Counting bits (4bytes integer)

bitcounting.py

# coding: utf-8

# In[196]:

import timeit


# In[197]:

codebook = [ bin(_).count("1") for _ in xrange(0xff) ]


# In[198]:

def only_codebook(n):
    if n <= 0xff:
        return codebook[n]
    elif n <= 0xffff:
        return codebook[n & 0xff] + codebook[ n>>8 ]
    elif n <= 0xffffff:
        return codebook[n & 0xff] + codebook[ (n>>8) & 0xff ] + codebook[ (n>>16) & 0xff ]
    else:
        return codebook[n & 0xff] + codebook[ (n>>8) & 0xff ] + codebook[ (n>>16) & 0xff ] + codebook[ (n>>24) & 0xff ]        


# In[199]:

def only_bitshift(n):
    c = 0
    for _ in xrange(32):
        if n & 1 == 1:
            c+=1
        n = n >> 1
    return c


# In[200]:

def mix_codebook_bitshift(n):
    c = 0
    for _ in xrange(4):
        c+=codebook[n&0xff]
        n = n >> 8
    return c


# In[201]:

def bin2stringcount(n):
    return bin(n).count("1")

def and_plus(n):
    c = 0
    while n:
        n&=n-1
        c+=1
    return c

# In[202]:

N = 0xffff+3


# In[207]:

get_ipython().magic(u'timeit bin2stringcount(N)')


# In[208]:

get_ipython().magic(u'timeit only_codebook(N)')


# In[209]:

get_ipython().magic(u'timeit only_bitshift(N)')


# In[210]:

get_ipython().magic(u'timeit mix_codebook_bitshift(N)')

# In[211]:

get_ipython().magic(u'timeit and_plus(N)')