1------------------------------------------------------------------------------
2--                                                                          --
3--                   GNU ADA RUNTIME 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--                                 S p e c                                  --
8--                                                                          --
9--             Copyright (C) 2002 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 2,  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.  See the GNU General Public License --
17-- for  more details.  You should have  received  a copy of the GNU General --
18-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
19-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
20-- MA 02111-1307, USA.                                                      --
21--                                                                          --
22-- As a special exception,  if other files  instantiate  generics from this --
23-- unit, or you link  this unit with other files  to produce an executable, --
24-- this  unit  does not  by itself cause  the resulting  executable  to  be --
25-- covered  by the  GNU  General  Public  License.  This exception does not --
26-- however invalidate  any other reasons why  the executable file  might be --
27-- covered by the  GNU Public License.                                      --
28--                                                                          --
29-- GNAT was originally developed  by the GNAT team at  New York University. --
30-- Extensive contributions were provided by Ada Core Technologies Inc.      --
31--                                                                          --
32------------------------------------------------------------------------------
33
34with Unchecked_Conversion;
35
36package body System.String_Compare is
37
38   type Word is mod 2 ** 32;
39   --  Used to process operands by words
40
41   type Big_Words is array (Natural) of Word;
42   type Big_Words_Ptr is access Big_Words;
43   --  Array type used to access by words
44
45   type Byte is mod 2 ** 8;
46   --  Used to process operands by bytes
47
48   type Big_Bytes is array (Natural) of Byte;
49   type Big_Bytes_Ptr is access Big_Bytes;
50   --  Array type used to access by bytes
51
52   function To_Big_Words is new
53     Unchecked_Conversion (System.Address, Big_Words_Ptr);
54
55   function To_Big_Bytes is new
56     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)
67      return      Integer
68   is
69      Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);
70
71   begin
72      --  If operands are non-aligned, or length is too short, go by bytes
73
74      if (((Left or Right) and 2#11#) /= 0) or else Compare_Len < 4 then
75         return Str_Compare_Bytes (Left, Right, Left_Len, Right_Len);
76      end if;
77
78      --  Here we can go by words
79
80      declare
81         LeftP  : constant Big_Words_Ptr := To_Big_Words (Left);
82         RightP : constant Big_Words_Ptr := To_Big_Words (Right);
83         Clen4  : constant Natural       := Compare_Len / 4 - 1;
84         Clen4F : constant Natural       := Clen4 * 4;
85
86      begin
87         for J in 0 .. Clen4 loop
88            if LeftP (J) /= RightP (J) then
89               return Str_Compare_Bytes
90                        (Left  + Address (4 * J),
91                         Right + Address (4 * J),
92                         4, 4);
93            end if;
94         end loop;
95
96         return Str_Compare_Bytes
97                  (Left      + Address (Clen4F),
98                   Right     + Address (Clen4F),
99                   Left_Len  - Clen4F,
100                   Right_Len - Clen4F);
101      end;
102   end Str_Compare;
103
104   -----------------------
105   -- Str_Compare_Bytes --
106   -----------------------
107
108   function Str_Compare_Bytes
109     (Left      : System.Address;
110      Right     : System.Address;
111      Left_Len  : Natural;
112      Right_Len : Natural)
113      return      Integer
114   is
115      Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);
116
117      LeftP  : constant Big_Bytes_Ptr := To_Big_Bytes (Left);
118      RightP : constant Big_Bytes_Ptr := To_Big_Bytes (Right);
119
120   begin
121      for J in 0 .. Compare_Len - 1 loop
122         if LeftP (J) /= RightP (J) then
123            if LeftP (J) > RightP (J) then
124               return +1;
125            else
126               return -1;
127            end if;
128         end if;
129      end loop;
130
131      if Left_Len = Right_Len then
132         return 0;
133      elsif Left_Len > Right_Len then
134         return +1;
135      else
136         return -1;
137      end if;
138   end Str_Compare_Bytes;
139
140end System.String_Compare;
141