From: Eric Hodel <drbrain@...7.net>
Date: 2005-05-05T06:32:02+09:00
Subject: Re: Fixnum's binary representation

On 04 May 2005, at 09:04, camsight@gmail.com wrote:

> Hi, people!
>
> As far as I know, Ruby's Fixnum is 30-bit signed integer.
> One bit is used as a flag for whether it's a direct value.
> Another bit is used for non-Fixnum direct values.
>
> My guess is that Fixnum#[] works as if it's 32-bit signed integer.
> It's not showing its real binary representation.
> Is my guess true?

$ ruby
puts (-10..10).map { |i| "#{i}: #{i.object_id}" }.join("\n")
-5: -9
-4: -7
-3: -5
-2: -3
-1: -1
0: 1
1: 3
2: 5
3: 7
4: 9
5: 11

A Fixnum's object_id is 2N+1 its value, so if you want a Fixnum's 
binary representation, use its object_id.  (So long as the object_id is 
a Fixnum.)

#define FIXNUM_FLAG 0x01
#define INT2FIX(i) ((VALUE)(((long)(i))<<1 | FIXNUM_FLAG))

Also, a Fixnum always has an odd object_id, while any other VALUE has 
an even object_id.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
FEC2 57F1 D465 EB15 5D6E  7C11 332A 551C 796C 9F04