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_clamp_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 87

def create_clamp_code(nbits, signed)
  if nbits == :nbits
    create_dynamic_clamp_code(nbits, signed)
  else
    create_fixed_clamp_code(nbits, signed)
  end
end

.create_do_num_bytes_code(nbits) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 79

def create_do_num_bytes_code(nbits)
  if nbits == :nbits
    "nbits / 8.0"
  else
    nbits / 8.0
  end
end

.create_dynamic_clamp_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 95

def create_dynamic_clamp_code(nbits, signed)
  if signed == :signed
    max = "max = (1 << (nbits - 1)) - 1"
    min = "min = -(max + 1)"
  else
    max = "max = (1 << nbits) - 1"
    min = "min = 0"
  end

  "#{max}; #{min}; val = (val < min) ? min : (val > max) ? max : val"
end

.create_fixed_clamp_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 107

def create_fixed_clamp_code(nbits, signed)
  if nbits == 1 and signed == :signed
    raise "signed bitfield must have more than one bit" 
  end

  if signed == :signed
    max = (1 << (nbits - 1)) - 1
    min = -(max + 1)
  else
    min = 0
    max = (1 << nbits) - 1
  end

  clamp = "(val < #{min}) ? #{min} : (val > #{max}) ? #{max} : val"

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

  "val = #{clamp}"
end

.create_int2uint_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 130

def create_int2uint_code(nbits, signed)
  if signed != :signed
    ""
  elsif nbits == :nbits
    "val &= (1 << nbits) - 1"
  else
    "val &= #{(1 << nbits) - 1}"
  end
end

.create_nbits_code(nbits) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 71

def create_nbits_code(nbits)
  if nbits == :nbits
    "nbits = eval_parameter(:nbits)"
  else
    ""
  end
end

.create_params_code(nbits) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 63

def create_params_code(nbits)
  if nbits == :nbits
    "mandatory_parameter :nbits"
  else
    ""
  end
end

.create_uint2int_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 140

def create_uint2int_code(nbits, signed)
  if signed != :signed
    ""
  elsif nbits == :nbits
    "val -= (1 << nbits) if (val >= (1 << (nbits - 1)))"
  else
    "val -= #{1 << nbits} if (val >= #{1 << (nbits - 1)})"
  end
end

.define_class(name, nbits, endian, signed = :unsigned) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 9

def define_class(name, nbits, endian, signed = :unsigned)
  unless BinData.const_defined?(name)
    BinData.module_eval <<-END
      class #{name} < BinData::BasePrimitive
        BitField.define_methods(self, #{nbits.inspect}, #{endian.inspect}, #{signed.inspect})
      end
    END
  end

  BinData.const_get(name)
end

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



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# File 'lib/bindata/bits.rb', line 21

def define_methods(bit_class, nbits, endian, signed)
  bit_class.module_eval <<-END
    #{create_params_code(nbits)}

    def assign(val)
      #{create_nbits_code(nbits)}
      #{create_clamp_code(nbits, signed)}
      super(val)
    end

    def do_write(io)
      #{create_nbits_code(nbits)}
      val = _value
      #{create_int2uint_code(nbits, signed)}
      io.writebits(val, #{nbits}, :#{endian})
    end

    def do_num_bytes
      #{create_nbits_code(nbits)}
      #{create_do_num_bytes_code(nbits)}
    end

    def bit_aligned?
      true
    end

    #---------------
    private

    def read_and_return_value(io)
      #{create_nbits_code(nbits)}
      val = io.readbits(#{nbits}, :#{endian})
      #{create_uint2int_code(nbits, signed)}
      val
    end

    def sensible_default
      0
    end
  END
end