def getprime(nbits):
"""Returns a prime number of max. 'math.ceil(nbits/8)*8' bits. In
other words: nbits is rounded up to whole bytes.
>>> p = getprime(8)
>>> is_prime(p-1)
0
>>> is_prime(p)
1
>>> is_prime(p+1)
0
"""
while True:
integer = read_random_int(nbits)
# Make sure it's odd
integer |= 1
# Test for primeness
if is_prime(integer): break
# Retry if not prime
return integer
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