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) 2002-2018, 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
32pragma Compiler_Unit_Warning;
33
34with Ada.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   for Big_Words_Ptr'Storage_Size use 0;
44   --  Array type used to access by words
45
46   type Byte is mod 2 ** 8;
47   --  Used to process operands by bytes
48
49   type Big_Bytes is array (Natural) of Byte;
50   type Big_Bytes_Ptr is access Big_Bytes;
51   for Big_Bytes_Ptr'Storage_Size use 0;
52   --  Array type used to access by bytes
53
54   function To_Big_Words is new
55     Ada.Unchecked_Conversion (System.Address, Big_Words_Ptr);
56
57   function To_Big_Bytes is new
58     Ada.Unchecked_Conversion (System.Address, Big_Bytes_Ptr);
59
60   -----------------
61   -- Str_Compare --
62   -----------------
63
64   function Str_Compare
65     (Left      : System.Address;
66      Right     : System.Address;
67      Left_Len  : Natural;
68      Right_Len : Natural) return Integer
69   is
70      Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);
71
72   begin
73      --  If operands are non-aligned, or length is too short, go by bytes
74
75      if (((Left or Right) and 2#11#) /= 0) or else Compare_Len < 4 then
76         return Str_Compare_Bytes (Left, Right, Left_Len, Right_Len);
77      end if;
78
79      --  Here we can go by words
80
81      declare
82         LeftP  : constant Big_Words_Ptr := To_Big_Words (Left);
83         RightP : constant Big_Words_Ptr := To_Big_Words (Right);
84         Clen4  : constant Natural       := Compare_Len / 4 - 1;
85         Clen4F : constant Natural       := Clen4 * 4;
86
87      begin
88         for J in 0 .. Clen4 loop
89            if LeftP (J) /= RightP (J) then
90               return Str_Compare_Bytes
91                        (Left  + Address (4 * J),
92                         Right + Address (4 * J),
93                         4, 4);
94            end if;
95         end loop;
96
97         return Str_Compare_Bytes
98                  (Left      + Address (Clen4F),
99                   Right     + Address (Clen4F),
100                   Left_Len  - Clen4F,
101                   Right_Len - Clen4F);
102      end;
103   end Str_Compare;
104
105   -----------------------
106   -- Str_Compare_Bytes --
107   -----------------------
108
109   function Str_Compare_Bytes
110     (Left      : System.Address;
111      Right     : System.Address;
112      Left_Len  : Natural;
113      Right_Len : Natural) 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