module Net::BER::Extensions::Integer

BER extensions to the Integer class, affecting Fixnum and Bignum objects.

Public Instance Methods

to_ber() click to toggle source

Converts the Integer to BER format.

# File lib/net/ber/core_ext/integer.rb, line 6
def to_ber
  "\002#{to_ber_internal}"
end
to_ber_application(tag) click to toggle source

Generate a BER-encoding for an application-defined INTEGER. Examples of such integers are SNMP’s Counter, Gauge, and TimeTick types.

# File lib/net/ber/core_ext/integer.rb, line 30
def to_ber_application(tag)
  [0x40 + tag].pack("C") + to_ber_internal
end
to_ber_enumerated() click to toggle source

Converts the Integer to BER enumerated format.

# File lib/net/ber/core_ext/integer.rb, line 12
def to_ber_enumerated
  "\012#{to_ber_internal}"
end
to_ber_length_encoding() click to toggle source

Converts the Integer to BER length encoding format.

# File lib/net/ber/core_ext/integer.rb, line 18
def to_ber_length_encoding
  if self <= 127
    [self].pack('C')
  else
    i = [self].pack('N').sub(/^[\0]+/, "")
    [0x80 + i.length].pack('C') + i
  end
end

Private Instance Methods

to_ber_internal() click to toggle source

Used to BER-encode the length and content bytes of an Integer. Callers must prepend the tag byte for the contained value.

# File lib/net/ber/core_ext/integer.rb, line 37
def to_ber_internal
  # Compute the byte length, accounting for negative values requiring two's
  # complement.
  size  = 1
  size += 1 until (((self < 0) ? ~self : self) >> (size * 8)).zero?

  # Padding for positive, negative values. See section 8.5 of ITU-T X.690:
  # http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf

  # For positive integers, if most significant bit in an octet is set to one,
  # pad the result (otherwise it's decoded as a negative value).
  if self > 0 && (self & (0x80 << (size - 1) * 8)) > 0
    size += 1
  end

  # And for negative integers, pad if the most significant bit in the octet
  # is not set to one (othwerise, it's decoded as positive value).
  if self < 0 && (self & (0x80 << (size - 1) * 8)) == 0
    size += 1
  end

  # Store the size of the Integer in the result
  result = [size]

  # Appends bytes to result, starting with higher orders first. Extraction
  # of bytes is done by right shifting the original Integer by an amount
  # and then masking that with 0xff.
  while size > 0
    # right shift size - 1 bytes, mask with 0xff
    result << ((self >> ((size - 1) * 8)) & 0xff)
    size -= 1
  end

  result.pack('C*')
end