Efficient Stream_IO

Efficient Stream_IO

[Lutz Donnerhacke]

Is there a portable way to implement efficient IO on streams?
Especially String to Stream_Element_Array conversions?

I do have the problem, that my Ada implementation of a netflow collector
requires considerably more CPU cycles than the C implementation. Of course,
I have to profile the code in detail, but I suspect String'Read/Write as
iterated Character'Reads/Writes as a major contribution.

An unportable implementation would be:

-- Don't do this!
procedure Put(Stream : access Root_Stream_Type'Class; s : String) is
  data : Stream_Element_Array(1 .. s'Length);
  pragma Import(Ada, data);
  for data'Address use s'Address;
  pragma Assert(Stream_Element_Array'Component_Size = String'Component_Size);
  pragma Assert(data'Size = s'Size);
begin
  Write(Stream, data);
end Put;

Re: Efficient Stream_IO

[Stephen Leake]

Lutz Donnerhacke <lutz@iks-jena.de> writes:

> Is there a portable way to implement efficient IO on streams?

Depends on how wide a range of hardware and OS you mean by "portable".

The Ada language tries hard to be portable to no OS, hardware that has
39 bit "bytes", hardware that has ones-complement integer arithmetic,
etc.

If you restrict "portable" to mean an OS with a TCP stack, and
hardware with 8 bit bytes, things are much simpler. In fact, the code
you wrote is probably portable among that set.

-- 
-- Stephe

Re: Efficient Stream_IO

[Lutz Donnerhacke]

* Stephen Leake wrote:
> Lutz Donnerhacke <lutz@iks-jena.de> writes:
>> Is there a portable way to implement efficient IO on streams?
>
> Depends on how wide a range of hardware and OS you mean by "portable".

Real world justification of programmer's attitute:
 It has to be run on a single maschine, specified by the programmer and
 configured as the programmer wishes. It will be an ordinary x86 based
 server from the shelf. The server can be used as initial development
 enviroment. For further developments a simiar maschine will exists.

> The Ada language tries hard to be portable to no OS, hardware that has
> 39 bit "bytes", hardware that has ones-complement integer arithmetic,
> etc.

And how will one convert from String to Stream_Element_Array?
Using String'Output to a self defined, trivial Memory_Stream?

I know the benefits of this approach very well. Instead of mapping a type to
Storage_Element_Array or Stream_Element_Array, the 'Read and 'Write
attributes vanish any alignment and representation problem. That's great and
slow.

> If you restrict "portable" to mean an OS with a TCP stack, and hardware
> with 8 bit bytes, things are much simpler. In fact, the code you wrote is
> probably portable among that set.

Thank you.

Re: Efficient Stream_IO

[Pascal Obry]

Lutz Donnerhacke <lutz@iks-jena.de> writes:

> And how will one convert from String to Stream_Element_Array?

With a loop if Stream_Element'Size /= Character'Size and with a simple
Unchecked_Conversion otherwise. The second solution is very fast and will
work in 99,9% (100%???) of the cases.

Pascal.

-- 

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Re: Efficient Stream_IO

[Martin Dowie]

Pascal Obry <pascal@obry.org> wrote in message news:<uhdvmgwt4.fsf@obry.org>...
> Lutz Donnerhacke <lutz@iks-jena.de> writes:
> 
> > And how will one convert from String to Stream_Element_Array?
> 
> With a loop if Stream_Element'Size /= Character'Size and with a simple
> Unchecked_Conversion otherwise. The second solution is very fast and will
> work in 99,9% (100%???) of the cases.

You don't even need a loop if one is a multiple of the other, which
is, I guess, the most likely scenario.