bdiff: balance recursion to avoid quadratic behavior (issue4704)
For highly structured files like JSON or XML dumps with large numbers
of duplicate lines (eg braces) and isolated matching lines, bdiff
could find large numbers of equally good spans. Because it prefers
earlier matches, this would result in pathologically unbalance
recursion that resulted in quadratic performance.
This patch makes it prefer matches closer to the middle that tend to
balance recursion. This change improves the speed of a pathological
test case from 1100s to 9s.
Included is a smaller test that has a roughly 50x safety margin on the
performance it accepts. It's likely to fail on pure builds because
difflib also has a recursion-balancing problem.
#require eol-in-paths
https://bz.mercurial-scm.org/352
test issue352
$ hg init foo
$ cd foo
$ A=`printf 'he\rllo'`
$ echo foo > "$A"
$ hg add
adding he\r (no-eol) (esc)
llo
abort: '\n' and '\r' disallowed in filenames: 'he\rllo'
[255]
$ hg ci -A -m m
adding he\r (no-eol) (esc)
llo
abort: '\n' and '\r' disallowed in filenames: 'he\rllo'
[255]
$ rm "$A"
$ echo foo > "hell
> o"
$ hg add
adding hell
o
abort: '\n' and '\r' disallowed in filenames: 'hell\no'
[255]
$ hg ci -A -m m
adding hell
o
abort: '\n' and '\r' disallowed in filenames: 'hell\no'
[255]
$ echo foo > "$A"
$ hg debugwalk
f he\r (no-eol) (esc)
llo he\r (no-eol) (esc)
llo
f hell
o hell
o
$ echo bla > quickfox
$ hg add quickfox
$ hg ci -m 2
$ A=`printf 'quick\rfox'`
$ hg cp quickfox "$A"
abort: '\n' and '\r' disallowed in filenames: 'quick\rfox'
[255]
$ hg mv quickfox "$A"
abort: '\n' and '\r' disallowed in filenames: 'quick\rfox'
[255]
https://bz.mercurial-scm.org/2036
$ cd ..
test issue2039
$ hg init bar
$ cd bar
$ cat <<EOF >> $HGRCPATH
> [extensions]
> color =
> [color]
> mode = ansi
> EOF
$ A=`printf 'foo\nbar'`
$ B=`printf 'foo\nbar.baz'`
$ touch "$A"
$ touch "$B"
$ hg status --color=always
\x1b[0;35;1;4m? \x1b[0m\x1b[0;35;1;4mfoo\x1b[0m (esc)
\x1b[0;35;1;4mbar\x1b[0m (esc)
\x1b[0;35;1;4m? \x1b[0m\x1b[0;35;1;4mfoo\x1b[0m (esc)
\x1b[0;35;1;4mbar.baz\x1b[0m (esc)
$ cd ..