~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2007 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""Bisection lookup multiple keys."""

__all__ = [

    'bisect_multi_bytes',

    ]

def bisect_multi_bytes(content_lookup, size, keys):

    """Perform bisection lookups for keys using byte based addressing.

    The keys are looked up via the content_lookup routine. The content_lookup

    routine gives bisect_multi_bytes information about where to keep looking up

    to find the data for the key, and bisect_multi_bytes feeds this back into

    the lookup function until the search is complete. The search is complete

    when the list of keys which have returned something other than -1 or +1 is

    empty. Keys which are not found are not returned to the caller.

    :param content_lookup: A callable that takes a list of (offset, key) pairs

        and returns a list of result tuples ((offset, key), result). Each

        result can be one of:

          -1: The key comes earlier in the content.

          False: The key is not present in the content.

          +1: The key comes later in the content.

          Any other value: A final result to return to the caller.

    :param size: The length of the content.

    :param keys: The keys to bisect for.

    :return: An iterator of the results.

    """

    # possibly make this a generator, but a list meets the contract for now.

    result = []

    delta = size // 2

    search_keys = [(delta, key) for key in keys]

    while search_keys:

        search_results = content_lookup(search_keys)

        if delta > 1:

            delta = delta // 2

        search_keys = []

        for (location, key), status in search_results:

            if status == -1:

                search_keys.append((location - delta, key))

            elif status == 1:

                search_keys.append((location + delta, key))

            elif status == False:

                # not present, stop searching

                continue

            else:

                result.append((key, status))

    return result