File : 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) 2002-2013, 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 -- --
19 -- --
20 -- --
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 pragma Compiler_Unit_Warning;
33
34 with Ada.Unchecked_Conversion;
35
36 package 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
140 end System.String_Compare;