tests/revlog-formatv0.py

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

#!/usr/bin/env python3
# Copyright 2010 Intevation GmbH
# Author(s):
# Thomas Arendsen Hein <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""Create a Mercurial repository in revlog format 0

changeset:   0:a1ef0b125355
tag:         tip
user:        user
date:        Thu Jan 01 00:00:00 1970 +0000
files:       empty
description:
empty file
"""

from __future__ import absolute_import
import binascii
import os
import sys

files = [
    (
        b'formatv0/.hg/00changelog.i',
        b'000000000000004400000000000000000000000000000000000000'
        b'000000000000000000000000000000000000000000000000000000'
        b'0000a1ef0b125355d27765928be600cfe85784284ab3',
    ),
    (
        b'formatv0/.hg/00changelog.d',
        b'756163613935613961356635353036303562366138343738336237'
        b'61623536363738616436356635380a757365720a3020300a656d70'
        b'74790a0a656d7074792066696c65',
    ),
    (
        b'formatv0/.hg/00manifest.i',
        b'000000000000003000000000000000000000000000000000000000'
        b'000000000000000000000000000000000000000000000000000000'
        b'0000aca95a9a5f550605b6a84783b7ab56678ad65f58',
    ),
    (
        b'formatv0/.hg/00manifest.d',
        b'75656d707479006238306465356431333837353835343163356630'
        b'35323635616431343461623966613836643164620a',
    ),
    (
        b'formatv0/.hg/data/empty.i',
        b'000000000000000000000000000000000000000000000000000000'
        b'000000000000000000000000000000000000000000000000000000'
        b'0000b80de5d138758541c5f05265ad144ab9fa86d1db',
    ),
    (b'formatv0/.hg/data/empty.d', b''),
]


def makedirs(name):
    """recursive directory creation"""
    parent = os.path.dirname(name)
    if parent:
        makedirs(parent)
    os.mkdir(name)


makedirs(os.path.join(*'formatv0/.hg/data'.split('/')))

for name, data in files:
    f = open(name, 'wb')
    f.write(binascii.unhexlify(data))
    f.close()

sys.exit(0)