Re: [PATCH] Add `fixnum?' VM primitive

[Andreas Rottmann]

address@hidden (Ludovic Courtès) writes:

> Hello!
>
> Andreas Rottmann <address@hidden> writes:
>
>> address@hidden (Ludovic Courtès) writes:
>>
>>> Hi!
>>>
>>> Andreas Rottmann <address@hidden> writes:
>>>
>>>> +SCM_DEFINE (scm_fixnum_p, "fixnum?", 1, 0, 0,
>>>> +            (SCM x),
>>>> +            "Return @code{#t} if @var{x} is a fixnum, @code{#f} 
>>>> otherwise.")
>>>> +#define FUNC_NAME s_scm_fixnum_p
>>>> +{
>>>> +  return scm_from_bool (SCM_I_INUMP (x));
>>>> +}
>>>> +#undef FUNC_NAME
>>>
>>> For 2.0 I think you could go with this wonderful hack:
>>>
>>>   (define (fixnum? x)
>>>     (not (= 0 (logand 2 (object-address x)))))
>>>
>>> (An inlinable variant thereof, as done in srfi-9.scm.)
>>>
>> Excellent.  Should we put `define-inlinable' in some common place to
>> avoid code duplication?  If so, where?
>
> That would be nice, if we are confident that it’s not broken any more. ;-)
> ISTR that Chez’ ‘define-integrable’ macro is hairier than that, so I
> wonder if our implementation is too naive.  Thoughts?
>
I'll have another look at that; if it turns out it's good, would `(ice-9
inline)' be a proper place for it?

>>> For ‘master’ your patch looks good to me modulo a few details.  Why did
>>> you need to renumber VM opcodes? 
>>>
>> I didn't need to do so, but the neat order elicited my instinct to keep
>> it ;-).  I'll revert that part; should I then put `fixnum?' at the end?
>
> Yes please.
>
> I guess we could even add the new opcode in stable-2.0 because Andy
> tweaked objcode version check to be smarter—i.e., 2.0.1 would be able to
> read objcodes produced by either 2.0.1 or 2.0.0.
>
> WDYT?
>
That would be nice indeed.

>>> Also, I’d prefer not to have ‘fixnum?’ in the default name space
>>> because:
>>>
>>>   1. In Guile parlance, it’d rather be ‘immediate-number?’ (info
>>>      "(guile) Immediate objects").
>>>
>>>   2. I think this fixnum thing is a breach in the numerical tower.
>>>
>> I'm fine with moving it out of the default namespace (I was actually
>> worried about that, too).  However, I vaguely remember the compiler not
>> outputting the opcode when I did not define `fixnum?' as a C-based
>> procedure in the default namespace, but I might be mistaken.  I would
>> appreciate pointer(s) of where to look to learn about how the compiler
>> decides if some procedure can be emitted as an opcode (but I think I
>> would be able to figure that out myself, but pointers would be nice
>> nevertheless ;-)).
>
> In (language tree-il primitives), there’s ‘add-interesting-primitive!’,
> which checks whether the primitive name is bound in the current module.
>
OK, I'll experiment with that.

> BTW why does the ZIP implementation in Industria keep calling ‘fixnum?’?
>
It's actually the implementation of `(rnrs arithmetic fixnums)' that
calls fixnum for almost every operation; also see my other mail [0],
where I talk about lifting that at least for some operations.

[0] http://lists.gnu.org/archive/html/guile-devel/2011-03/msg00235.html

Regards, Rotty
-- 
Andreas Rottmann -- <http://rotty.yi.org/>