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Date: Thu, 29 Sep 2005 16:05:26 +0200
From: Georg Bauhaus <bauhaus@futureapps.de>
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Newsgroups: comp.lang.ada
Subject: Re: String filtering
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Date: 2005-09-29T16:03:57+02:00
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David Trudgett wrote:

> 
>>Good.  It makes the String and Unbounded_String versions practically
>>equivalent - probably both in CPU and memory use.
> 
> 
> Much of a muchness, I would guess. Profiling particular applications
> on particular compilers is the only way to tell for sure, though.

Got some figures. As expected, String is always faster than Unbounded_String.
Maybe surprisingly, Vector is somewhat faster than Unbounded_String
in all cases, provided inlining is used. Heap means the String objects
have been allocated using new.
Compiler is GCC 4.1 on GNU/Linux x86.

-O2 -gnatn -gnato:

 1. iteration, 10 chars, 1000000 runs.
Fixed:      2.084710000
Heap:       1.498224000
Unbounded:  7.608056000
Vector:     5.686385000
 2. iteration, 10000 chars, 1000 runs.
Fixed:      0.421747000
Heap:       0.477814000
Unbounded:  0.787875000
Vector:     0.515643000
 3. iteration, 1000000 chars, 10 runs.
Fixed:      0.560290000
Heap:       0.622039000
Unbounded:  1.137758000
Vector:     0.917281000

-O2 -gnato

 1. iteration, 10 chars, 1000000 runs.
Fixed:      1.730108000
Heap:       1.604875000
Unbounded:  7.659804000
Vector:     6.483596000
 2. iteration, 10000 chars, 1000 runs.
Fixed:      0.510872000
Heap:       0.566339000
Unbounded:  0.872703000
Vector:     1.044757000
 3. iteration, 1000000 chars, 10 runs.
Fixed:      0.650525000
Heap:       0.710203000
Unbounded:  1.213516000
Vector:     1.437887000


The Vector function uses Vec_String in place of Unbounded_String,
where subtype Vec_String is Character_Vectors.Vector:


   function Strip_Non_Alphanumeric
     (Str: in Vec_String) return Vec_String
   is
      use Character_Vectors, Ada.Containers;

      Dest_Char: Index_Subtype'Base := 0;
      New_Str: Vec_String;
      Dest_Size: constant Count_Type := Length(Str);

   begin
      if Dest_Size > 0 then
         New_Str := To_Vector(Dest_Size);
         for Src_Char in 1 .. Last_Index(Str) loop
            if Is_In(Element(Str, Src_Char), Alpha_Num_Space_Set) then
               Dest_Char := Dest_Char + 1;
               Replace_Element
                 (New_Str, Dest_Char, Element(Str, Src_Char));
            end if;
         end loop;
      else
         null;
      end if;
      return New_Str;
   end Strip_Non_Alphanumeric;