binary_mask.rb

# frozen_string_literal: true

require 'date'

# Class that holds a date, bit-packed into an integer
class PackedDate
  ## BINARY MASKS AND CONSTANTS
  YEAR_BITS       = 9
  MONTH_BITS      = 5

  YEAR_MASK       = 0b11111111111111000000000
  MONTH_MASK      = 0b00000000000000111100000
  DAY_MASK        = 0b00000000000000000011111

  ZERO_YEAR_MASK  = 0b00000000000000111111111
  ZERO_MONTH_MASK = 0b11111111111111000011111
  ZERO_DAY_MASK   = 0b11111111111111111100000

  def initialize(date)
    pack_date(date)
  end

  def packed
    @packed
  end

  ## PACK BITS
  def self.from_date(date)
    packed = date.year << YEAR_BITS
    packed |= date.month << MONTH_BITS
    packed |= date.day
    new(packed)
  end

  def initialize(packed_date)
    @packed = packed_date
  end

  ## UNPACK BITS
  def year
    (@packed & YEAR_MASK) >> YEAR_BITS
  end

  def month
    (@packed & MONTH_MASK) >> MONTH_BITS
  end

  def day
    (@packed & DAY_MASK)
  end

  def date
    Date.new(year, month, day)
  end

  ## CHANGE BITS
  def year=(new_year)
    @packed = (@packed & ZERO_YEAR_MASK) | (new_year << YEAR_BITS)
  end

  def month=(new_month)
    @packed = (@packed & ZERO_MONTH_MASK) | (new_month << MONTH_BITS)
  end

  def day=(new_day)
    @packed = (@packed & ZERO_DAY_MASK) | new_day
  end
end

date = PackedDate.from_date(Date.today)

packed = date.packed

pd = PackedDate.new(packed)

pd.packed

pd.year

pd.month

pd.day

pd.date