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from bitarray import bitarray
from bitarray.util import int2ba, ba2int, pprint
class SmallIntArray(object):
"""
Class which allows efficiently storing an array of integers
represented by a specified number of bits.
For example, an array with 1000 5 bit integers can be created,
allowing each element in the array to take values form 0 to 31,
while the size of the object is 625 (5000/8) bytes.
"""
def __init__(self, N, k):
self.N = N # number of integers
self.k = k # bits for each integer
self.array = bitarray(N * k)
def slice_i(self, i):
assert 0 <= i < self.N
return slice(self.k * i, self.k * (i + 1))
def __getitem__(self, i):
return ba2int(self.array[self.slice_i(i)])
def __setitem__(self, i, v):
self.array[self.slice_i(i)] = int2ba(v, self.k)
if __name__ == '__main__':
from random import randrange
# define array with 1000 integers, each represented by 5 bits
a = SmallIntArray(1000, 5)
b = [] # store values, for assertion below
for i in range(1000):
v = randrange(32)
b.append(v)
a[i] = v
print(b[:5])
print(a.array.buffer_info())
pprint(a.array[:25], group=5)
for i in range(1000):
assert a[i] == b[i]
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