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add get_colliding_prefix_bits, docs and tests

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Victor Shyba 2022-02-22 15:46:08 -03:00
parent 2a1e1d542f
commit af9cc457ec
2 changed files with 37 additions and 0 deletions
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18
lbry/utils.py
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@ -474,3 +474,21 @@ class LockWithMetrics(asyncio.Lock):
return super().release()
finally:
self._lock_held_time_metric.observe(time.perf_counter() - self._lock_acquired_time)
def get_colliding_prefix_bits(first_value: bytes, second_value: bytes, size: int):
"""
Calculates the amount of colliding bits between <first_value> and <second_value> over the <size> first bits.
This is given by the amount of bits that are the same until the first different one (via XOR).
:param first_value: first value to compare, bigger than size.
:param second_value: second value to compare, bigger than size.
:param size: prefix size in bits.
:return: amount of prefix colliding bits.
"""
assert size % 8 == 0, "size has to be a multiple of 8"
size_in_bytes = size // 8
assert len(first_value) >= size_in_bytes, "first_value has to be larger than size parameter"
first_value = int.from_bytes(first_value[:size_in_bytes], "big")
assert len(second_value) >= size_in_bytes, "second_value has to be larger than size parameter"
second_value = int.from_bytes(second_value[:size_in_bytes], "big")
return size - (first_value ^ second_value).bit_length()

19
tests/unit/test_utils.py Normal file
View file

@ -0,0 +1,19 @@
import unittest
from lbry import utils
class UtilsTestCase(unittest.TestCase):
def test_get_colliding_prefix_bits(self):
self.assertEqual(
0, utils.get_colliding_prefix_bits(0xffffff.to_bytes(4, "big"), 0x00000000.to_bytes(4, "big"), 32))
self.assertEqual(
1, utils.get_colliding_prefix_bits(0xefffff.to_bytes(4, "big"), 0x00000000.to_bytes(4, "big"), 32))
self.assertEqual(
8, utils.get_colliding_prefix_bits(0x00ffff.to_bytes(4, "big"), 0x00000000.to_bytes(4, "big"), 16))
self.assertEqual(
8, utils.get_colliding_prefix_bits(0x00ffff.to_bytes(4, "big"), 0x00000000.to_bytes(4, "big"), 8))
self.assertEqual(
1, utils.get_colliding_prefix_bits(0xefffff.to_bytes(4, "big"), 0x00000000.to_bytes(4, "big"), 16))
self.assertEqual(
1, utils.get_colliding_prefix_bits(0xefffff.to_bytes(4, "big"), 0x00000000.to_bytes(4, "big"), 8))