Python/bit_manipulation/count_number_of_one_bits.py

92 lines
2.7 KiB
Python
Raw Normal View History

from timeit import timeit
def get_set_bits_count_using_brian_kernighans_algorithm(number: int) -> int:
"""
Count the number of set bits in a 32 bit integer
>>> get_set_bits_count_using_brian_kernighans_algorithm(25)
3
>>> get_set_bits_count_using_brian_kernighans_algorithm(37)
3
>>> get_set_bits_count_using_brian_kernighans_algorithm(21)
3
>>> get_set_bits_count_using_brian_kernighans_algorithm(58)
4
>>> get_set_bits_count_using_brian_kernighans_algorithm(0)
0
>>> get_set_bits_count_using_brian_kernighans_algorithm(256)
1
>>> get_set_bits_count_using_brian_kernighans_algorithm(-1)
Traceback (most recent call last):
...
ValueError: the value of input must not be negative
"""
if number < 0:
raise ValueError("the value of input must not be negative")
result = 0
while number:
number &= number - 1
result += 1
return result
def get_set_bits_count_using_modulo_operator(number: int) -> int:
"""
Count the number of set bits in a 32 bit integer
>>> get_set_bits_count_using_modulo_operator(25)
3
>>> get_set_bits_count_using_modulo_operator(37)
3
>>> get_set_bits_count_using_modulo_operator(21)
3
>>> get_set_bits_count_using_modulo_operator(58)
4
>>> get_set_bits_count_using_modulo_operator(0)
0
>>> get_set_bits_count_using_modulo_operator(256)
1
>>> get_set_bits_count_using_modulo_operator(-1)
Traceback (most recent call last):
...
ValueError: the value of input must not be negative
"""
if number < 0:
raise ValueError("the value of input must not be negative")
result = 0
while number:
if number % 2 == 1:
result += 1
number >>= 1
return result
def benchmark() -> None:
"""
Benchmark code for comparing 2 functions, with different length int values.
Brian Kernighan's algorithm is consistently faster than using modulo_operator.
"""
def do_benchmark(number: int) -> None:
setup = "import __main__ as z"
print(f"Benchmark when {number = }:")
print(f"{get_set_bits_count_using_modulo_operator(number) = }")
timing = timeit("z.get_set_bits_count_using_modulo_operator(25)", setup=setup)
print(f"timeit() runs in {timing} seconds")
print(f"{get_set_bits_count_using_brian_kernighans_algorithm(number) = }")
timing = timeit(
"z.get_set_bits_count_using_brian_kernighans_algorithm(25)",
setup=setup,
)
print(f"timeit() runs in {timing} seconds")
for number in (25, 37, 58, 0):
do_benchmark(number)
print()
if __name__ == "__main__":
import doctest
doctest.testmod()
benchmark()