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Re: [PATCH] fix for diff optimization bug

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: Mon, 24 Dec 2012 20:51:09 +0000 (GMT)

Hi, Hideki.  Thank you very much for finding this bug and a fix for it.
You might be interested to know that on the 'trunk', a new test has already been added for a similar problem:

$ ./subversion/tests/libsvn_diff/diff-diff3-test --list
[...]
  13    XFAIL  difference at the start of a 128KB window

We don't have a fix for this bug yet.  I don't know whether this bug also exists in version 1.7.8.

It would be very useful to have a regression test for the bug that you have found.  Would you be able to convert your reproduction recipe into a regression test written in C like the that one on trunk?
Please let us know if you would be willing to write a test for the bug you found, and/or port test 13 to version 1.7, and/or write a patch to fix the bug shown by test number 13.  We can treat them as two entirely separate problems, but maybe you have the skill and wish to help fix both of them.

- Julian

Hideki IWAMOTO wrote:

> The optimization of diff inclued in version 1.7 has a bug that
> produces incorrect diff on a certain condition.
> The attached patch fix it.
>
>
> Detail of the bug
> -----------------
>
> When the identical suffix begins at the boundary of a chunk,
> datasource_get_next_token() defined in subversion/libsvn_diff/diff_file.c
> does not stop at head of the identical suffix.
> Therefore, when one of the identical suffixes of the original file
> and the modified file begin from the boundary of a chunk,
> excessive tokens are added to the diff tree.
>
> How to reproduce
> ----------------
>
> $ for ((i=0;i<8256;i++)); do echo 0123456789abcde; done > test.txt
> $ hexdump -C test.txt
> 00000000  30 31 32 33 34 35 36 37  38 39 61 62 63 64 65 0a  |0123456789abcde.|
> *
> 00020400
> $ svn add test.txt; svn ci -m test
> A        test.txt
> Adding        test.txt
> Transmitting file data .
> Committed revision 2.
> $ echo 0123456789ABCDE |dd of=test.txt bs=16 seek=64 conv=notrunc
> 1+0 records in
> 1+0 records out
> $ echo 0123456789ABCDE |dd of=test.txt bs=16 seek=8141 conv=notrunc
> 1+0 records in
> 1+0 records out
> $ echo 0123456789abcde >> test.txt
> $ echo 0123456789abcde >> test.txt
> $ hexdump -C test.txt
> 00000000  30 31 32 33 34 35 36 37  38 39 61 62 63 64 65 0a  |0123456789abcde.|
> *
> 00000400  30 31 32 33 34 35 36 37  38 39 41 42 43 44 45 0a  |0123456789ABCDE.|
> 00000410  30 31 32 33 34 35 36 37  38 39 61 62 63 64 65 0a  |0123456789abcde.|
> *
> 0001fcd0  30 31 32 33 34 35 36 37  38 39 41 42 43 44 45 0a  |0123456789ABCDE.|
> 0001fce0  30 31 32 33 34 35 36 37  38 39 61 62 63 64 65 0a  |0123456789abcde.|
> *
> 00020420
> $ svn cat test.txt | diff -u - test.txt
> --- -  2012-12-24 22:30:18.760832000 +0900
> +++ test.txt    2012-12-24 22:29:24.000000000 +0900
> @@ -62,6 +62,7 @@
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> +0123456789ABCDE
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> @@ -8138,6 +8139,7 @@
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> +0123456789ABCDE
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> $ svn di test.txt
> Index: test.txt
> ===================================================================
> --- test.txt    (revision 2)
> +++ test.txt    (working copy)
> @@ -62,6 +62,7 @@
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> +0123456789ABCDE
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> @@ -8138,6 +8139,7 @@
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> +0123456789ABCDE
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> @@ -8188,6 +8190,72 @@
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> +0123456789abcde
> 0123456789abcde
> 0123456789abcde
> 0123456789abcde
>
>
> --
> Hideki IWAMOTO <h-iwamoto_at_kit.hi-ho.ne.jp>
>
Received on 2012-12-24 21:51:45 CET

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