1 /** @file length.h
2 * @brief length encoded as a string
3 */
4 /* Copyright (C) 2006,2007,2008,2009,2012,2015 Olly Betts
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20
21 #ifndef XAPIAN_INCLUDED_LENGTH_H
22 #define XAPIAN_INCLUDED_LENGTH_H
23
24 #include <string>
25
26 /** Encode a length as a variable-length string.
27 *
28 * The encoding specifies its own length.
29 *
30 * @param len The length to encode.
31 *
32 * @return The encoded length.
33 */
34 template<class T>
35 std::string
encode_length(T len)36 encode_length(T len)
37 {
38 std::string result;
39 if (len < 255) {
40 result += static_cast<unsigned char>(len);
41 } else {
42 result += '\xff';
43 len -= 255;
44 while (true) {
45 unsigned char b = static_cast<unsigned char>(len & 0x7f);
46 len >>= 7;
47 if (!len) {
48 result += char(b | static_cast<unsigned char>(0x80));
49 break;
50 }
51 result += b;
52 }
53 }
54 return result;
55 }
56
57 /** Decode a length encoded by encode_length.
58 *
59 * @param p Pointer to a pointer to the string, which will be advanced past
60 * the encoded length.
61 * @param end Pointer to the end of the string.
62 * @param[out] out The decoded length.
63 */
64 void decode_length(const char ** p, const char *end, unsigned & out);
65
66 void decode_length(const char ** p, const char *end, unsigned long & out);
67
68 void decode_length(const char ** p, const char *end, unsigned long long & out);
69
70 /** Decode a length encoded by encode_length.
71 *
72 * Also checks the result against the amount of data remaining after the
73 * length has been decoded.
74 *
75 * @param p Pointer to a pointer to the string, which will be advanced past
76 * the encoded length.
77 * @param end Pointer to the end of the string.
78 * @param[out] out The decoded length.
79 */
80 void decode_length_and_check(const char ** p, const char *end, unsigned & out);
81
82 void decode_length_and_check(const char ** p, const char *end,
83 unsigned long & out);
84
85 void decode_length_and_check(const char ** p, const char *end,
86 unsigned long long & out);
87
88 #endif // XAPIAN_INCLUDED_LENGTH_H
89