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KrzysztofCiba/popcntLUT.py

Created June 9, 2013 19:26
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popcntLUT.py
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popcntLUT.py
## bit count look up table in range 0..255
__bcLUT = [ 0 ] * 256
for i in range(256):
__bcLUT[i] = ( i & 1 ) + __bcLUT[i/2]
def popcntLUT( arg ):
""" popcnt using look up table """
assert type(arg) in ( int, long )
return sum( [ __bcLUT[ ( arg >> i ) & 255 ]
for i in range( 0, arg.bit_length(), 8 ) ] )
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