Module: HexaPDF::Utils::BitField

Included in:
Font::TrueType::Table::Head, Font::TrueType::Table::OS2, Type::AcroForm::Field, Type::AcroForm::Form, Type::AcroForm::SignatureField::CertificateSeedValueDictionary, Type::AcroForm::SignatureField::SeedValueDictionary, Type::Annotation, Type::FontDescriptor, Type::OutlineItem
Defined in:
lib/hexapdf/utils/bit_field.rb

Overview

This module is intended to be used to extend class objects. It provides the method #bit_field for declaring a bit field.

Instance Method Summary collapse

Instance Method Details

#bit_field(name, mapping, lister: "#{name}_values", getter: "#{name}_include?", setter: "set_#{name}", unsetter: "unset_#{name}", value_getter: name, value_setter: "self.#{name}") ⇒ Object

Creates a bit field for managing the integer attribute name.

The mapping argument specifies the mapping of names to zero-based bit indices which allows one to use either the bit name or its index when getting or setting. When using an unknown bit name or bit index, an error is raised.

The calling class needs to respond to #name and #name= because these methods are used to get and set the raw integer value; or provide custom method names using the value_getter and value_setter arguments.

After invoking the method the calling class has four new instance methods:

  • NAME_values which returns an array of bit names representing the set bits.

  • NAME_include?(bit) which returns true if the given bit is set.

  • set_NAME(*bits, clear_existing: false) for setting the given bits.

  • unset_NAME(*bits) for clearing the given bits.

The method names can be overridden using the arguments lister, getter, setter and unsetter.



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# File 'lib/hexapdf/utils/bit_field.rb', line 63

def bit_field(name, mapping, lister: "#{name}_values", getter: "#{name}_include?",
              setter: "set_#{name}", unsetter: "unset_#{name}", value_getter: name,
              value_setter: "self.#{name}")
  mapping.default_proc = proc do |h, k|
    if h.value?(k)
      k
    else
      raise ArgumentError, "Invalid bit field name or index '#{k}' for #{self.name}##{name}"
    end
  end

  module_eval(<<-EOF, __FILE__, __LINE__ + 1)
    #{name.upcase}_BIT_MAPPING = mapping.freeze

    def #{lister}
      self.class::#{name.upcase}_BIT_MAPPING.keys.map {|n| #{getter}(n) ? n : nil }.compact
    end

    def #{getter}(bit)
      (#{value_getter} || 0)[self.class::#{name.upcase}_BIT_MAPPING[bit]] == 1
    end

    def #{setter}(*bits, clear_existing: false)
      #{value_setter} = 0 if clear_existing || #{value_getter}.nil?
      result = #{value_getter}
      bits.each {|bit| result |= 1 << self.class::#{name.upcase}_BIT_MAPPING[bit] }
      #{value_setter} =  result
    end

    def #{unsetter}(*bits)
      result = #{value_getter} || 0
      return if result == 0
      bits.each {|bit| result &= ~(1 << self.class::#{name.upcase}_BIT_MAPPING[bit]) }
      #{value_setter} = result
    end
  EOF
end