Module: Zippo::BinaryStructure::CodeGen

Defined in:
lib/zippo/binary_structure/meta.rb

Overview

Profiling shows most of our time is spent iterating over various fields so let’s unroll those loops in advance.

Class Method Summary collapse

Class Method Details

.call_helper(receiver, meth, fields) ⇒ Object 



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# File 'lib/zippo/binary_structure/meta.rb', line 23

def call_helper(receiver, meth, fields)
  "#{receiver}.#{meth}(#{fields_as_args(fields)})"
end

.define_converter_for(klass, meth, other) ⇒ Object 



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# File 'lib/zippo/binary_structure/meta.rb', line 75

def define_converter_for(klass, meth, other)
  # serialize the klass reference "other"
  # we can't just use to_s, since that won't work if the class is anonymous
  class_ref = "ObjectSpace._id2ref(#{other.object_id})"

  common_fields = klass.common_fields_with(other)

  helper_name = "initialize_from_#{object_id}"
  define_helper(other, helper_name, common_fields)

  default_fields = other.structure.fields.select do |field|
    field.options[:default] || field.options[:signature]
  end.reject do |field|
    common_fields.include? field.name
  end

  define_helper(other, "other_fields", default_fields.map(&:name))
  default_values = default_fields.map do |f|
    f.options[:signature] ||
    f.options[:default]
  end

  klass.class_eval """
    def #{meth}
      obj = #{class_ref}.new
      obj.other_fields(#{default_values.map(&:inspect).join(', ')})
      #{call_helper("obj", helper_name, common_fields)}
      obj
    end
  """
end

.define_defaults_method_for(klass) ⇒ Object 



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# File 'lib/zippo/binary_structure/meta.rb', line 27

def define_defaults_method_for(klass)
  buf = []
  buf << "def defaults"
  klass.structure.fields.each do |field|
    buf << %(@#{field.name} = #{field.options[:default].inspect}) if field.options[:default]
    buf << %(@#{field.name} = #{field.options[:signature].inspect}) if field.options[:signature]
  end
  buf << "self"
  buf << "end"
  klass.class_eval buf.join("\n")
end

.define_helper(klass, meth, fields) ⇒ Object

Defines a method on the specified class that sets a bunch of fields at once.



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# File 'lib/zippo/binary_structure/meta.rb', line 9

def define_helper(klass, meth, fields)
  buf = []
  buf << "def #{meth}(#{0.upto(fields.size - 1).map { |x|"a#{x}" }.join(',')})"
  fields.each_with_index do |field, i|
    buf << "@#{field} = a#{i}"
  end
  buf << "end"
  klass.class_eval buf.join("\n")
end

.define_pack_method_for(klass) ⇒ Object 



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# File 'lib/zippo/binary_structure/meta.rb', line 107

def define_pack_method_for(klass)
  fields = klass.structure.fields.map(&:name)
  packing_string = klass.structure.fields.map(&:pack).join('')

  helper_method =
    """
      def fields_for_packing
        [#{fields_as_args(fields)}]
      end
    """
  klass.structure.owner_class.class_eval helper_method

  klass.class_eval do
    define_method :pack do |obj|
      @io << obj.fields_for_packing.pack(packing_string)
    end
  end
end

.define_unpack_method_for(klass) ⇒ Object

XXX - should write a spec for the “multiple helpers” implementation, none of the current binary structures would make use of it, as they all have a bunch of fixed fields, then the variable fields at the end. a test should def self.define_unpack_method



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# File 'lib/zippo/binary_structure/meta.rb', line 44

def define_unpack_method_for(klass)
  buf = "def unpack\n"
  buf << "obj = self.class.structure.owner_class.new\n"
  helper_num = -1 # keep track of the number of helper methods we've created
  field_buf = []
  # iterate over the fields, gathering up the fixed fields in a
  # group. once a variable field is hit, unpack the current group of
  # fixed fields, then use that to read any variable fields. repeat.
  klass.structure.fields.each do |field|
    if field.options[:size]
      # unpack fixed group
      unless field_buf.empty?
        s = field_buf.map(&:width).reduce(&:+)
        buf << %{arr = @io.read(#{s}).unpack("#{field_buf.map(&:pack).join('')}")\n}
        helper_name = "binary_structure_unpack_helper_#{helper_num += 1}"
        define_helper(klass.structure.owner_class, helper_name, field_buf.map(&:name))
        buf << "obj.#{helper_name}(*arr)\n"
      end
      # unpack variable-length field
      buf << %{obj.instance_variable_set :@#{field.name}, @io.read(obj.#{field.options[:size]})\n}
      field_buf = []
    else
      field_buf << field
    end
  end
  buf << "obj\n"
  buf << "end\n"

  klass.class_eval(buf)
end

.fields_as_args(fields) ⇒ Object 



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# File 'lib/zippo/binary_structure/meta.rb', line 19

def fields_as_args(fields)
  fields.map { |f| "@#{f}" }.join(", ")
end