5fc65d7168
* Replaced all from ...py23 import * with explicit name imports, or removed completely when possible. * Replaced tounicode() with tostr() * Changed all BytesIO ans StringIO imports to from io import ..., replaced all UnicodeIO with StringIO. * Replaced all unichr() with chr() * Misc minor tweaks and fixes
29 lines
795 B
Python
29 lines
795 B
Python
__all__ = ['popCount']
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def popCount(v):
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"""Return number of 1 bits (population count) of an integer.
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If the integer is negative, the number of 1 bits in the
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twos-complement representation of the integer is returned. i.e.
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``popCount(-30) == 28`` because -30 is::
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1111 1111 1111 1111 1111 1111 1110 0010
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Uses the algorithm from `HAKMEM item 169 <https://www.inwap.com/pdp10/hbaker/hakmem/hacks.html#item169>`_.
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Args:
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v (int): Value to count.
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Returns:
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Number of 1 bits in the binary representation of ``v``.
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"""
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if v > 0xFFFFFFFF:
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return popCount(v >> 32) + popCount(v & 0xFFFFFFFF)
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# HACKMEM 169
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y = (v >> 1) & 0xDB6DB6DB
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y = v - y - ((y >> 1) & 0xDB6DB6DB)
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return (((y + (y >> 3)) & 0xC71C71C7) % 0x3F)
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