src/closure.c

   1 /* Subroutines for bison
   2    Copyright 1984, 1989, 2000, 2001 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 "getargs.h"
  23 #include "symtab.h"
  24 #include "gram.h"
  25 #include "reader.h"
  26 #include "closure.h"
  27 #include "derives.h"
  28 #include "bitset.h"
  29 #include "warshall.h"
  30
  31 /* NITEMSET is the size of the array ITEMSET.  */
  32 short *itemset;
  33 int nitemset;
  34
  35 static bitset ruleset;
  36
  37 /* internal data.  See comments before set_fderives and set_firsts.  */
  38 static bitset *fderives = NULL;
  39 static bitset *firsts = NULL;
  40
  41 /* Retrieve the FDERIVES/FIRSTS sets of the nonterminals numbered Var.  */
  42 #define FDERIVES(Var)   fderives[(Var) - ntokens]
  43 #define   FIRSTS(Var)   firsts[(Var) - ntokens]
  44 \f
  45
  46 /*-----------------.
  47 | Debugging code.  |
  48 `-----------------*/
  49
  50 static void
  51 print_closure (const char *title, short *array, size_t size)
  52 {
  53   size_t i;
  54   fprintf (stderr, "Closure: %s\n", title);
  55   for (i = 0; i < size; ++i)
  56     {
  57       short *rp;
  58       fprintf (stderr, "  %2d: .", array[i]);
  59       for (rp = &ritem[array[i]]; *rp >= 0; ++rp)
  60         fprintf (stderr, " %s", symbols[*rp]->tag);
  61       fprintf (stderr, "  (rule %d)\n", -*rp - 1);
  62     }
  63   fputs ("\n\n", stderr);
  64 }
  65
  66
  67 static void
  68 print_firsts (void)
  69 {
  70   int i, j;
  71
  72   fprintf (stderr, "FIRSTS\n");
  73   for (i = ntokens; i < nsyms; i++)
  74     {
  75       fprintf (stderr, "\t%s firsts\n", symbols[i]->tag);
  76       for (j = 0; j < nvars; j++)
  77         if (bitset_test (FIRSTS (i), j))
  78           fprintf (stderr, "\t\t%d (%s)\n",
  79                    j + ntokens, symbols[j + ntokens]->tag);
  80     }
  81   fprintf (stderr, "\n\n");
  82 }
  83
  84
  85 static void
  86 print_fderives (void)
  87 {
  88   int i, j;
  89
  90   fprintf (stderr, "FDERIVES\n");
  91   for (i = ntokens; i < nsyms; i++)
  92     {
  93       fprintf (stderr, "\t%s derives\n", symbols[i]->tag);
  94       for (j = 0; j <= nrules; j++)
  95         if (bitset_test (FDERIVES (i), j))
  96           {
  97             short *rhsp;
  98             fprintf (stderr, "\t\t%d:", j - 1);
  99             for (rhsp = &ritem[rules[j].rhs]; *rhsp >= 0; ++rhsp)
 100               fprintf (stderr, " %s", symbols[*rhsp]->tag);
 101             fputc ('\n', stderr);
 102           }
 103     }
 104   fprintf (stderr, "\n\n");
 105 }
 106 \f
 107 /*------------------------------------------------------------------.
 108 | Set FIRSTS to be an NVARS array of NVARS bitsets indicating which |
 109 | items can represent the beginning of the input corresponding to   |
 110 | which other items.                                                |
 111 |                                                                   |
 112 | For example, if some rule expands symbol 5 into the sequence of   |
 113 | symbols 8 3 20, the symbol 8 can be the beginning of the data for |
 114 | symbol 5, so the bit [8 - ntokens] in first[5 - ntokens] (= FIRST |
 115 | (5)) is set.                                                      |
 116 `------------------------------------------------------------------*/
 117
 118 static void
 119 set_firsts (void)
 120 {
 121   int i, j;
 122
 123   firsts = XCALLOC (bitset, nvars);
 124   for (i = ntokens; i < nsyms; i++)
 125     {
 126       FIRSTS (i) = bitset_create (nvars, BITSET_FIXED);
 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
 135   RTC (firsts, nvars);
 136
 137   if (trace_flag)
 138     print_firsts ();
 139 }
 140
 141 /*-------------------------------------------------------------------.
 142 | Set FDERIVES to an NVARS by NRULES matrix of bits indicating which |
 143 | rules can help derive the beginning of the data for each           |
 144 | nonterminal.                                                       |
 145 |                                                                    |
 146 | For example, if symbol 5 can be derived as the sequence of symbols |
 147 | 8 3 20, and one of the rules for deriving symbol 8 is rule 4, then |
 148 | the [5 - NTOKENS, 4] bit in FDERIVES is set.                       |
 149 `-------------------------------------------------------------------*/
 150
 151 static void
 152 set_fderives (void)
 153 {
 154   int i, j, k;
 155
 156   fderives = XCALLOC (bitset, nvars);
 157   bitset_stats_init ();
 158   for (i = 0 ; i < nvars; ++i)
 159     fderives[i] = bitset_create (nrules + 1, BITSET_FIXED);
 160
 161   set_firsts ();
 162
 163   for (i = ntokens; i < nsyms; ++i)
 164     for (j = ntokens; j < nsyms; ++j)
 165       if (bitset_test (FIRSTS (i), j - ntokens))
 166         for (k = 0; derives[j][k] > 0; ++k)
 167           bitset_set (FDERIVES (i), derives[j][k]);
 168
 169   if (trace_flag)
 170     print_fderives ();
 171
 172   for (i = ntokens; i < nsyms; ++i)
 173     bitset_free (FIRSTS (i));
 174   XFREE (firsts);
 175 }
 176 \f
 177
 178 void
 179 new_closure (int n)
 180 {
 181   itemset = XCALLOC (short, n);
 182
 183   ruleset = bitset_create (nrules + 1, BITSET_FIXED);
 184
 185   set_fderives ();
 186 }
 187
 188
 189
 190 void
 191 closure (short *core, int n)
 192 {
 193   /* Index over CORE. */
 194   int c;
 195
 196   /* An index over RULESET. */
 197   int r;
 198
 199   /* A bit index over RULESET. */
 200   int ruleno;
 201
 202   if (trace_flag)
 203     print_closure ("input", core, n);
 204
 205   if (n == 0)
 206     {
 207       bitset_copy (ruleset, FDERIVES (start_symbol));
 208     }
 209   else
 210     {
 211       bitset_zero (ruleset);
 212
 213       for (c = 0; c < n; ++c)
 214         if (ISVAR (ritem[core[c]]))
 215           bitset_or (ruleset, ruleset, FDERIVES (ritem[core[c]]));
 216     }
 217
 218   nitemset = 0;
 219   c = 0;
 220   for (ruleno = 0; ruleno < nrules + 1; ++ruleno)
 221     if (bitset_test (ruleset, ruleno))
 222       {
 223         int itemno = rules[ruleno].rhs;
 224         while (c < n && core[c] < itemno)
 225           {
 226             itemset[nitemset] = core[c];
 227             nitemset++;
 228             c++;
 229           }
 230         itemset[nitemset] = itemno;
 231         nitemset++;
 232       }
 233
 234   while (c < n)
 235     {
 236       itemset[nitemset] = core[c];
 237       nitemset++;
 238       c++;
 239     }
 240
 241   if (trace_flag)
 242     print_closure ("output", itemset, nitemset);
 243 }
 244
 245
 246 void
 247 free_closure (void)
 248 {
 249   int i;
 250   XFREE (itemset);
 251
 252   bitset_free (ruleset);
 253
 254   for (i = 0 ; i < nvars; ++i)
 255     bitset_free (fderives[i]);
 256   free (fderives);
 257 }