near_power_of_two.py

def near_power_of_two(v):
  if v < 0:
    return 0

  if v == 0:
    return 0

  v -= 1
  count = 0
  while v != 0:
    v = v >> 1
    count += 1
  return 2**count

print(near_power_of_two(0))
print(near_power_of_two(1))
print(near_power_of_two(2))
print(near_power_of_two(3))
print(near_power_of_two(4))
print(near_power_of_two(31))
print(near_power_of_two(32))
print(near_power_of_two(33))

"""output
0
1
2
4
4
32
32
64
"""

2の冪

1, 2, 4, 8, 16, 32, 64, 128, 256, 512,・・・

2**16

65536

2**32

4294967296