xapian-core/net/length.h

   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
  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