gcc/ada/libgnat/s-strcom.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                    GNAT RUN-TIME LIBRARY COMPONENTS                      --
   4 --                                                                          --
   5 --                S Y S T E M . S T R I N G _ C O M P A R E                 --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 2002-2023, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 with Ada.Unchecked_Conversion;
  33
  34 package body System.String_Compare is
  35
  36    type Word is mod 2 ** 32;
  37    --  Used to process operands by words
  38
  39    type Big_Words is array (Natural) of Word;
  40    type Big_Words_Ptr is access Big_Words;
  41    for Big_Words_Ptr'Storage_Size use 0;
  42    --  Array type used to access by words
  43
  44    type Byte is mod 2 ** 8;
  45    --  Used to process operands by bytes
  46
  47    type Big_Bytes is array (Natural) of Byte;
  48    type Big_Bytes_Ptr is access Big_Bytes;
  49    for Big_Bytes_Ptr'Storage_Size use 0;
  50    --  Array type used to access by bytes
  51
  52    function To_Big_Words is new
  53      Ada.Unchecked_Conversion (System.Address, Big_Words_Ptr);
  54
  55    function To_Big_Bytes is new
  56      Ada.Unchecked_Conversion (System.Address, Big_Bytes_Ptr);
  57
  58    -----------------
  59    -- Str_Compare --
  60    -----------------
  61
  62    function Str_Compare
  63      (Left      : System.Address;
  64       Right     : System.Address;
  65       Left_Len  : Natural;
  66       Right_Len : Natural) return Integer
  67    is
  68       Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);
  69
  70    begin
  71       --  If operands are non-aligned, or length is too short, go by bytes
  72
  73       if (((Left or Right) and 2#11#) /= 0) or else Compare_Len < 4 then
  74          return Str_Compare_Bytes (Left, Right, Left_Len, Right_Len);
  75       end if;
  76
  77       --  Here we can go by words
  78
  79       declare
  80          LeftP  : constant Big_Words_Ptr := To_Big_Words (Left);
  81          RightP : constant Big_Words_Ptr := To_Big_Words (Right);
  82          Clen4  : constant Natural       := Compare_Len / 4 - 1;
  83          Clen4F : constant Natural       := Clen4 * 4;
  84
  85       begin
  86          for J in 0 .. Clen4 loop
  87             if LeftP (J) /= RightP (J) then
  88                return Str_Compare_Bytes
  89                         (Left  + Address (4 * J),
  90                          Right + Address (4 * J),
  91                          4, 4);
  92             end if;
  93          end loop;
  94
  95          return Str_Compare_Bytes
  96                   (Left      + Address (Clen4F),
  97                    Right     + Address (Clen4F),
  98                    Left_Len  - Clen4F,
  99                    Right_Len - Clen4F);
 100       end;
 101    end Str_Compare;
 102
 103    -----------------------
 104    -- Str_Compare_Bytes --
 105    -----------------------
 106
 107    function Str_Compare_Bytes
 108      (Left      : System.Address;
 109       Right     : System.Address;
 110       Left_Len  : Natural;
 111       Right_Len : Natural) return Integer
 112    is
 113       Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);
 114
 115       LeftP  : constant Big_Bytes_Ptr := To_Big_Bytes (Left);
 116       RightP : constant Big_Bytes_Ptr := To_Big_Bytes (Right);
 117
 118    begin
 119       for J in 0 .. Compare_Len - 1 loop
 120          if LeftP (J) /= RightP (J) then
 121             if LeftP (J) > RightP (J) then
 122                return +1;
 123             else
 124                return -1;
 125             end if;
 126          end if;
 127       end loop;
 128
 129       if Left_Len = Right_Len then
 130          return 0;
 131       elsif Left_Len > Right_Len then
 132          return +1;
 133       else
 134          return -1;
 135       end if;
 136    end Str_Compare_Bytes;
 137
 138 end System.String_Compare;