Python/bit_manipulation/find_previous_power_of_two.py

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def find_previous_power_of_two(number: int) -> int:
"""
Find the largest power of two that is less than or equal to a given integer.
https://stackoverflow.com/questions/1322510
>>> [find_previous_power_of_two(i) for i in range(18)]
[0, 1, 2, 2, 4, 4, 4, 4, 8, 8, 8, 8, 8, 8, 8, 8, 16, 16]
>>> find_previous_power_of_two(-5)
Traceback (most recent call last):
...
ValueError: Input must be a non-negative integer
>>> find_previous_power_of_two(10.5)
Traceback (most recent call last):
...
ValueError: Input must be a non-negative integer
"""
if not isinstance(number, int) or number < 0:
raise ValueError("Input must be a non-negative integer")
if number == 0:
return 0
power = 1
while power <= number:
power <<= 1 # Equivalent to multiplying by 2
return power >> 1 if number > 1 else 1
if __name__ == "__main__":
import doctest
doctest.testmod()