mdw@git.distorted.org.uk Git - anag/blob - mono.c

   1 /* -*-c-*-
   2  *
   3  * Monoalphabetic matcher
   4  *
   5  * (c) 2003 Mark Wooding
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Anag: a simple wordgame helper.
  11  *
  12  * Anag is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * Anag is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with Anag; if not, write to the Free Software Foundation,
  24  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 /*----- Header files ------------------------------------------------------*/
  28
  29 #include "anag.h"
  30
  31 /*----- Data structures ---------------------------------------------------*/
  32
  33 typedef struct node_mono {
  34   node n;
  35   unsigned len;
  36   unsigned char *p;
  37 } node_mono;
  38
  39 /*----- Main code ---------------------------------------------------------*/
  40
  41 /* --- Matching --- */
  42
  43 static int n_mono(node *nn, const char *p, size_t sz)
  44 {
  45   node_mono *n = (node_mono *)nn;
  46   unsigned map[UCHAR_MAX];
  47   const unsigned char *q = n->p;
  48   unsigned max = 0;
  49   int ch;
  50
  51   /* Monoalphabetic substitution preserves length. */
  52   if (sz != n->len) return (0);
  53
  54   /* Canonicalize this string as we did the pattern.  Fail if we find a
  55    * mismatch.
  56    */
  57   memset(map, UCHAR_MAX, sizeof(map));
  58   while (*p) {
  59     ch = *p++;
  60     if (map[ch] >= max) map[ch] = max++;
  61     if (max >= UCHAR_MAX) return (0);
  62     if (*q++ != map[ch]) return (0);
  63   }
  64   return (1);
  65 }
  66
  67 /* --- Node creation --- */
  68
  69 node *mono(const char *const *av)
  70 {
  71   unsigned char map[UCHAR_MAX];
  72   const char *p = av[0];
  73   unsigned char *q;
  74   unsigned max = 0;
  75   int ch;
  76
  77   node_mono *n = xmalloc(sizeof(*n));
  78   n->n.func = n_mono;
  79   n->p = q = xmalloc(n->len);
  80   n->len = strlen(p);
  81
  82   /* Convert the string into the canonical representative of its equivalence
  83    * class, specifically the lexically first string which is equivalent under
  84    * monoalphabetic substitution.  That is: replace the first distinct
  85    * character with zero, the second with one, and so on.
  86    */
  87   memset(map, UCHAR_MAX, sizeof(map));
  88   while (*p) {
  89     ch = *p++;
  90     if (map[ch] >= max) map[ch] = max++;
  91     assert(max < UCHAR_MAX);
  92     *q++ = map[ch];
  93   }
  94
  95   return (&n->n);
  96 }
  97
  98 /*----- That's all, folks -------------------------------------------------*/