gcc/ada/a-cgaaso.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT LIBRARY COMPONENTS                          --
   4 --                                                                          --
   5 --               ADA.CONTAINERS.GENERIC_ANONYMOUS_ARRAY_SORT                --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --             Copyright (C) 2004 Free Software Foundation, Inc.            --
  10 --                                                                          --
  11 -- This specification is derived from the Ada Reference Manual for use with --
  12 -- GNAT. The copyright notice above, and the license provisions that follow --
  13 -- apply solely to the  contents of the part following the private keyword. --
  14 --                                                                          --
  15 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  16 -- terms of the  GNU General Public License as published  by the Free Soft- --
  17 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  18 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  19 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  20 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  21 -- for  more details.  You should have  received  a copy of the GNU General --
  22 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  23 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  24 -- MA 02111-1307, USA.                                                      --
  25 --                                                                          --
  26 -- As a special exception,  if other files  instantiate  generics from this --
  27 -- unit, or you link  this unit with other files  to produce an executable, --
  28 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  29 -- covered  by the  GNU  General  Public  License.  This exception does not --
  30 -- however invalidate  any other reasons why  the executable file  might be --
  31 -- covered by the  GNU Public License.                                      --
  32 --                                                                          --
  33 -- This unit was originally developed by Matthew J Heaney.                  --
  34 ------------------------------------------------------------------------------
  35
  36 procedure Ada.Containers.Generic_Anonymous_Array_Sort
  37   (First, Last : Index_Type'Base)
  38 is
  39    Pivot, Lo, Mid, Hi : Index_Type;
  40
  41 begin
  42    if Last <= First then
  43       return;
  44    end if;
  45
  46    Lo := First;
  47    Hi := Last;
  48
  49    if Last = Index_Type'Succ (First) then
  50       if not Less (Lo, Hi) then
  51          Swap (Lo, Hi);
  52       end if;
  53
  54       return;
  55    end if;
  56
  57    Mid := Index_Type'Val
  58      (Index_Type'Pos (Lo) +
  59       (Index_Type'Pos (Hi) - Index_Type'Pos (Lo)) / 2);
  60
  61    --  We need to figure out which case we have:
  62    --  x < y < z
  63    --  x < z < y
  64    --  z < x < y
  65    --  y < x < z
  66    --  y < z < x
  67    --  z < y < x
  68
  69    if Less (Lo, Mid) then
  70       if Less (Lo, Hi) then
  71          if Less (Mid, Hi) then
  72             Swap (Lo, Mid);
  73
  74          else
  75             Swap (Lo, Hi);
  76
  77          end if;
  78
  79       else
  80          null;  --  lo is median
  81       end if;
  82
  83    elsif Less (Lo, Hi) then
  84       null; --  lo is median
  85
  86    elsif Less (Mid, Hi) then
  87       Swap (Lo, Hi);
  88
  89    else
  90       Swap (Lo, Mid);
  91    end if;
  92
  93    Pivot := Lo;
  94    Outer : loop
  95       loop
  96          exit Outer when not (Pivot < Hi);
  97
  98          if Less (Hi, Pivot) then
  99             Swap (Hi, Pivot);
 100             Pivot := Hi;
 101             Lo := Index_Type'Succ (Lo);
 102             exit;
 103          else
 104             Hi := Index_Type'Pred (Hi);
 105          end if;
 106       end loop;
 107
 108       loop
 109          exit Outer when not (Lo < Pivot);
 110
 111          if Less (Lo, Pivot) then
 112             Lo := Index_Type'Succ (Lo);
 113          else
 114             Swap (Lo, Pivot);
 115             Pivot := Lo;
 116             Hi := Index_Type'Pred (Hi);
 117             exit;
 118          end if;
 119       end loop;
 120    end loop Outer;
 121
 122    Generic_Anonymous_Array_Sort (First, Index_Type'Pred (Pivot));
 123    Generic_Anonymous_Array_Sort (Index_Type'Succ (Pivot), Last);
 124
 125 end Ada.Containers.Generic_Anonymous_Array_Sort;