~bzr-pqm/bzr/bzr.dev

2890.2.3 by Robert Collins
* New module ``bzrlib.bisect_multi`` with generic multiple-bisection-at-once
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# Copyright (C) 2007 Canonical Ltd
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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"""Bisection lookup multiple keys."""
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__all__ = [
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    'bisect_multi_bytes',
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    ]
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def bisect_multi_bytes(content_lookup, size, keys):
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    """Perform bisection lookups for keys using byte based addressing.
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    The keys are looked up via the content_lookup routine. The content_lookup
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    routine gives bisect_multi_bytes information about where to keep looking up
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    to find the data for the key, and bisect_multi_bytes feeds this back into
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    the lookup function until the search is complete. The search is complete
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    when the list of keys which have returned something other than -1 or +1 is
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    empty. Keys which are not found are not returned to the caller.
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    :param content_lookup: A callable that takes a list of (offset, key) pairs
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        and returns a list of result tuples ((offset, key), result). Each
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        result can be one of:
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          -1: The key comes earlier in the content.
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          False: The key is not present in the content.
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          +1: The key comes later in the content.
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          Any other value: A final result to return to the caller.
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    :param size: The length of the content.
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    :param keys: The keys to bisect for.
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    :return: An iterator of the results.
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    """
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    # possibly make this a generator, but a list meets the contract for now.
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    result = []
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    delta = size // 2
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    search_keys = [(delta, key) for key in keys]
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    while search_keys:
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        search_results = content_lookup(search_keys)
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        if delta > 1:
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            delta = delta // 2
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        search_keys = []
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        for (location, key), status in search_results:
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            if status == -1:
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                search_keys.append((location - delta, key))
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            elif status == 1:
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                search_keys.append((location + delta, key))
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            elif status == False:
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                # not present, stop searching
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                continue
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            else:
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                result.append((key, status))
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    return result