[Caml-list] what magic is this?

[Caml-list] what magic is this?

[effbiae]

i've started writing a mmap module.  i'm looking at the source to bigarray
to see how it's done. in bigarray.ml, external functions
 Array1.{get,set} are linked to "%bigarray_{ref,set}_1"

1) what's the % -- is this what allows the fast access to the base data?
2) bigarray_ref_1 and bigarray_set_1 are not defined anywhere

hold on... greps...finds...

  bytecomp/translcore.ml:   primitives_table ... "%bigarray_ref_1" ...

aahhh.

i bet i could reuse this in my mmap module.  the question is how?

typedef struct _MM{int fd;void *map;unsigned long size;}*MM;

module Mm = struct
 type ('a,'b)t
 external create: 'a a -> 'b b -> ('a, 'b) t
 external get: ('a, 'b) t -> int -> 'a = "%bigarray_ref_1"
 external set: ('a, 'b) t -> int -> 'a -> unit = "%bigarray_set_1"
...end

any pointers greatly appreciated.


jack

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Re: [Caml-list] what magic is this?

[David Monniaux]

On Wed, 4 Aug 2004 effbiae@ivorykite.com wrote:

> i've started writing a mmap module.  i'm looking at the source to bigarray
> to see how it's done. in bigarray.ml, external functions
>  Array1.{get,set} are linked to "%bigarray_{ref,set}_1"

External functions starting with a % are primitives that are
directly compiled by the ocamlopt compiler into specific code, without the
overhead of a function call.

David Monniaux            http://www.di.ens.fr/~monniaux
Laboratoire d'informatique de l'École Normale Supérieure,
Paris, France

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Re: [Caml-list] what magic is this?

[Jack Andrews]

> External functions starting with a % are primitives that are
> directly compiled by the ocamlopt compiler into specific code,
> without the overhead of a function call.

oooh - nice.

now a request.  it would be *really* nice if there were some public
%primitives that could be used by the FFI user.

i'm thinking they would be similar to the bigarray_ref/set primitives, but
would publish a contract for the lib writer.

this would be something to set ocaml apart (not that it isn't set apart
already)  a fast FFI is something that languages lack - i wrote a
benchmark for java's JNI that demonstrated the problem of needing to
optimise the loop  while(next())set(get());  (google for jni benchmark).

i'd propose that:
  - in the C code, the first member of a custom struct is a pointer
      eg:  struct CUST
           {  void *ptr;
              int   size;
           };

  - values are allocated as usual:
     value vcust=alloc_custom(&ops,sizeof(struct CUST),x,y);

  - four new primitives are available for use in ml file:
      external   get_int : <cust_type> -> int -> int   = "%ffi_get_int"
      external get_float : <cust_type> -> int -> float = "%ffi_get_float"
      external   set_int : <cust_type> -> int -> int -> unit =
                                                         "%ffi_set_int"
      external set_float : <cust_type> -> int -> float -> unit =
                                                         "%ffi_set_float"

it would take me a week to work out how to implement these primitives, but
one of you ocaml guys could do it a lot quicker.  please?  you'd only have
to re-write it after i made a complete bodge of it :)

thanks in advance,


jack.

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