Module: BinData::BitField

Defined in:
lib/bindata/bits.rb

Overview

Defines a number of classes that contain a bit based integer. The integer is defined by endian and number of bits.

Class Method Summary collapse

Class Method Details

.create_methods(bit_class, nbits, endian) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 20

def self.create_methods(bit_class, nbits, endian)
  min = 0
  max = (1 << nbits) - 1
  clamp = "val = (val < #{min}) ? #{min} : (val > #{max}) ? #{max} : val"

  # allow single bits to be used as booleans
  if nbits == 1
    clamp = "val = (val == true) ? 1 : (not val) ? 0 : #{clamp}"
  end

  define_methods(bit_class, nbits, endian.to_s, clamp)
end

.define_class(nbits, endian) ⇒ Object

:nodoc: all



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# File 'lib/bindata/bits.rb', line 8

def self.define_class(nbits, endian)
  name = "Bit#{nbits}"
  name += "le" if endian == :little

  BinData.module_eval <<-END
    class #{name} < BinData::BasePrimitive
      register(self.name, self)
      BitField.create_methods(self, #{nbits}, :#{endian.to_s})
    end
  END
end

.define_methods(bit_class, nbits, endian, clamp) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 33

def self.define_methods(bit_class, nbits, endian, clamp)
  bit_class.module_eval <<-END
    #---------------
    private

    def _assign(val)
      #{clamp}
      super(val)
    end

    def _do_write(io)
      raise "can't write whilst reading \#{debug_name}" if @in_read
      io.writebits(_value, #{nbits}, :#{endian})
    end

    def _do_num_bytes(ignored)
      #{nbits} / 8.0
    end

    def read_and_return_value(io)
      io.readbits(#{nbits}, :#{endian})
    end

    def sensible_default
      0
    end
  END
end