From: Makoto Inada <mak@...>
Date: 2007-04-14T02:32:47+09:00
Subject: Re: Question about Fixnum

------=_Part_18571_18641997.1176485564731
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

Because a bit is used to differentiate fixnums from other value types
appearing in the same context, such as object pointers.

A regular Ruby object has its own memory space which Ruby interpreter has
access via a pointer.
Allocating memory for each number is obviously too expensive, so Matz
decided to store "small" numbers in a pointer itself.  This is Fixnum.  This
means you have to distinguish a fixnum from a pointer somehow.  The bit I
mentioned is used for the purpose.  LSB of a fixnum is set to 1 because an
object pointer's LSB is guaranteed to be 0 on a 32bit/64bit system.

-Mak

On 4/13/07, huang zhimin <flyerhzm@gmail.com > wrote:
>
> On 4/14/07, huang zhimin < flyerhzm@gmail.com> wrote:
> >
> > Why the range of Fixnum is -2^30 ~ 2^30 rather than -2^31 ~2^31 ?
>
>                                                        ~~~~should be
> 2^30-1  ~~~~2^31-1
>
>
> --
> > flyerhzm@hotmail.com
>
>
>
>
> --
> flyerhzm@hotmail.com
>

------=_Part_18571_18641997.1176485564731--