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'''Functions for generating random numbers.'''
import math
import os
import random
import rsa.transform
def read_random_int(nbits):
"""Reads a random integer of approximately nbits bits rounded up to whole
bytes
"""
nbytes = int(math.ceil(nbits/8.))
randomdata = os.urandom(nbytes)
return rsa.transform.bytes2int(randomdata)
def randint(minvalue, maxvalue):
"""Returns a random integer x with minvalue <= x <= maxvalue"""
# Safety - get a lot of random data even if the range is fairly
# small
min_nbits = 32
# The range of the random numbers we need to generate
range = (maxvalue - minvalue) + 1
# Which is this number of bytes
rangebytes = (rsa.transform.bit_size(range) + 7) / 8
# Convert to bits, but make sure it's always at least min_nbits*2
rangebits = max(rangebytes * 8, min_nbits * 2)
# Take a random number of bits between min_nbits and rangebits
nbits = random.randint(min_nbits, rangebits)
return (read_random_int(nbits) % range) + minvalue
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