src/closure.c

   1 /* Subroutines for bison
   2    Copyright (C) 1984, 1989, 2000, 2001, 2002 Free Software Foundation, Inc.
   3
   4    This file is part of Bison, the GNU Compiler Compiler.
   5
   6    Bison is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    Bison is distributed in the hope that it will be useful, but
  12    WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with Bison; see the file COPYING.  If not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  19    02111-1307, USA.  */
  20
  21 #include "system.h"
  22 #include "bitset.h"
  23 #include "bitsetv.h"
  24 #include "getargs.h"
  25 #include "symtab.h"
  26 #include "gram.h"
  27 #include "reader.h"
  28 #include "closure.h"
  29 #include "derives.h"
  30 #include "warshall.h"
  31
  32 /* NITEMSET is the size of the array ITEMSET.  */
  33 short *itemset;
  34 int nitemset;
  35
  36 static bitset ruleset;
  37
  38 /* internal data.  See comments before set_fderives and set_firsts.  */
  39 static bitsetv fderives = NULL;
  40 static bitsetv firsts = NULL;
  41
  42 /* Retrieve the FDERIVES/FIRSTS sets of the nonterminals numbered Var.  */
  43 #define FDERIVES(Var)   fderives[(Var) - ntokens]
  44 #define   FIRSTS(Var)   firsts[(Var) - ntokens]
  45 \f
  46
  47 /*-----------------.
  48 | Debugging code.  |
  49 `-----------------*/
  50
  51 static void
  52 print_closure (const char *title, short *array, size_t size)
  53 {
  54   size_t i;
  55   fprintf (stderr, "Closure: %s\n", title);
  56   for (i = 0; i < size; ++i)
  57     {
  58       short *rp;
  59       fprintf (stderr, "  %2d: .", array[i]);
  60       for (rp = &ritem[array[i]]; *rp >= 0; ++rp)
  61         fprintf (stderr, " %s", symbols[*rp]->tag);
  62       fprintf (stderr, "  (rule %d)\n", -*rp - 1);
  63     }
  64   fputs ("\n\n", stderr);
  65 }
  66
  67
  68 static void
  69 print_firsts (void)
  70 {
  71   int i, j;
  72
  73   fprintf (stderr, "FIRSTS\n");
  74   for (i = ntokens; i < nsyms; i++)
  75     {
  76       fprintf (stderr, "\t%s firsts\n", symbols[i]->tag);
  77       for (j = 0; j < nvars; j++)
  78         if (bitset_test (FIRSTS (i), j))
  79           fprintf (stderr, "\t\t%d (%s)\n",
  80                    j + ntokens, symbols[j + ntokens]->tag);
  81     }
  82   fprintf (stderr, "\n\n");
  83 }
  84
  85
  86 static void
  87 print_fderives (void)
  88 {
  89   int i, j;
  90
  91   fprintf (stderr, "FDERIVES\n");
  92   for (i = ntokens; i < nsyms; i++)
  93     {
  94       fprintf (stderr, "\t%s derives\n", symbols[i]->tag);
  95       for (j = 0; j <= nrules; j++)
  96         if (bitset_test (FDERIVES (i), j))
  97           {
  98             short *rhsp;
  99             fprintf (stderr, "\t\t%d:", j - 1);
 100             for (rhsp = &ritem[rules[j].rhs]; *rhsp >= 0; ++rhsp)
 101               fprintf (stderr, " %s", symbols[*rhsp]->tag);
 102             fputc ('\n', stderr);
 103           }
 104     }
 105   fprintf (stderr, "\n\n");
 106 }
 107 \f
 108 /*------------------------------------------------------------------.
 109 | Set FIRSTS to be an NVARS array of NVARS bitsets indicating which |
 110 | items can represent the beginning of the input corresponding to   |
 111 | which other items.                                                |
 112 |                                                                   |
 113 | For example, if some rule expands symbol 5 into the sequence of   |
 114 | symbols 8 3 20, the symbol 8 can be the beginning of the data for |
 115 | symbol 5, so the bit [8 - ntokens] in first[5 - ntokens] (= FIRST |
 116 | (5)) is set.                                                      |
 117 `------------------------------------------------------------------*/
 118
 119 static void
 120 set_firsts (void)
 121 {
 122   int i, j;
 123
 124   firsts = bitsetv_create (nvars, nvars, BITSET_FIXED);
 125
 126   for (i = ntokens; i < nsyms; i++)
 127     for (j = 0; derives[i][j] >= 0; ++j)
 128       {
 129         int symbol = ritem[rules[derives[i][j]].rhs];
 130         if (ISVAR (symbol))
 131           bitset_set (FIRSTS (i), symbol - ntokens);
 132       }
 133
 134   RTC (firsts);
 135
 136   if (trace_flag)
 137     print_firsts ();
 138 }
 139
 140 /*-------------------------------------------------------------------.
 141 | Set FDERIVES to an NVARS by NRULES matrix of bits indicating which |
 142 | rules can help derive the beginning of the data for each           |
 143 | nonterminal.                                                       |
 144 |                                                                    |
 145 | For example, if symbol 5 can be derived as the sequence of symbols |
 146 | 8 3 20, and one of the rules for deriving symbol 8 is rule 4, then |
 147 | the [5 - NTOKENS, 4] bit in FDERIVES is set.                       |
 148 `-------------------------------------------------------------------*/
 149
 150 static void
 151 set_fderives (void)
 152 {
 153   int i, j, k;
 154
 155   fderives = bitsetv_create (nvars, nrules + 1, BITSET_FIXED);
 156
 157   set_firsts ();
 158
 159   for (i = ntokens; i < nsyms; ++i)
 160     for (j = ntokens; j < nsyms; ++j)
 161       if (bitset_test (FIRSTS (i), j - ntokens))
 162         for (k = 0; derives[j][k] > 0; ++k)
 163           bitset_set (FDERIVES (i), derives[j][k]);
 164
 165   if (trace_flag)
 166     print_fderives ();
 167
 168   bitsetv_free (firsts);
 169 }
 170 \f
 171
 172 void
 173 new_closure (int n)
 174 {
 175   itemset = XCALLOC (short, n);
 176
 177   ruleset = bitset_create (nrules + 1, BITSET_FIXED);
 178
 179   set_fderives ();
 180 }
 181
 182
 183
 184 void
 185 closure (short *core, int n)
 186 {
 187   /* Index over CORE. */
 188   int c;
 189
 190   /* An index over RULESET. */
 191   int r;
 192
 193   /* A bit index over RULESET. */
 194   int ruleno;
 195
 196   if (trace_flag)
 197     print_closure ("input", core, n);
 198
 199   if (n == 0)
 200     {
 201       bitset_copy (ruleset, FDERIVES (start_symbol));
 202     }
 203   else
 204     {
 205       bitset_zero (ruleset);
 206
 207       for (c = 0; c < n; ++c)
 208         if (ISVAR (ritem[core[c]]))
 209           bitset_or (ruleset, ruleset, FDERIVES (ritem[core[c]]));
 210     }
 211
 212   nitemset = 0;
 213   c = 0;
 214   for (ruleno = 0; ruleno < nrules + 1; ++ruleno)
 215     if (bitset_test (ruleset, ruleno))
 216       {
 217         int itemno = rules[ruleno].rhs;
 218         while (c < n && core[c] < itemno)
 219           {
 220             itemset[nitemset] = core[c];
 221             nitemset++;
 222             c++;
 223           }
 224         itemset[nitemset] = itemno;
 225         nitemset++;
 226       }
 227
 228   while (c < n)
 229     {
 230       itemset[nitemset] = core[c];
 231       nitemset++;
 232       c++;
 233     }
 234
 235   if (trace_flag)
 236     print_closure ("output", itemset, nitemset);
 237 }
 238
 239
 240 void
 241 free_closure (void)
 242 {
 243   XFREE (itemset);
 244   bitset_free (ruleset);
 245   bitsetv_free (fderives);
 246 }