cpython/Parser/acceler.c

/***********************************************************
Copyright 1991, 1992 by Stichting Mathematisch Centrum, Amsterdam, The
Netherlands.

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STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

******************************************************************/

/* Parser accelerator module */

/* The parser as originally conceived had disappointing performance.
   This module does some precomputation that speeds up the selection
   of a DFA based upon a token, turning a search through an array
   into a simple indexing operation.  The parser now cannot work
   without the accelerators installed.  Note that the accelerators
   are installed dynamically when the parser is initialized, they
   are not part of the static data structure written on graminit.[ch]
   by the parser generator. */

#include "pgenheaders.h"
#include "grammar.h"
#include "token.h"
#include "parser.h"

/* Forward references */
static void fixdfa PROTO((grammar *, dfa *));
static void fixstate PROTO((grammar *, state *));

void
addaccelerators(g)
	grammar *g;
{
	dfa *d;
	int i;
#ifdef DEBUG
	fprintf(stderr, "Adding parser accelerators ...\n");
#endif
	d = g->g_dfa;
	for (i = g->g_ndfas; --i >= 0; d++)
		fixdfa(g, d);
	g->g_accel = 1;
#ifdef DEBUG
	fprintf(stderr, "Done.\n");
#endif
}

static void
fixdfa(g, d)
	grammar *g;
	dfa *d;
{
	state *s;
	int j;
	s = d->d_state;
	for (j = 0; j < d->d_nstates; j++, s++)
		fixstate(g, s);
}

static void
fixstate(g, s)
	grammar *g;
	state *s;
{
	arc *a;
	int k;
	int *accel;
	int nl = g->g_ll.ll_nlabels;
	s->s_accept = 0;
	accel = NEW(int, nl);
	for (k = 0; k < nl; k++)
		accel[k] = -1;
	a = s->s_arc;
	for (k = s->s_narcs; --k >= 0; a++) {
		int lbl = a->a_lbl;
		label *l = &g->g_ll.ll_label[lbl];
		int type = l->lb_type;
		if (a->a_arrow >= (1 << 7)) {
			printf("XXX too many states!\n");
			continue;
		}
		if (ISNONTERMINAL(type)) {
			dfa *d1 = finddfa(g, type);
			int ibit;
			if (type - NT_OFFSET >= (1 << 7)) {
				printf("XXX too high nonterminal number!\n");
				continue;
			}
			for (ibit = 0; ibit < g->g_ll.ll_nlabels; ibit++) {
				if (testbit(d1->d_first, ibit)) {
#ifdef applec
#define MPW_881_bug			/* Undefine if bug below is fixed */
#endif
#ifdef MPW_881_BUG
					/* In 881 mode MPW 3.1 has a code
					   generation bug which seems to
					   set the upper bits; fix this by
					   explicitly masking them off */
					int temp;
#endif
					if (accel[ibit] != -1)
						printf("XXX ambiguity!\n");
#ifdef MPW_881_BUG
					temp = 0xFFFF &
						(a->a_arrow | (1 << 7) |
						 ((type - NT_OFFSET) << 8));
					accel[ibit] = temp;
#else
					accel[ibit] = a->a_arrow | (1 << 7) |
						((type - NT_OFFSET) << 8);
#endif
				}
			}
		}
		else if (lbl == EMPTY)
			s->s_accept = 1;
		else if (lbl >= 0 && lbl < nl)
			accel[lbl] = a->a_arrow;
	}
	while (nl > 0 && accel[nl-1] == -1)
		nl--;
	for (k = 0; k < nl && accel[k] == -1;)
		k++;
	if (k < nl) {
		int i;
		s->s_accel = NEW(int, nl-k);
		if (s->s_accel == NULL) {
			fprintf(stderr, "no mem to add parser accelerators\n");
			exit(1);
		}
		s->s_lower = k;
		s->s_upper = nl;
		for (i = 0; k < nl; i++, k++)
			s->s_accel[i] = accel[k];
	}
	DEL(accel);
}