1 files changed, 109 insertions, 0 deletions
diff --git a/Parser/firstsets.c b/Parser/firstsets.c
new file mode 100644
index 0000000..0f28dd0
--- /dev/null
+++ b/Parser/firstsets.c
@@ -0,0 +1,109 @@
+/* Computation of FIRST stets */
+
+#include <stdio.h>
+
+#include "PROTO.h"
+#include "malloc.h"
+#include "grammar.h"
+#include "token.h"
+
+extern int debugging;
+
+static void
+calcfirstset(g, d)
+	grammar *g;
+	dfa *d;
+{
+	int i, j;
+	state *s;
+	arc *a;
+	int nsyms;
+	int *sym;
+	int nbits;
+	static bitset dummy;
+	bitset result;
+	int type;
+	dfa *d1;
+	label *l0;
+	
+	if (debugging)
+		printf("Calculate FIRST set for '%s'\n", d->d_name);
+	
+	if (dummy == NULL)
+		dummy = newbitset(1);
+	if (d->d_first == dummy) {
+		fprintf(stderr, "Left-recursion for '%s'\n", d->d_name);
+		return;
+	}
+	if (d->d_first != NULL) {
+		fprintf(stderr, "Re-calculating FIRST set for '%s' ???\n",
+			d->d_name);
+	}
+	d->d_first = dummy;
+	
+	l0 = g->g_ll.ll_label;
+	nbits = g->g_ll.ll_nlabels;
+	result = newbitset(nbits);
+	
+	sym = NEW(int, 1);
+	if (sym == NULL)
+		fatal("no mem for new sym in calcfirstset");
+	nsyms = 1;
+	sym[0] = findlabel(&g->g_ll, d->d_type, (char *)NULL);
+	
+	s = &d->d_state[d->d_initial];
+	for (i = 0; i < s->s_narcs; i++) {
+		a = &s->s_arc[i];
+		for (j = 0; j < nsyms; j++) {
+			if (sym[j] == a->a_lbl)
+				break;
+		}
+		if (j >= nsyms) { /* New label */
+			RESIZE(sym, int, nsyms + 1);
+			if (sym == NULL)
+				fatal("no mem to resize sym in calcfirstset");
+			sym[nsyms++] = a->a_lbl;
+			type = l0[a->a_lbl].lb_type;
+			if (ISNONTERMINAL(type)) {
+				d1 = finddfa(g, type);
+				if (d1->d_first == dummy) {
+					fprintf(stderr,
+						"Left-recursion below '%s'\n",
+						d->d_name);
+				}
+				else {
+					if (d1->d_first == NULL)
+						calcfirstset(g, d1);
+					mergebitset(result, d1->d_first, nbits);
+				}
+			}
+			else if (ISTERMINAL(type)) {
+				addbit(result, a->a_lbl);
+			}
+		}
+	}
+	d->d_first = result;
+	if (debugging) {
+		printf("FIRST set for '%s': {", d->d_name);
+		for (i = 0; i < nbits; i++) {
+			if (testbit(result, i))
+				printf(" %s", labelrepr(&l0[i]));
+		}
+		printf(" }\n");
+	}
+}
+
+void
+addfirstsets(g)
+	grammar *g;
+{
+	int i;
+	dfa *d;
+	
+	printf("Adding FIRST sets ...\n");
+	for (i = 0; i < g->g_ndfas; i++) {
+		d = &g->g_dfa[i];
+		if (d->d_first == NULL)
+			calcfirstset(g, d);
+	}
+}