Source Code for Module Anomos.bitfield

 1  # This program is free software: you can redistribute it and/or modify 
 2  # it under the terms of the GNU General Public License as published by 
 3  # the Free Software Foundation, either version 3 of the License, or 
 4  # (at your option) any later version. 
 5  # 
 6  # This program is distributed in the hope that it will be useful, 
 7  # but WITHOUT ANY WARRANTY; without even the implied warranty of 
 8  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 9  # GNU General Public License for more details. 
10  # 
11  # You should have received a copy of the GNU General Public License 
12  # along with this program.  If not, see <http://www.gnu.org/licenses/>. 
13   
14  # Written by Bram Cohen, Uoti Urpala, and John Hoffman 
15   
16  from array import array 
17   
18  counts = [chr(sum([(i >> j) & 1 for j in xrange(8)])) for i in xrange(256)] 
19  counts = ''.join(counts) 
20   
21   
22 -class Bitfield: 
23   
24 -    def __init__(self, length, bitstring=None): 
25          self.length = length 
26          rlen, extra = divmod(length, 8) 
27          if bitstring is None: 
28              self.numfalse = length 
29              if extra: 
30                  self.bits = array('B', chr(0) * (rlen + 1)) 
31              else: 
32                  self.bits = array('B', chr(0) * rlen) 
33          else: 
34              if extra: 
35                  if len(bitstring) != rlen + 1: 
36                      raise ValueError 
37                  if (ord(bitstring[-1]) << extra) & 0xFF != 0: 
38                      raise ValueError 
39              else: 
40                  if len(bitstring) != rlen: 
41                      raise ValueError 
42              c = counts 
43              self.numfalse = length - sum(array('B', 
44                                                 bitstring.translate(counts))) 
45              if self.numfalse != 0: 
46                  self.bits = array('B', bitstring) 
47              else: 
48                  self.bits = None 
49   
50 -    def __setitem__(self, index, val): 
51          assert val 
52          pos = index >> 3 
53          mask = 128 >> (index & 7) 
54          if self.bits[pos] & mask: 
55              return 
56          self.bits[pos] |= mask 
57          self.numfalse -= 1 
58          if self.numfalse == 0: 
59              self.bits = None 
60   
61 -    def __getitem__(self, index): 
62          bits = self.bits 
63          if bits is None: 
64              return 1 
65          return bits[index >> 3] & 128 >> (index & 7) 
66   
67 -    def __len__(self): 
68          return self.length 
69   
70 -    def tostring(self): 
71          if self.bits is None: 
72              rlen, extra = divmod(self.length, 8) 
73              r = chr(0xFF) * rlen 
74              if extra: 
75                  r += chr((0xFF << (8 - extra)) & 0xFF) 
76              return r 
77          else: 
78              return self.bits.tostring() 
79