From: Nicolas Cannasse <ncannasse@motion-twin.com>
To: Brian Hurt <bhurt@spnz.org>
Cc: "Michael D. Adams" <mdmkolbe@gmail.com>, caml-list@inria.fr
Subject: Re: [Caml-list] Efficency of varient types
Date: Sun, 27 Nov 2005 11:02:51 +0100 [thread overview]
Message-ID: <4389844B.90008@motion-twin.com> (raw)
In-Reply-To: <Pine.LNX.4.63.0511262336031.24132@localhost.localdomain>
Brian Hurt wrote:
>
>
> On Sun, 27 Nov 2005, Michael D. Adams wrote:
>
>> I agree, which is why it was my hope that OCaml might do some of that
>> for me. Consider a home brew bool type, "type mybool = Mytrue |
>> Myfalse". If the compiler were smart enough, it could represent that
>> as an unboxed type.
>
>
> The compiler is smart enough to do that already- variants without
> associated data are represented as ints.
Exactly.
So actually the custom bool can be "safely" casted to the corresponding
real bool since they have same runtime representation.
>> From there it might be a small step to
>> semi-unboxed types such as the one I started this discussion with,
>> "type value = Int of int | Bool of bool | String of string".
>
>
> The problem here is that the variants take two words- one word which
> says which variant it is, and the second word which is the unboxed int,
> unboxed bool, or pointer to the boxed string.
It's a bit more complex.
A variant have a header storing :
- it's tag
- some GC bits
- it's size (number of fields)
Then the data is followed by N fields which are the variant parameters.
That's why there is a semantical difference between
Tag of int * int
and
Tag of (int * int)
In the first case it's a 2 fields block, in the second it's a on-field
block storing a 2 fields tuple.
I think that the compiler is pretty good at unboxing floats and maybe
int32 when doing some numerical calculus. Other optimizations are more
tricky.
Nicolas
next prev parent reply other threads:[~2005-11-27 9:53 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-25 23:53 Michael D. Adams
2005-11-26 0:31 ` [Caml-list] " Nicolas Cannasse
2005-11-26 1:22 ` Brian Hurt
2005-11-26 9:39 ` Nicolas Cannasse
2005-11-28 0:17 ` Obj or not Obj Christophe Raffalli
2005-11-28 8:41 ` [Caml-list] " Nicolas Cannasse
2005-11-28 9:27 ` Christophe Raffalli
2005-11-28 9:33 ` skaller
2005-11-28 8:43 ` Alain Frisch
2005-11-26 2:54 ` [Caml-list] Efficency of varient types skaller
2005-11-27 5:06 ` Michael D. Adams
2005-11-27 5:45 ` Brian Hurt
2005-11-27 10:02 ` Nicolas Cannasse [this message]
2005-11-27 15:35 ` Michael D. Adams
2005-11-27 18:08 ` Brian Hurt
2005-12-02 15:07 ` Michael D. Adams
2005-11-26 1:18 ` Jon Harrop
2005-11-27 14:57 ` Lukasz Stafiniak
2005-11-27 15:47 ` Lukasz Stafiniak
2005-11-28 8:14 ` Christophe Raffalli
2005-11-28 7:24 ` David Baelde
2005-11-28 7:49 ` Jacques Garrigue
2005-11-28 10:01 ` Jon Harrop
2005-11-28 10:26 ` Luc Maranget
2005-11-28 7:53 ` Ville-Pertti Keinonen
2005-12-01 17:05 ` Stefan Monnier
2005-12-02 15:07 ` [Caml-list] " Michael D. Adams
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