Class: VariantAssigner

Inherits:
Object
  • Object
show all
Defined in:
lib/variant_assigner.rb

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(key) ⇒ VariantAssigner

Returns a new instance of VariantAssigner.



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# File 'lib/variant_assigner.rb', line 9

def initialize(key)
  md5 = Hashing.hash_unit(key.to_s)
  @key = MurmurHash3::V32.str_hash(md5)
  @normalizer = 1.0 / 0xffffffff
end

Instance Attribute Details

#key ⇒ Object (readonly)

Returns the value of attribute key.



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# File 'lib/variant_assigner.rb', line 7

def key
  @key
end

Class Method Details

.choose_variant(split, prob) ⇒ Object 



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# File 'lib/variant_assigner.rb', line 26

def self.choose_variant(split, prob)
  sum = 0
  split.each_with_index do |s, i|
    sum += s
    return i if prob < sum
  end

  split.count - 1
end

Instance Method Details

#assign(split, seed_hi, seed_lo) ⇒ Object 



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# File 'lib/variant_assigner.rb', line 36

def assign(split, seed_hi, seed_lo)
  prob = probability(seed_hi, seed_lo)
  self.class.choose_variant(split, prob)
end

#probability(seed_hi, seed_lo) ⇒ Object 



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# File 'lib/variant_assigner.rb', line 15

def probability(seed_hi, seed_lo)
  buffer = Array.new
  put_uint32(buffer, seed_lo)
  put_uint32(buffer, seed_hi)
  put_uint32(buffer, key)
  hash = MurmurHash3::V32.str_hash(buffer.pack("C*"))

  prob = (hash & 0xffffffff) * @normalizer
  prob
end

#put_uint32(buffer, x) ⇒ Object 



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# File 'lib/variant_assigner.rb', line 41

def put_uint32(buffer, x)
  buffer << (x & 0xff)
  buffer << ((x >> 8) & 0xff)
  buffer << ((x >> 16) & 0xff)
  buffer << ((x >> 24) & 0xff)
end