Rotate Bits Right operation in Ruby

Question

Is there a Rotate Bits Right in Ruby ?

Or how can I do that please.

Thanks

Answer 1

Some facts:

• Ruby has operators << and >> to shift, but no built-in rotate operator. You have to fake it.
• Ruby's Fixnum class automatically promotes to Bignum when the value exceeds the machine word size. This includes numbers that would fit in an unsigned word but not a signed word -- for example, 0xffffffff is a positive Bignum, not a negative Fixnum.

So if you want a rotate operation, you a) have to write it using the shift operators, b) either hardcode 32 or 64 bits or ask Fixnum for the word size, and c) accept that the result might end up being a Bignum.

That being said, this might work:

class Integer
  def ror count
    (self >> count) | (self << (32 - count)) & 0xFFFFFFFF
  end
end

>> printf "0x%x\n", (0x01234567.ror 4)
0x70123456

Answer 2

If you need higher performance, and don't mind adding a dependency, there is the bit-twiddle gem, which provides this operation implemented in native code:

require 'bit-twiddle/core_ext'
# rotate by 8 bits
0x08048586.rrot32(8).to_s(16) # => "86080485"

Disclosure: I'm the author of this gem.