Module: BinData::Int

Defined in:
lib/bindata/int.rb

Overview

Defines a number of classes that contain an integer. The integer is defined by endian, signedness and number of bytes.

Class Method Summary collapse

Class Method Details

.class_name(nbits, endian, signed) ⇒ Object 



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# File 'lib/bindata/int.rb', line 24

def class_name(nbits, endian, signed)
  endian_str = (endian == :big) ? "be" : "le"
  base = (signed == :signed) ? "Int" : "Uint"

  "#{base}#{nbits}#{endian_str}"
end

.create_clamp_code(min, max) ⇒ Object 



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# File 'lib/bindata/int.rb', line 61

def create_clamp_code(min, max)
  "val = (val < #{min}) ? #{min} : (val > #{max}) ? #{max} : val"
end

.create_int2uint_code(nbits) ⇒ Object 



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# File 'lib/bindata/int.rb', line 65

def create_int2uint_code(nbits)
  "val = val & #{(1 << nbits) - 1}"
end

.create_int_methods(int_class, nbits, endian) ⇒ Object 



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# File 'lib/bindata/int.rb', line 44

def create_int_methods(int_class, nbits, endian)
  raise "nbits must be divisible by 8" unless (nbits % 8).zero?

  max = (1 << (nbits - 1)) - 1
  min = -(max + 1)

  clamp = create_clamp_code(min, max)
  read = create_read_code(nbits, endian)
  to_binary_s = create_to_binary_s_code(nbits, endian)

  int2uint = create_int2uint_code(nbits)
  uint2int = create_uint2int_code(nbits)

  define_methods(int_class, nbits / 8, clamp, read, to_binary_s,
                   int2uint, uint2int)
end

.create_read_code(nbits, endian) ⇒ Object 



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# File 'lib/bindata/int.rb', line 76

def create_read_code(nbits, endian)
  # determine "word" size and unpack directive
  if (nbits % 32).zero?
    bytes_per_word = 4
    d = (endian == :big) ? 'N' : 'V'
  elsif (nbits % 16).zero?
    bytes_per_word = 2
    d = (endian == :big) ? 'n' : 'v'
  else
    bytes_per_word = 1
    d = 'C'
  end

  bits_per_word = bytes_per_word * 8
  nwords        = nbits / bits_per_word
  nbytes        = nbits / 8

  idx = (0 ... nwords).to_a
  idx.reverse! if (endian == :big)

  unpack_str = "a = io.readbytes(#{nbytes}).unpack('#{d * nwords}')"

  parts = (0 ... nwords).collect do |i|
            i.zero? ? "a.at(#{idx[i]})" :
                      "(a.at(#{idx[i]}) << #{bits_per_word * i})"
          end
  assemble_str = parts.join(" + ")

  "(#{unpack_str}; #{assemble_str})"
end

.create_to_binary_s_code(nbits, endian) ⇒ Object 



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

def create_to_binary_s_code(nbits, endian)
  # special case 8bit integers for speed
  return "val.chr" if nbits == 8

  # determine "word" size and pack directive
  if (nbits % 32).zero?
    bytes_per_word = 4
    d = (endian == :big) ? 'N' : 'V'
  elsif (nbits % 16).zero?
    bytes_per_word = 2
    d = (endian == :big) ? 'n' : 'v'
  else
    bytes_per_word = 1
    d = 'C'
  end

  bits_per_word = bytes_per_word * 8
  nwords        = nbits / bits_per_word
  mask          = (1 << bits_per_word) - 1

  vals = (0 ... nwords).collect do |i|
           i.zero? ? "val" : "(val >> #{bits_per_word * i})"
         end
  vals.reverse! if (endian == :big)

  parts = (0 ... nwords).collect { |i| "#{vals[i]} & #{mask}" }
  array_str = "[" + parts.join(", ") + "]"

  "#{array_str}.pack('#{d * nwords}')"
end

.create_uint2int_code(nbits) ⇒ Object 



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# File 'lib/bindata/int.rb', line 69

def create_uint2int_code(nbits)
  mask = (1 << (nbits - 1)) - 1

  "val = ((val & #{1 << (nbits - 1)}).zero?) ? " +
           "val & #{mask} : -(((~val) & #{mask}) + 1)"
end

.create_uint_methods(int_class, nbits, endian) ⇒ Object 



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# File 'lib/bindata/int.rb', line 31

def create_uint_methods(int_class, nbits, endian)
  raise "nbits must be divisible by 8" unless (nbits % 8).zero?

  min = 0
  max = (1 << nbits) - 1

  clamp = create_clamp_code(min, max)
  read = create_read_code(nbits, endian)
  to_binary_s = create_to_binary_s_code(nbits, endian)

  define_methods(int_class, nbits / 8, clamp, read, to_binary_s)
end

.define_class(nbits, endian, signed) ⇒ Object 



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

def define_class(nbits, endian, signed)
  name = class_name(nbits, endian, signed)
  return if BinData.const_defined?(name)

  int_type = (signed == :signed) ? 'int' : 'uint'
  creation_method = "create_#{int_type}_methods"

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

.define_methods(int_class, nbytes, clamp, read, to_binary_s, int2uint = nil, uint2int = nil) ⇒ Object 



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# File 'lib/bindata/int.rb', line 138

def define_methods(int_class, nbytes, clamp, read, to_binary_s,
                     int2uint = nil, uint2int = nil)
  int_class.module_eval <<-END
    #---------------
    private

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

    def _do_num_bytes
      #{nbytes}
    end

    def sensible_default
      0
    end

    def value_to_binary_string(val)
      #{clamp}
      #{int2uint unless int2uint.nil?}
      #{to_binary_s}
    end

    def read_and_return_value(io)
      val = #{read}
      #{uint2int unless uint2int.nil?}
    end
  END
end