Hamming Weight

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Benchmark tests of various ways to calculate it are in [hamming_weight_test.lua]:

Lua 5.2.0/bit32, Intel Xeon, 2012-03-22
 hw_simple: 5.9E-06 5.9E-06 5.9E-06 s
 hw_dc2bit: 1.7E-06 1.7E-06 1.7E-06 s
 hw_dc3bit: 1.5E-06 1.5E-06 1.5E-06 s
 hw_dc4bit: 1.8E-06 1.8E-06 1.8E-06 s
    hw_dci: 1.7E-06 1.7E-06 1.7E-06 s
   hw_lut8: 1.2E-06 1.2E-06 1.2E-06 s
  hw_lut8a: 5.4E-07 5.4E-07 5.3E-07 s
 hw_wegner: 2.9E-06 2.9E-06 2.9E-06 s

LuaJIT 2.x/bit git2012-03-17, Intel Xeon, 2012-03-22
 hw_simple: 6.9E-08 6.9E-08 6.9E-08 s
 hw_dc2bit: 1.9E-09 1.9E-09 1.9E-09 s
 hw_dc3bit: 1.8E-09 1.8E-09 1.8E-09 s
 hw_dc4bit: 2.0E-09 2.0E-09 2.0E-09 s
    hw_dci: 1.8E-09 1.8E-09 1.8E-09 s
   hw_lut8: 1.7E-09 1.7E-09 1.7E-09 s
  hw_lut8a: 8.2E-09 8.2E-09 8.2E-09 s
 hw_wegner: 6.0E-08 5.9E-08 5.9E-08 s

(smaller is better)

See Also

• http://en.wikipedia.org/wiki/Hamming_weight