From: Dominik Bathon <dbatml@...>
Date: 2005-07-02T10:27:59+09:00
Subject: Re: How and where Fixnum are created

On Sat, 02 Jul 2005 02:32:38 +0200, Daniel Brockman <daniel@brockman.se>  
wrote:

> Okay, I realize that this explanation turned out pretty confusing.
> For more information, you might search for ``ruby immediate values.''
>
> I hope this helps at least a bit,

If you look at ruby.h, you will find the following defines:

#define FIXNUM_MAX (LONG_MAX>>1)
#define FIXNUM_MIN RSHIFT((long)LONG_MIN,1)

#define FIXNUM_FLAG 0x01
#define INT2FIX(i) ((VALUE)(((long)(i))<<1 | FIXNUM_FLAG))
#define LONG2FIX(i) INT2FIX(i)

...

#define FIX2LONG(x) RSHIFT((long)x,1)
#define FIX2ULONG(x) (((unsigned long)(x))>>1)
#define FIXNUM_P(f) (((long)(f))&FIXNUM_FLAG)
#define POSFIXABLE(f) ((f) <= FIXNUM_MAX)
#define NEGFIXABLE(f) ((f) >= FIXNUM_MIN)
#define FIXABLE(f) (POSFIXABLE(f) && NEGFIXABLE(f))


They should be self-explanatory after Daniel's nice explanation, and  
should clear it up further.

You can also see how it works if you look at the object_id of Fixnums:

>> 1.object_id
=> 3
>> 42.object_id
=> 85
>> ObjectSpace._id2ref(87)
=> 43
>> ObjectSpace._id2ref(-87)
=> -44
>> ObjectSpace._id2ref(-86)
RangeError: 0xffffffaa is not id value
         from (irb):5:in `_id2ref'
         from (irb):5


Dominik