locate/locatedb.h

   1 /* locatedb.h -- declarations for the locate database
   2    Copyright (C) 1994 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software
  16    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  17    USA.
  18 */
  19
  20 #ifndef _LOCATEDB_H
  21 #define _LOCATEDB_H 1
  22
  23 /* The magic string at the start of a locate database, to make sure
  24    it's in the right format.  The 02 is the database format version number.
  25    This string has the same format as a database entry, but you can't
  26    concatenate databases even if you remove it, since the differential count
  27    in the first entry of the second database will be wrong.  */
  28 #define LOCATEDB_MAGIC "\0LOCATE02"
  29
  30 /* Common-prefix length differences in the ranges
  31    0..127, -127..-1 (0x00..0x7f, 0x81..0xff) fit into one byte.
  32    This value (which is -128) indicates that the difference is
  33    too large to fit into one byte, and a two-byte integer follows.  */
  34 #define LOCATEDB_ESCAPE 0x80
  35 #define LOCATEDB_ONEBYTE_MAX (127)
  36 #define LOCATEDB_ONEBYTE_MIN (-127)
  37
  38
  39 /* If it is ever possible to try to encode LOCATEDB_MAGIC as a
  40  * single-byte offset, then an unfortunate length of common prefix
  41  * will produce a spurious escape character, desynchronising the data
  42  * stream.  We use a compile-time check in the preprocessor to prevent
  43  * this.
  44  */
  45 #if LOCATEDB_ESCAPE <= LOCATEDB_ONEBYTE_MAX
  46 #error "You have a bad combination of LOCATEDB_ESCAPE and LOCATEDB_ONEBYTE_MAX, see above"
  47 #endif
  48
  49 /* These are used for old, bigram-encoded databases:  */
  50
  51 /* Means the differential count follows in a 2-byte int instead. */
  52 #define LOCATEDB_OLD_ESCAPE     30
  53
  54 /* Offset added to differential counts to encode them as positive numbers.  */
  55 #define LOCATEDB_OLD_OFFSET     14
  56
  57 # ifndef PARAMS
  58 #  if defined PROTOTYPES || (defined __STDC__ && __STDC__)
  59 #   define PARAMS(Args) Args
  60 #  else
  61 #   define PARAMS(Args) ()
  62 #  endif
  63 # endif
  64
  65
  66 #define SLOCATE_DB_MAGIC_LEN 2
  67
  68 #endif /* !_LOCATEDB_H */