From: Brian Candler <B.Candler@...>
Date: 2002-10-12T19:44:42+09:00
Subject: Re: Things That Newcomers to Ruby Should Know

On Sat, Oct 12, 2002 at 11:11:47AM +0100, Brian Candler wrote:
> However in practise this is efficient, since there appears to be a very
> compact internal representation of references to Fixnums:
> 
> irb(main):001:0> 0.id
> 1
> irb(main):002:0> 1.id
> 3
> irb(main):003:0> 2.id
> 5

... which I presume is cleverly exploiting the property that in the
underlying processor, all pointers need to point to objects which are
word-aligned; a word is 16 bits (2 bytes) or a multiple thereof; and
therefore all valid pointers are even.

So if an odd pointer cannot be valid, we might as well use it to represent a
Fixnum, with the value in the top 31 bits.

Brian.