From: Brian Candler <B.Candler@...>
Date: 2005-06-04T23:29:35+09:00
Subject: Converting variable-length binary value

I'm sure there ought to be a Ruby function to do this, but I've been
scratching my head whilst going through the Pickaxe book :-)

I want to encode/decode a positive number to/from a variable-length
big-endian binary string.

Originally the best I could come up with was:

  str = "\001\002\003"
  val = 0
  str.each_byte { |b| val = (val << 8) | b }
  p val
  # => 66051

  val = 1234
  str = ""
  while (val > 0)
    str = (val & 0xff).chr + str
    val >>= 8
  end
  p str
  # => "\004\322"

pack/unpack seem only to work for fixed lengths, e.g. 2 or 4 bytes.

Is there a faster or simpler way of doing this in Ruby?

Then I discovered I can go via hex:

  p "\001\002\003".unpack("H*")[0].hex
  # => 66051

  str = 1234.to_s(16)
  str = "0#{str}" if str.length % 2 != 0
  val = [str].pack("H*")
  p val
  # => "\004\322"

That's still pretty nasty. Any better offers?

Thanks,

Brian.