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#! /usr/bin/env python3

"""
bitset.py

Written by Geremy Condra

Released 3 May 2009

This module provides a simple bitset implementation
for Python.
"""

from collections import Sequence
import math

class Bitset(Sequence):
"""A very simple bitset implementation for Python.

Note that, like with normal numbers, the leftmost
index is the MSB, and like normal sequences, that
is 0.

Usage:
>>> b = Bitset(5)
>>> b
Bitset(101)
>>> b[:]
[True, False, True]
>>> b[0] = False
>>> b
Bitset(001)
>>> b << 1
Bitset(010)
>>> b >> 1
Bitset(000)
>>> b & 1
Bitset(001)
>>> b | 2
Bitset(011)
>>> b ^ 6
Bitset(111)
>>> ~b
Bitset(110)
"""

value = 0
length = 0

@classmethod
def from_sequence(cls, seq):
"""Iterates over the sequence to produce a new Bitset.

As in integers, the 0 position represents the LSB.
"""
n = 0
for index, value in enumerate(reversed(seq)):
n += 2**index * bool(int(value))
b = Bitset(n)
return b

def __init__(self, value=0, length=0):
"""Creates a Bitset with the given integer value."""
self.value = value
try: self.length = length or math.floor(math.log(value, 2)) + 1
except Exception: self.length = 0

def __and__(self, other):
b = Bitset(self.value & int(other))
b.length = max((self.length, b.length))
return b

def __or__(self, other):
b = Bitset(self.value | int(other))
b.length = max((self.length, b.length))
return b

def __invert__(self):
b = Bitset(~self.value)
b.length = max((self.length, b.length))
return b

def __xor__(self, value):
b = Bitset(self.value ^ int(value))
b.length = max((self.length, b.length))
return b

def __lshift__(self, value):
b = Bitset(self.value << int(value))
b.length = max((self.length, b.length))
return b

def __rshift__(self, value):
b = Bitset(self.value >> int(value))
b.length = max((self.length, b.length))
return b

def __eq__(self, other):
try:
return self.value == other.value
except Exception:
return self.value == other

def __int__(self):
return self.value

def __str__(self):
s = ""
for i in self[:]:
s += "1" if i else "0"
return s

def __repr__(self):
return "Bitset(%s)" % str(self)

def __getitem__(self, s):
"""Gets the specified position.

Like normal integers, 0 represents the MSB.
"""
try:
start, stop, step = s.indices(len(self))
results = []
for position in range(start, stop, step):
pos = len(self) - position - 1
results.append(bool(self.value & (1 << pos)))
return results
except:
pos = len(self) - s - 1
return bool(self.value & (1 << pos))

def __setitem__(self, s, value):
"""Sets the specified position/s to value.

Like normal integers, 0 represents the MSB.
"""
try:
start, stop, step = s.indices(len(self))
for position in range(start, stop, step):
pos = len(self) - position - 1
if value: self.value |= (1 << pos)
else: self.value &= ~(1 << pos)
maximum_position = max((start + 1, stop, len(self)))
self.length = maximum_position
except:
pos = len(self) - s - 1
if value: self.value |= (1 << pos)
else: self.value &= ~(1 << pos)
if len(self) < pos: self.length = pos
return self

def __iter__(self):
"""Iterates over the values in the bitset."""
for i in self[:]:
yield i

def __len__(self):
"""Returns the length of the bitset."""
return self.length