Parser/firstsets.c

   1 /***********************************************************
   2 Copyright 1991, 1992, 1993, 1994 by Stichting Mathematisch Centrum,
   3 Amsterdam, The Netherlands.
   4
   5                         All Rights Reserved
   6
   7 Permission to use, copy, modify, and distribute this software and its
   8 documentation for any purpose and without fee is hereby granted,
   9 provided that the above copyright notice appear in all copies and that
  10 both that copyright notice and this permission notice appear in
  11 supporting documentation, and that the names of Stichting Mathematisch
  12 Centrum or CWI not be used in advertising or publicity pertaining to
  13 distribution of the software without specific, written prior permission.
  14
  15 STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
  16 THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
  17 FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE
  18 FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  19 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  20 ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  21 OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  22
  23 ******************************************************************/
  24
  25 /* Computation of FIRST stets */
  26
  27 #include "pgenheaders.h"
  28 #include "grammar.h"
  29 #include "token.h"
  30
  31 extern int debugging;
  32
  33 /* Forward */
  34 static void calcfirstset PROTO((grammar *, dfa *));
  35
  36 void
  37 addfirstsets(g)
  38         grammar *g;
  39 {
  40         int i;
  41         dfa *d;
  42
  43         printf("Adding FIRST sets ...\n");
  44         for (i = 0; i < g->g_ndfas; i++) {
  45                 d = &g->g_dfa[i];
  46                 if (d->d_first == NULL)
  47                         calcfirstset(g, d);
  48         }
  49 }
  50
  51 static void
  52 calcfirstset(g, d)
  53         grammar *g;
  54         dfa *d;
  55 {
  56         int i, j;
  57         state *s;
  58         arc *a;
  59         int nsyms;
  60         int *sym;
  61         int nbits;
  62         static bitset dummy;
  63         bitset result;
  64         int type;
  65         dfa *d1;
  66         label *l0;
  67
  68         if (debugging)
  69                 printf("Calculate FIRST set for '%s'\n", d->d_name);
  70
  71         if (dummy == NULL)
  72                 dummy = newbitset(1);
  73         if (d->d_first == dummy) {
  74                 fprintf(stderr, "Left-recursion for '%s'\n", d->d_name);
  75                 return;
  76         }
  77         if (d->d_first != NULL) {
  78                 fprintf(stderr, "Re-calculating FIRST set for '%s' ???\n",
  79                         d->d_name);
  80         }
  81         d->d_first = dummy;
  82
  83         l0 = g->g_ll.ll_label;
  84         nbits = g->g_ll.ll_nlabels;
  85         result = newbitset(nbits);
  86
  87         sym = NEW(int, 1);
  88         if (sym == NULL)
  89                 fatal("no mem for new sym in calcfirstset");
  90         nsyms = 1;
  91         sym[0] = findlabel(&g->g_ll, d->d_type, (char *)NULL);
  92
  93         s = &d->d_state[d->d_initial];
  94         for (i = 0; i < s->s_narcs; i++) {
  95                 a = &s->s_arc[i];
  96                 for (j = 0; j < nsyms; j++) {
  97                         if (sym[j] == a->a_lbl)
  98                                 break;
  99                 }
 100                 if (j >= nsyms) { /* New label */
 101                         RESIZE(sym, int, nsyms + 1);
 102                         if (sym == NULL)
 103                                 fatal("no mem to resize sym in calcfirstset");
 104                         sym[nsyms++] = a->a_lbl;
 105                         type = l0[a->a_lbl].lb_type;
 106                         if (ISNONTERMINAL(type)) {
 107                                 d1 = finddfa(g, type);
 108                                 if (d1->d_first == dummy) {
 109                                         fprintf(stderr,
 110                                                 "Left-recursion below '%s'\n",
 111                                                 d->d_name);
 112                                 }
 113                                 else {
 114                                         if (d1->d_first == NULL)
 115                                                 calcfirstset(g, d1);
 116                                         mergebitset(result, d1->d_first, nbits);
 117                                 }
 118                         }
 119                         else if (ISTERMINAL(type)) {
 120                                 addbit(result, a->a_lbl);
 121                         }
 122                 }
 123         }
 124         d->d_first = result;
 125         if (debugging) {
 126                 printf("FIRST set for '%s': {", d->d_name);
 127                 for (i = 0; i < nbits; i++) {
 128                         if (testbit(result, i))
 129                                 printf(" %s", labelrepr(&l0[i]));
 130                 }
 131                 printf(" }\n");
 132         }
 133 }