locate/frcode.c

   1 /* frcode -- front-compress a sorted list
   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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  17
  18 /* Usage: frcode < sorted-list > compressed-list
  19
  20    Uses front compression (also known as incremental encoding);
  21    see ";login:", March 1983, p. 8.
  22
  23    The input is a sorted list of NUL-terminated strings.
  24    (FIXME newline-terminated, until we figure out how to sort
  25    NUL-terminated strings.)
  26
  27    The output entries are in the same order as the input;
  28    each entry consists of an offset-differential count byte
  29    (the additional number of characters of prefix of the preceding entry to
  30    use beyond the number that the preceding entry is using of its predecessor),
  31    followed by a null-terminated ASCII remainder.
  32
  33    If the offset-differential count is larger than can be stored
  34    in a byte (+/-127), the byte has the value LOCATEDB_ESCAPE
  35    and the count follows in a 2-byte word, with the high byte first
  36    (network byte order).
  37
  38    Example:
  39
  40    Input, with NULs changed to newlines:
  41    /usr/src
  42    /usr/src/cmd/aardvark.c
  43    /usr/src/cmd/armadillo.c
  44    /usr/tmp/zoo
  45
  46    Length of the longest prefix of the preceding entry to share:
  47    0 /usr/src
  48    8 /cmd/aardvark.c
  49    14 rmadillo.c
  50    5 tmp/zoo
  51
  52    Output, with NULs changed to newlines and count bytes made printable:
  53    0 LOCATE02
  54    0 /usr/src
  55    8 /cmd/aardvark.c
  56    6 rmadillo.c
  57    -9 tmp/zoo
  58
  59    (6 = 14 - 8, and -9 = 5 - 14)
  60
  61    Written by James A. Woods <jwoods@adobe.com>.
  62    Modified by David MacKenzie <djm@gnu.ai.mit.edu>.  */
  63
  64 #include <config.h>
  65 #include <stdio.h>
  66 #include <sys/types.h>
  67
  68 #if defined(HAVE_STRING_H) || defined(STDC_HEADERS)
  69 #include <string.h>
  70 #else
  71 #include <strings.h>
  72 #endif
  73
  74 #ifdef STDC_HEADERS
  75 #include <stdlib.h>
  76 #endif
  77
  78 #include "locatedb.h"
  79 #include <getline.h>
  80
  81 char *xmalloc PARAMS((size_t));
  82
  83 /* The name this program was run with.  */
  84 char *program_name;
  85
  86 /* Write out a 16-bit int, high byte first (network byte order).  */
  87
  88 static void
  89 put_short (int c, FILE *fp)
  90 {
  91   putc (c >> 8, fp);
  92   putc (c, fp);
  93 }
  94
  95 /* Return the length of the longest common prefix of strings S1 and S2. */
  96
  97 static int
  98 prefix_length (char *s1, char *s2)
  99 {
 100   register char *start;
 101
 102   for (start = s1; *s1 == *s2 && *s1 != '\0'; s1++, s2++)
 103     ;
 104   return s1 - start;
 105 }
 106
 107 int
 108 main (int argc, char **argv)
 109 {
 110   char *path;                   /* The current input entry.  */
 111   char *oldpath;                /* The previous input entry.  */
 112   size_t pathsize, oldpathsize; /* Amounts allocated for them.  */
 113   int count, oldcount, diffcount; /* Their prefix lengths & the difference. */
 114   int line_len;                 /* Length of input line.  */
 115
 116   program_name = argv[0];
 117
 118   pathsize = oldpathsize = 1026; /* Increased as necessary by getline.  */
 119   path = xmalloc (pathsize);
 120   oldpath = xmalloc (oldpathsize);
 121
 122   /* Set to anything not starting with a slash, to force the first
 123      prefix count to 0.  */
 124   strcpy (oldpath, " ");
 125   oldcount = 0;
 126
 127   fwrite (LOCATEDB_MAGIC, sizeof (LOCATEDB_MAGIC), 1, stdout);
 128
 129   /* FIXME temporary: change the \n to \0 when we figure out how to sort
 130      null-terminated strings.  */
 131   while ((line_len = getline (&path, &pathsize, stdin)) > 0)
 132     {
 133       path[line_len - 1] = '\0'; /* FIXME temporary: nuke the newline.  */
 134
 135       count = prefix_length (oldpath, path);
 136       diffcount = count - oldcount;
 137       oldcount = count;
 138       /* If the difference is small, it fits in one byte;
 139          otherwise, two bytes plus a marker noting that fact.  */
 140       if (diffcount < -127 || diffcount > 127)
 141         {
 142           putc (LOCATEDB_ESCAPE, stdout);
 143           put_short (diffcount, stdout);
 144         }
 145       else
 146         putc (diffcount, stdout);
 147
 148       fputs (path + count, stdout);
 149       putc ('\0', stdout);
 150
 151       {
 152         /* Swap path and oldpath and their sizes.  */
 153         char *tmppath = oldpath;
 154         size_t tmppathsize = oldpathsize;
 155         oldpath = path;
 156         oldpathsize = pathsize;
 157         path = tmppath;
 158         pathsize = tmppathsize;
 159       }
 160     }
 161
 162   free (path);
 163   free (oldpath);
 164
 165   exit (0);
 166 }