Binding to C

Binding to C

[chris]

Hi,

I came across the following in libjpeg... what should I map it to?

const char* const* jpeg_message_table

Also does anyone have any advice in general mapping to C.  For the 
jpeg_error_mgr struct, I mapped ptrs to functions to System.Address and 
made the struct a record.  Will this work, or will the corresponding 
type of the struct have to be a System.Address?


Chris

package Low_Jpg.Error is

    package C renames Interfaces.C;

    type Jpeg_Error_Mgr is record
       Error_Exit      : System.Address; -- addr of a handler
       Emit_Message    : System.Address;
       Output_Message  : System.Address;
       Format_Message  : System.Address;
       Reset_Error_Mgr : System.Address;
       Msg_Code        : C.Int;
       Msg_Parm        : System.Address;
       Trace_Level     : C.Int;
       Num_Warnings    : C.Long;
    end record;
    pragma Convention (C, Jpeg_Error_Mgr);

end Low_Jpg.Error;

Re: Binding to C

[Martin Krischik]

chris wrote:

> Hi,
> 
> I came across the following in libjpeg... what should I map it to?
> 
> const char* const* jpeg_message_table

const works to the left unless it comes first. So:

(const char) (* const)* jpeg_message_table

Try:

type jpeg_message is access constant character;
type jpeg_message_table is access constant jpeg_message;

> 

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com

Re: Binding to C

[tmoran]

>Also does anyone have any advice in general mapping to C.
 Look at some of the Windows binding source code at www.adapower.com
>For the jpeg_error_mgr struct, I mapped ptrs to functions to System.Address
>and made the struct a record.  Will this work, or will the corresponding
>type of the struct have to be a System.Address?
 You almost never need a System.Address.  Use access types.

>   type Jpeg_Error_Mgr is record
>      Error_Exit      : System.Address; -- addr of a handler
>      Emit_Message    : System.Address;
> ...
 Instead:

  type Error_Exit_Ptr is access
  procedure (cinfo   : access Decompress_Cinfo_Type);
  pragma Convention(C, Error_Exit_Ptr);

  type Emit_Message_Ptr is access
  procedure (cinfo    : access Decompress_Cinfo_Type;
             msg_level: Interfaces.C.Int);
  pragma Convention(C, Emit_Message_Ptr);
  ...

  procedure error_exit(cinfo   : access Decompress_Cinfo_Type);
  pragma Export(C, error_exit);

  procedure emit_message(cinfo    : access Decompress_Cinfo_Type;
                         msg_level: Interfaces.C.Int);
  pragma Export(C, Emit_Message);
  ...

  type Jpeg_Error_Mgr is record
    P_Error_Exit: Error_Exit_Ptr;     -- will be set := error_exit'access;
    P_Emit_Message: Emit_Message_Ptr; -- will be set := emit_message'access;
etc.

Re: Binding to C

[chris]

tmoran@acm.org wrote:
>>Also does anyone have any advice in general mapping to C.
> 
>  Look at some of the Windows binding source code at www.adapower.com
> 
>>For the jpeg_error_mgr struct, I mapped ptrs to functions to System.Address
>>and made the struct a record.  Will this work, or will the corresponding
>>type of the struct have to be a System.Address?
> 
>  You almost never need a System.Address.  Use access types.

Thanks, I've converted the small amount done so far to use access types. 
  What about unions?  I don't really care what's in the union, it's 
under the control of the lib, should I put a char_array of size 
JMSG_STR_PARM_MAX in there?


struct jpeg_error_msg {

   ...

   union {
     int i[8];
     char s[JMSG_STR_PARM_MAX];
   } msg_parm;
}

chris
--
to reply change 'spamoff' to 'chris'

Re: Binding to C

[chris]

Martin Krischik wrote:
> chris wrote:
> 
> 
>>Hi,
>>
>>I came across the following in libjpeg... what should I map it to?
>>
>>const char* const* jpeg_message_table
> 
> 
> const works to the left unless it comes first. So:
> 
> (const char) (* const)* jpeg_message_table

Yuck!  I thought it was

(const char *) (const *) jpeg_message_table;

which is (iirc)

type jpeg_message_table is access constant CStrings.chars_ptr;


I hate C!

Re: Binding to C

[Martin Krischik]

chris wrote:

> Martin Krischik wrote:
>> chris wrote:
>> 
>> 
>>>Hi,
>>>
>>>I came across the following in libjpeg... what should I map it to?
>>>
>>>const char* const* jpeg_message_table
>> 
>> 
>> const works to the left unless it comes first. So:
>> 
>> (const char) (* const)* jpeg_message_table
> 
> Yuck!  I thought it was
> 
> (const char *) (const *) jpeg_message_table;

The difference is only that the last * is not constant. But for a parameter
to a function this makes no difference to the user of the function.

> which is (iirc)
> 
> type jpeg_message_table is access constant CStrings.chars_ptr;
 
> I hate C!

Met too.

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com

Re: Binding to C

[Matthew Heaney]

"chris" <spamoff.danx@ntlworld.com> wrote in message
news:MxXSa.2290$l63.28380@newsfep4-glfd.server.ntli.net...
>
> I came across the following in libjpeg... what should I map it to?
>
> const char* const* jpeg_message_table

This is a pointer to a constant array, comprising pointers to constant
strings.

You could use the types in Interfaces.C.*.  Here's another way to do it:

type char_array is array (Natural) of aliased Character;
pragma Convention (C, char_array);
pragma Suppress (Index_Check, On => char_array);

type const_char_ptr is access constant char_array;
for const_char'Storage_Size use 0;
pragma Convention (C, const_char_ptr);

type string_array is array (Natural) of aliased const_char_ptr;
pragma Convention (C, string_array);
pragma Suppress (Index_Check, On => string_array);

type const_string_ptr is access constant string_array;
for const_string_ptr'Storage_Size use 0;
pragma Convention (C, const_string_ptr);

JPEG_Message_Table : const_string_ptr;  -- voila!

-Matt

Re: Binding to C

[Matthew Heaney]

"Martin Krischik" <krischik@users.sourceforge.net> wrote in message
news:13934627.ulbWRIerNL@linux1.krischik.com...
>
> Try:
>
> type jpeg_message is access constant character;
> type jpeg_message_table is access constant jpeg_message;

This is not a very useful binding, as a message table is an array of
strings.  I showed the correct binding in my previous post.

Re: Binding to C

[Matthew Heaney]

"chris" <spamoff.danx@ntlworld.com> wrote in message
news:f3fTa.342$xe6.5412@newsfep4-glfd.server.ntli.net...
> Martin Krischik wrote:
>
> type jpeg_message_table is access constant CStrings.chars_ptr;

Not quite:

type string_array is array (Natural) of aliased CStrings.chars_ptr;
pragma Convention (C, string_array);

type Table_Type is access constant string_array;
pragma Convention (C, Table_Type);
for Table_Type'Storage_Size use 0;

JPEG_Message_Table : Table_Type;

Re: Binding to C

[Freejack]

On Mon, 21 Jul 2003 14:59:30 -0400, chris wrote:

> Hi,
> 
> I came across the following in libjpeg... what should I map it to?
> 
> const char* const* jpeg_message_table
> 
> Also does anyone have any advice in general mapping to C.  For the
> jpeg_error_mgr struct, I mapped ptrs to functions to System.Address and
> made the struct a record.  Will this work, or will the corresponding
> type of the struct have to be a System.Address?

I'd like to add a question...

Has anyone done any sort of specific tutorial on Interfaces.C or
interfacing with C from Ada in general.

This seems to be a question that get's asked a lot in this newsgroup. I
know I could use some good helper docs (along with the LRM) on this
particular subject.

I'm currently trying to create a thin binding to the SleepyCat Berkely DB
library, and I'm spending most of my time looking at other bindings to
figure out what goes where.
Some of the bindings are very good, but it is a bit frustrating at times.

NiCad

Re: Binding to C

[chris]

Freejack wrote:

> I'd like to add a question...
> 
> Has anyone done any sort of specific tutorial on Interfaces.C or
> interfacing with C from Ada in general.

I looked at the Big book of Ada Linux Programming which has binding 
stuff in it, but it's not an indepth tutorial.  There's also some stuff 
in The Lovelace Tutorial iirc.

Re: Binding to C

[Patrice Freydiere]

Chris, if you are looking for building a complete full Jpeg binding, 
your can browse the AGP project (ada game programming)
it contains a jpeg binding, and a PNG binding.

so it can gives you some ideas for C binding from ADA.

hope this help.
Patrice

ps: when i started writing the simplejpeglib binding for ADA.
i had a lot of interfacing problems du to the portability macros of the
jpeglib. (it's surely possible, but when i've started my binding, my C
interfacing Skills from ADA was poor).
So i decided in my design to build a simple C interface to make Ada
binding easier. This permit me to be "C structure independent" and provide a
more easy upgrade of the jpeglib.


On Mon, 21 Jul 2003 20:59:30 +0200, chris wrote:

> Hi,
> 
> I came across the following in libjpeg... what should I map it to?
> 
> const char* const* jpeg_message_table
> 
> Also does anyone have any advice in general mapping to C.  For the 
> jpeg_error_mgr struct, I mapped ptrs to functions to System.Address and 
> made the struct a record.  Will this work, or will the corresponding 
> type of the struct have to be a System.Address?
> 
> 
> Chris
> 
> package Low_Jpg.Error is
> 
>     package C renames Interfaces.C;
> 
>     type Jpeg_Error_Mgr is record
>        Error_Exit      : System.Address; -- addr of a handler
>        Emit_Message    : System.Address;
>        Output_Message  : System.Address;
>        Format_Message  : System.Address;
>        Reset_Error_Mgr : System.Address;
>        Msg_Code        : C.Int;
>        Msg_Parm        : System.Address;
>        Trace_Level     : C.Int;
>        Num_Warnings    : C.Long;
>     end record;
>     pragma Convention (C, Jpeg_Error_Mgr);
> 
> end Low_Jpg.Error;

Re: Binding to C

[Jeffrey Creem]

"Patrice Freydiere" <frett27@free.fr> wrote in message
news:pan.2003.08.09.11.28.57.794916@free.fr...
>
> Chris, if you are looking for building a complete full Jpeg binding,
> your can browse the AGP project (ada game programming)
> it contains a jpeg binding, and a PNG binding.
>

How about a link?? AGP is hardly a unique search term.

Re: Binding to C

[Patrice Freydiere]

Jeffrey, 
i havn't found a web site for Agp , the only link i have is this 

http://www.gnuada.org/alt.html

you'll find a Href to the sources.

Patrice

#
# The Ada Game Package (AGP). The package agp95_v0.1_x11.tar.gz (1719 kB) is targeted for XFree86, the package  agp95_v0.1_fb.tar.gz (1719 kB)  for the GNU/Linux framebuffer console. There is also a partial binding to the Linux framebuffer console (17 kB). These packages compile with gnat-3.11p. If you want to use gnat-3.12p, you have to download this fix package.The software is GPLed, the authors are Wesley Y. Pan and Weston T. Pan.


On Sat, 09 Aug 2003 13:09:21 +0000, Jeffrey Creem wrote:

> 
> "Patrice Freydiere" <frett27@free.fr> wrote in message
> news:pan.2003.08.09.11.28.57.794916@free.fr...
>>
>> Chris, if you are looking for building a complete full Jpeg binding,
>> your can browse the AGP project (ada game programming)
>> it contains a jpeg binding, and a PNG binding.
>>
> 
> How about a link?? AGP is hardly a unique search term.

Re: Binding to C

[chris]

Patrice Freydiere wrote:

> so it can gives you some ideas for C binding from ADA.

Thanks.


> ps: when i started writing the simplejpeglib binding for ADA.
> i had a lot of interfacing problems du to the portability macros of the
> jpeglib. (it's surely possible, but when i've started my binding, my C
> interfacing Skills from ADA was poor).
> So i decided in my design to build a simple C interface to make Ada
> binding easier. This permit me to be "C structure independent" and provide a
> more easy upgrade of the jpeglib.

This is a problem... and I haven't found a *convienant* way to solve 
this (other than wrapping it up as you and Warren pointed out - thanks). 
  Macros change this, that and the other.  My ada code would need to be 
changed at the spec level on different platforms, compilers, etc... 
yuck.  A more experienced Ada developer could probably organise it 
better, but

All I really want to do now is *decode* and encode (at various 
qualities) a jpeg (in RBG).  Later things might get more complicated, 
but for now that's it.  I'm going to look at your lib again now I've got 
a bit more time.

Re: Binding to C

[Patrice Freydiere]

On Tue, 12 Aug 2003 00:49:20 +0100, chris wrote:

> Patrice Freydiere wrote:
> 
>> so it can gives you some ideas for C binding from ADA.
> 
> Thanks.
> 
> 
>> ps: when i started writing the simplejpeglib binding for ADA.
>> i had a lot of interfacing problems du to the portability macros of the
>> jpeglib. (it's surely possible, but when i've started my binding, my C
>> interfacing Skills from ADA was poor).
>> So i decided in my design to build a simple C interface to make Ada
>> binding easier. This permit me to be "C structure independent" and provide a
>> more easy upgrade of the jpeglib.
> 
> This is a problem... and I haven't found a *convienant* way to solve 
> this (other than wrapping it up as you and Warren pointed out - thanks). 
>   Macros change this, that and the other.  My ada code would need to be 
> changed at the spec level on different platforms, compilers, etc... 
> yuck.  A more experienced Ada developer could probably organise it 
> better, but
> 
> All I really want to do now is *decode* and encode (at various 
> qualities) a jpeg (in RBG).  Later things might get more complicated, 
> but for now that's it.  I'm going to look at your lib again now I've got 
> a bit more time.

chris, it's difficult to add a quality parameter to SimpleJpegLib.
The SimpleJpegLib, gives you the RGB values of an encoded JPEG File.

Patrice

Re: Binding to C

[chris]

Patrice Freydiere wrote:
> 
> chris, it's difficult to add a quality parameter to SimpleJpegLib.
> The SimpleJpegLib, gives you the RGB values of an encoded JPEG File.

So it will decode, but quality varied encoding is out.  That's actually 
ok for this project.  The first iteration deals with getting an image 
into the processing lib (and gui front end).