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encoding: fix trim() to be O(n) instead of O(n^2)...

encoding: fix trim() to be O(n) instead of O(n^2) `encoding.trim()` iterated over the possible lengths smaller than the input and created a slice for each. It then calculated the column width of the result, which is of course O(n), so the overall algorithm was O(n). This patch rewrites it to iterate over the unicode characters, keeping track of the length so far. Also, the old algorithm started from the end of the string, which made it much worse when the input is large and the limit is small (such as the typical 72 we pass to it). You can time it by running something like this: ``` time python3 -c 'from mercurial.utils import stringutil; print(stringutil.ellipsis(b"0123456789" * 1000, 5))' ``` That drops from 4.05 s to 83 ms with this patch (and most of that is of course startup time). Differential Revision: https://phab.mercurial-scm.org/D12089

Augie Fackler - - Load All Authors

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        Augie Fackler
    
fuzz: add a quick README to try and document how to test new fuzzers...

              r36698
            
      How to add fuzzers (partially cribbed from oss-fuzz[0]):

        1) git clone https://github.com/google/oss-fuzz

        2) cd oss-fuzz

        3) python infra/helper.py build_image mercurial

        4) docker run --cap-add=SYS_PTRACE -it -v $HG_REPO_PATH:/hg-new \

               gcr.io/oss-fuzz/mercurial bash

        5) cd /src

        6) rm -r mercurial

        7) ln -s /hg-new mercurial

        8) cd mercurial

        9) compile

        Augie Fackler
    
fuzz: add some more docs about building/running fuzzers...

              r36716
            
        10) ls $OUT

      Step 9 is literally running the command "compile", which is part of

      the docker container. Once you have that working, you can build the

      fuzzers like this (in the oss-fuzz repo):

      python infra/helper.py build_fuzzers --sanitizer address mercurial $HG_REPO_PATH

      (you can also say "memory", "undefined" or "coverage" for

      sanitizer). Then run the built fuzzers like this:

      python infra/helper.py run_fuzzer mercurial -- $FUZZER

        Augie Fackler
    
fuzz: add a quick README to try and document how to test new fuzzers...

              r36698
            
      0: https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md

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Augie Fackler fuzz: add a quick README to try and document how to test new fuzzers...	r36698	How to add fuzzers (partially cribbed from oss-fuzz[0]):

		1) git clone https://github.com/google/oss-fuzz
		2) cd oss-fuzz
		3) python infra/helper.py build_image mercurial
		4) docker run --cap-add=SYS_PTRACE -it -v $HG_REPO_PATH:/hg-new \
		gcr.io/oss-fuzz/mercurial bash
		5) cd /src
		6) rm -r mercurial
		7) ln -s /hg-new mercurial
		8) cd mercurial
		9) compile
Augie Fackler fuzz: add some more docs about building/running fuzzers...	r36716	10) ls $OUT

		Step 9 is literally running the command "compile", which is part of
		the docker container. Once you have that working, you can build the
		fuzzers like this (in the oss-fuzz repo):

		python infra/helper.py build_fuzzers --sanitizer address mercurial $HG_REPO_PATH

		(you can also say "memory", "undefined" or "coverage" for
		sanitizer). Then run the built fuzzers like this:

		python infra/helper.py run_fuzzer mercurial -- $FUZZER
Augie Fackler fuzz: add a quick README to try and document how to test new fuzzers...	r36698
		0: https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md