce, Dec 12, 2008
  13. 12/15 Correctly handle hunk headers such as "@@ -0,0 +1 @@"Shawn O. Pearce, Dec 12, 2008
  14. 13/15 Patch parse test comparing "git log -p" output to "git log --numstat"Shawn O. Pearce, Dec 12, 2008
  15. 14/15 Abstract the hunk header testing into a methodShawn O. Pearce, Dec 12, 2008
  16. 15/15 Treat "diff --combined" the same as "diff --cc"Shawn O. Pearce, Dec 12, 2008
  17. Robin RosenbergDec 12, 2008
  18. 15/15 Treat "diff --combined" the same as "diff --cc"Shawn O. Pearce, Dec 12, 2008
  19. Shawn O. PearceDec 12, 2008
  20. Sverre RabbelierDec 12, 2008
  21. Shawn O. PearceDec 12, 2008
  22. Sverre RabbelierDec 12, 2008

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