Canonicalize CIDR: Difference between revisions

===Bit mask and shift===

<lang python>"""Canonicalize CIDR"""

DIGITS = (24, 16, 8, 0)

def dotted_to_int(dotted: str) -> int:

digits = [int(digit) for digit in dotted.split(".")]

return sum(a << b for a, b in zip(digits, DIGITS))

def int_to_dotted(ip: int) -> str:

digits = [(ip & (255 << d)) >> d for d in DIGITS]

return ".".join(str(d) for d in digits)

def network_mask(number_of_bits: int) -> int:

return ((1 << number_of_bits) - 1) << (32 - number_of_bits)

def canonicalize(ip: str) -> str:

dotted, network_bits = ip.split("/")

i = dotted_to_int(dotted)

mask = network_mask(int(network_bits))

return int_to_dotted(i & mask) + "/" + network_bits

TEST_CASES = [

("36.18.154.103/12", "36.16.0.0/12"),

("62.62.197.11/29", "62.62.197.8/29"),

("67.137.119.181/4", "64.0.0.0/4"),

("161.214.74.21/24", "161.214.74.0/24"),

("184.232.176.184/18", "184.232.128.0/18"),

]

if __name__ == "__main__":

for ip, expect in TEST_CASES:

rv = canonicalize(ip)

print(f"{ip:<18} -> {rv}")

assert rv == expect

</lang>

{{out}}

<pre>

36.18.154.103/12 -> 36.16.0.0/12

62.62.197.11/29 -> 62.62.197.8/29

67.137.119.181/4 -> 64.0.0.0/4

161.214.74.21/24 -> 161.214.74.0/24

184.232.176.184/18 -> 184.232.128.0/18

</pre>