Re: Ada bench : count words

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 22 Mar 2005 11:57:22 +0000, Marius Amado Alves wrote:

>>> ... To implement buffering, I have resorted to
>>> Ada.Direct_IO, which I think cannot apply to standard input.
>>
>> Is Text_IO that bad?
> 
> No, if you can solve The Get_Line puzzle :-)

What about Get (Item : out Character)?

I wonder if calling C-lib's read would qualify! (:-))

>>>     procedure Process (S : in String) is
>>>     begin
>>>        Lines := Lines + Ada.Strings.Fixed.Count (S, EOL);
>>
>> Isn't it an extra pass? I think you should do parsing using FSM.
>> Character
>> classes are: EOL, delimiter, letter. It is either two character map 
>> tests
>> or one case statement. I don't know what is faster. Probably you should
>> test both.
>>
>>>        for I in S'Range loop
>>>           if Is_Separator (S (I)) then
>>>              if In_Word then Finish_Word; end if;
>>>           else
>>>              if not In_Word then Start_Word; end if;
>>>           end if;
>>>        end loop;
>>>     end;
> 
> Note EOL is not a character, but a string, because in some environments 
> the thing is a combination of two characters.

I think Text_IO should translate it into LF. But anyway you can always
assume LF = new line, CR = space in the FSM.

> This one-character 
> version improves speed (but still only to 1/2 of C):
> 
>           for I in S'Range loop
>              if S (I) = EOL then Lines := Lines + 1; end if;
>              if Is_Separator (S (I)) then
>                 if In_Word then Finish_Word; end if;
>              else
>                 if not In_Word then Start_Word; end if;
>              end if;
>           end loop;
> 
> I have not tried with string matching (if that's what you mean with 
> "FSM") because the iteration was already there, and I doubt the 
> standard library implements it more efficiently than that.

No, I meant a finite state machine:

<<Word>>
   read character;
   case Char is
      when EOL    => Inc line count; goto Blank;
      when Space => goto Blank;
      when Letter => goto Word;
   end case;

<<Blank>>
   read character;
   case Char is
      when EOL    => Inc line count; goto Blank;
      when Space => goto Blank;
      when Letter => Inc word count; goto Word;
   end case;

<<Word>>
   read character;
   case Char is
      when EOL    => Inc line count; goto Blank;
      when Space => goto Blank;
      when Letter => goto Word;
   end case;

FSM is one of that rare cases where gotos are natural. What a pity that Ada
does not have arrays of labels! (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de