Speed tests of various functions for counting the '1' bits in a 32 bit integer in Python 2 or Python 3

bitcount_speed_tests.py

#!/usr/bin/env python3

''' Count bits in a 32 bit Python integer 

    Speed tests of various implementations, mostly
    from http://stackoverflow.com/questions/9829578/fast-way-of-counting-bits-in-python
    
    Some of these functions work on arbitrary input, but some are specifically for
    32 bit integers, see the function sources for detail.

    Written by PM 2Ring 2015.05.22
    Python 2 / 3 version

Loops = 500, Repetitions = 3

bincount
[1.3069090540000161, 1.353041044000065, 1.362490262999927]

bincount_fmt
[1.9206439549998322, 1.9235854250000557, 2.0456352710000374]

count_set_bits
[12.044507647999808, 12.0926836000001, 12.120520207000027]

count_set_bits_a
[12.233064161999891, 12.240866340000139, 12.33954297199989]

number_of_set_bits
[2.0478857069999776, 2.0485297529999116, 2.0935126169999876]

kernighan_bitcount
[6.366286704999993, 6.408641941000042, 7.43474094499993]

count_bits
[2.6552196699999513, 2.6758667039998727, 2.696372879999899]

popcount32_table16
[1.014889951999976, 1.0157701009998163, 1.0245300270000826]

popcount32_table16a
[0.8907187499999054, 0.8914507599999979, 0.943135520000169]

acount16
[0.9405839329999708, 0.94409908800003, 0.9534000090000063]

acount16w
[0.8587064329999521, 0.8790086770000016, 0.8869148689998383]

popcount
[0.2948963090000234, 0.2960135650000666, 0.30662088400003995]
'''

from __future__ import print_function, division
from timeit import Timer
from random import seed, randrange
import array

try:
    from gmpy import popcount
except ImportError:
    print("Can't import gmpy, so can't test gmpy.popcount")
    popcount = None

def bincount(n):
    return bin(n).count("1")

# slightly slower
def bincount_fmt(n):
    return format(n, 'b').count("1")

def count_set_bits(n):
    result = 0
    while n:
        if n & 1: 
            result += 1
        n >>= 1 
    return result

# slightly slower
def count_set_bits_a(n):
    result = 0
    while n:
        result += n & 1
        n >>= 1 
    return result

def kernighan_bitcount(n):
    count = 0
    while n:
        count += 1
        n &= n - 1
    return count

def count_bits(n):
    n = (n & 0x55555555) + ((n & 0xAAAAAAAA) >> 1)
    n = (n & 0x33333333) + ((n & 0xCCCCCCCC) >> 2)
    n = (n & 0x0F0F0F0F) + ((n & 0xF0F0F0F0) >> 4)
    n = (n & 0x00FF00FF) + ((n & 0xFF00FF00) >> 8)
    n = (n & 0x0000FFFF) + ((n ) >> 16)
    return n

def number_of_set_bits(i):
    i = i - ((i >> 1) & 0x55555555)
    i = (i & 0x33333333) + ((i >> 2) & 0x33333333)
    return (((i + (i >> 4) & 0xF0F0F0F) * 0x1010101) & 0xffffffff) >> 24

POPCOUNT_TABLE16 = [0] * 2**16
for index in range(len(POPCOUNT_TABLE16)):
    POPCOUNT_TABLE16[index] = (index & 1) + POPCOUNT_TABLE16[index >> 1]

def popcount32_table16(v):
    return (POPCOUNT_TABLE16[ v        & 0xffff] +
            POPCOUNT_TABLE16[(v >> 16) & 0xffff])

def popcount32_table16a(v):
    return (POPCOUNT_TABLE16[v & 0xffff] +
            POPCOUNT_TABLE16[v >> 16])

typecode = 'H'
atable = array.array(typecode, POPCOUNT_TABLE16)
def acount16(n):
    return atable[n & 0xffff] + atable[n >> 16]

def make_acount():
    atablew = array.array(typecode, POPCOUNT_TABLE16)
    def acount16w(n):
        return atablew[n & 0xffff] + atablew[n >> 16]
    return acount16w

acount16w = make_acount() 

funcs = (
    bincount, 
    #bincount_fmt,
    #count_set_bits,
    #count_set_bits_a,
    #number_of_set_bits,
    #kernighan_bitcount,
    #count_bits,
    #popcount32_table16, 
    popcount32_table16a, 
    #acount16,
    acount16w,
)

if popcount:
    funcs += (popcount,)

seed(137)
nsize = 1024
nums = [randrange(0, 1<<32) for _ in range(nsize)]

def verify():
    ''' Verify that the functions actually perform as intended '''
    print('Verifying...')
    a = [bincount(n) for n in nums]
    for func in funcs[1:]:
        fname = func.__name__
        print('%s' % fname, end=' ')
        print(all(func(n) == a[i] for i, n in enumerate(nums)))
    print()

def time_test(loops, reps):
    ''' Print timing stats for all the functions '''
    print('Timing tests\nLoops = %d, Repetitions = %d' % (loops, reps))

    for func in funcs:
        fname = func.__name__
        print('\n%s' % fname)
        setup = 'from __main__ import nums, %s' % fname
        t = Timer('[%s(n) for n in nums]' % fname, setup)
        r = t.repeat(reps, loops)
        r.sort()
        print(r)

verify()
time_test(loops=500, reps=3)