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.

Constant Summary collapse

@@mutex =

:nodoc: all

Mutex.new

Class Method Summary collapse

Class Method Details

.create_clamp_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 86

def create_clamp_code(nbits, signed)
  if nbits == :nbits
    create_dynamic_clamp_code(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 78

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

.create_dynamic_clamp_code(signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 94

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

  "val = val.clamp(#{min}, #{max})"
end

.create_fixed_clamp_code(nbits, signed) ⇒ Object 



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# File 'lib/bindata/bits.rb', line 106

def create_fixed_clamp_code(nbits, signed)
  if nbits == 1 && 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 = val.clamp(#{min}, #{max}))"

  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 129

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 70

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 62

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 139

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 12

def define_class(name, nbits, endian, signed = :unsigned)
  @@mutex.synchronize do
    unless BinData.const_defined?(name)
      BinData.module_eval <<-END
        class #{name} < BasePrimitive
          #{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
    end
  end

  BinData.const_get(name)
end