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# Copyright 2011 Lars Wirzenius
#
# 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 3 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, see <http://www.gnu.org/licenses/>.
import os
class IdPath(object):
'''Convert a numeric id to a pathname.
The ids are stored in a directory hierarchy, the depth of which
can be adjusted by a parameter to the class. The ids are assumed
to be non-negative integers.
'''
def __init__(self, dirname, depth, bits_per_level, skip_bits):
self.dirname = dirname
self.depth = depth
self.bits_per_level = bits_per_level
self.skip_bits = skip_bits
def convert(self, identifier):
def level_bits(level):
level_mask = 2**self.bits_per_level - 1
n = self.skip_bits + level * self.bits_per_level
return (identifier >> n) & level_mask
subdirs = ['%d' % level_bits(i) for i in range(self.depth)]
parts = [self.dirname] + subdirs + ['%x' % identifier]
return os.path.join(*parts)
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