~bzr-pqm/bzr/bzr.dev

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

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

import zlib

import struct

_LeafNode = None

_InternalNode = None

_unknown = None

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', '_')

def _deserialise_leaf_node(bytes, key, search_key_func=None):

    """Deserialise bytes, with key key, into a LeafNode.

    :param bytes: The bytes of the node.

    :param key: The key that the serialised node has.

    """

    global _unknown, _LeafNode, _InternalNode

    if _LeafNode is None:

        from bzrlib import chk_map

        _unknown = chk_map._unknown

        _LeafNode = chk_map.LeafNode

        _InternalNode = chk_map.InternalNode

    result = _LeafNode(search_key_func=search_key_func)

    # Splitlines can split on '\r' so don't use it, split('\n') adds an

    # extra '' if the bytes ends in a final newline.

    lines = bytes.split('\n')

    trailing = lines.pop()

    if trailing != '':

        raise AssertionError('We did not have a final newline for %s'

                             % (key,))

    items = {}

    if lines[0] != 'chkleaf:':

        raise ValueError("not a serialised leaf node: %r" % bytes)

    maximum_size = int(lines[1])

    width = int(lines[2])

    length = int(lines[3])

    prefix = lines[4]

    pos = 5

    while pos < len(lines):

        line = prefix + lines[pos]

        elements = line.split('\x00')

        pos += 1

        if len(elements) != width + 1:

            raise AssertionError(

                'Incorrect number of elements (%d vs %d) for: %r'

                % (len(elements), width + 1, line))

        num_value_lines = int(elements[-1])

        value_lines = lines[pos:pos+num_value_lines]

        pos += num_value_lines

        value = '\n'.join(value_lines)

        items[tuple(elements[:-1])] = value

    if len(items) != length:

        raise AssertionError("item count (%d) mismatch for key %s,"

            " bytes %r" % (length, key, bytes))

    result._items = items

    result._len = length

    result._maximum_size = maximum_size

    result._key = key

    result._key_width = width

    result._raw_size = (sum(map(len, lines[5:])) # the length of the suffix

        + (length)*(len(prefix))

        + (len(lines)-5))

    if not items:

        result._search_prefix = None

        result._common_serialised_prefix = None

    else:

        result._search_prefix = _unknown

        result._common_serialised_prefix = prefix

    if len(bytes) != result._current_size():

        raise AssertionError('_current_size computed incorrectly')

    return result

def _deserialise_internal_node(bytes, key, search_key_func=None):

    global _unknown, _LeafNode, _InternalNode

    if _InternalNode is None:

        from bzrlib import chk_map

        _unknown = chk_map._unknown

        _LeafNode = chk_map.LeafNode

        _InternalNode = chk_map.InternalNode

    result = _InternalNode(search_key_func=search_key_func)

    # Splitlines can split on '\r' so don't use it, remove the extra ''

    # from the result of split('\n') because we should have a trailing

    # newline

    lines = bytes.split('\n')

    if lines[-1] != '':

        raise ValueError("last line must be ''")

    lines.pop(-1)

    items = {}

    if lines[0] != 'chknode:':

        raise ValueError("not a serialised internal node: %r" % bytes)

    maximum_size = int(lines[1])

    width = int(lines[2])

    length = int(lines[3])

    common_prefix = lines[4]

    for line in lines[5:]:

        line = common_prefix + line

        prefix, flat_key = line.rsplit('\x00', 1)

        items[prefix] = (flat_key,)

    if len(items) == 0:

        raise AssertionError("We didn't find any item for %s" % key)

    result._items = items

    result._len = length

    result._maximum_size = maximum_size

    result._key = key

    result._key_width = width

    # XXX: InternalNodes don't really care about their size, and this will

    #      change if we add prefix compression

    result._raw_size = None # len(bytes)

    result._node_width = len(prefix)

    result._search_prefix = common_prefix

    return result