From: Judson Lester <nyarly@...>
Date: 2008-01-26T07:03:12+09:00
Subject: Re: Circular shift

On Jan 25, 2008 1:47 PM, Mental Guy <mental@rydia.net> wrote:
> Since you showed interest, though, I'll continue with what I would
> have eventually gotten to:  if the register width is a power of two,
> you can do some additional tricks.

Let's just say I share your love for binary arithmetic.  But, hey, I'm
more than happy to play straight man for a good punchline.

> Now, if we decide to hard-code a specific register width, we
> can simplify things pretty dramatically (let's pick 8, which
> is 2 ** 3):
>

Say, that almost sounds like a use case for a class.  Something like

class Register < Integer
  def initialize(width, value);
    ...
  end
end

(or even
def Register(width)
  klass = class.new(Register)
  #metaprogrammy stuff to define klass::width
end)

But that would be drifting from the topic.

> ---
>
> [1] Be careful when porting code to other languages; they may differ
> in their treatment of negative numbers with the modulo operator, and
> in C its behavior is platform-dependent.  Ruby's way is the best way
> for modular arithmetic though.

Yeah, no kidding.  C (and many related languages) also fix the width
of numeric types and have built-in (<<<) circular shifts.

Judson
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