Module: BitsCount::Primitive

Defined in:
lib/bits_count/primitive.rb

Constant Summary collapse

UNPACK_PATTERN = 
"B*"
WORDBITS = 
Hash[0.upto(2**16-1).map{|i| [i, population_count_int32(i)] }].freeze

Class Method Summary collapse

Class Method Details

.population_count_int32(i) ⇒ Object 



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# File 'lib/bits_count/primitive.rb', line 8

def population_count_int32(i)
  i = i - ((i >> 1) & 0x55555555)
  i = (i & 0x33333333) + ((i >> 2) & 0x33333333)
  i = (i + (i >> 4)) & 0x0F0F0F0F
  i = i + (i >> 8)
  i = i + (i >> 16)
  i & 0x0000003F
end

.population_count_map(i) ⇒ Object 



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# File 'lib/bits_count/primitive.rb', line 22

def population_count_map(i)
  WORDBITS[i&0xFFFF] + WORDBITS[i>>16]
end

.population_count_str(s) ⇒ Object 



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# File 'lib/bits_count/primitive.rb', line 18

def population_count_str(s)
  s.unpack(UNPACK_PATTERN).first.count(?1)
end