/brz/remove-bazaar

# Copyright (C) 2009 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Python implementation of _search_key functions, etc."""

import zlib

import struct

def _crc32(bit):

    # Depending on python version and platform, zlib.crc32 will return either a

    # signed (<= 2.5 >= 3.0) or an unsigned (2.5, 2.6).

    # http://docs.python.org/library/zlib.html recommends using a mask to force

    # an unsigned value to ensure the same numeric value (unsigned) is obtained

    # across all python versions and platforms.

    # Note: However, on 32-bit platforms this causes an upcast to PyLong, which

    #       are generally slower than PyInts. However, if performance becomes

    #       critical, we should probably write the whole thing as an extension

    #       anyway.

    #       Though we really don't need that 32nd bit of accuracy. (even 2**24

    #       is probably enough node fan out for realistic trees.)

    return zlib.crc32(bit)&0xFFFFFFFF

def _search_key_16(key):

    """Map the key tuple into a search key string which has 16-way fan out."""

    return '\x00'.join(['%08X' % _crc32(bit) for bit in key])

def _search_key_255(key):

    """Map the key tuple into a search key string which has 255-way fan out.

    We use 255-way because '\n' is used as a delimiter, and causes problems

    while parsing.

    """

    bytes = '\x00'.join([struct.pack('>L', _crc32(bit)) for bit in key])

    return bytes.replace('\n', '_')