/* Compute look-ahead criteria for bison,
   Copyright (C) 1984, 1986, 1989, 2000, 2001, 2002
   Free Software Foundation, Inc.

   This file is part of Bison, the GNU Compiler Compiler.

   Bison is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   Bison is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with Bison; see the file COPYING.  If not, write to
   the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */


/* Compute how to make the finite state machine deterministic; find
   which rules need lookahead in each state, and which lookahead
   tokens they accept.  */

#include "system.h"
#include "bitset.h"
#include "bitsetv.h"
#include "relation.h"
#include "quotearg.h"
#include "symtab.h"
#include "gram.h"
#include "reader.h"
#include "types.h"
#include "LR0.h"
#include "complain.h"
#include "lalr.h"
#include "nullable.h"
#include "derives.h"
#include "getargs.h"

rule_t **LArule = NULL;
bitsetv LA = NULL;
size_t nLA;

static int ngotos;
short *goto_map = NULL;
state_number_t *from_state = NULL;
state_number_t *to_state = NULL;

/* And for the famous F variable, which name is so descriptive that a
   comment is hardly needed.  <grin>.  */
static bitsetv F = NULL;

static short **includes;
static shorts **lookback;




static void
initialize_LA (void)
{
  state_number_t i;
  int j;
  rule_t **np;

  /* Avoid having to special case 0.  */
  if (!nLA)
    nLA = 1;

  LA = bitsetv_create (nLA, ntokens, BITSET_FIXED);
  LArule = XCALLOC (rule_t *, nLA);
  lookback = XCALLOC (shorts *, nLA);

  np = LArule;
  for (i = 0; i < nstates; i++)
    if (!states[i]->consistent)
      for (j = 0; j < states[i]->reductions->num; j++)
	*np++ = &rules[states[i]->reductions->rules[j]];
}


static void
set_goto_map (void)
{
  state_number_t state;
  short *temp_map;

  goto_map = XCALLOC (short, nvars + 1) - ntokens;
  temp_map = XCALLOC (short, nvars + 1) - ntokens;

  ngotos = 0;
  for (state = 0; state < nstates; ++state)
    {
      transitions_t *sp = states[state]->transitions;
      int i;
      for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
	{
	  if (ngotos == SHRT_MAX)
	    fatal (_("too many gotos (max %d)"), SHRT_MAX);

	  ngotos++;
	  goto_map[TRANSITION_SYMBOL (sp, i)]++;
	}
    }

  {
    int k = 0;
    int i;
    for (i = ntokens; i < nsyms; i++)
      {
	temp_map[i] = k;
	k += goto_map[i];
      }

    for (i = ntokens; i < nsyms; i++)
      goto_map[i] = temp_map[i];

    goto_map[nsyms] = ngotos;
    temp_map[nsyms] = ngotos;
  }

  from_state = XCALLOC (state_number_t, ngotos);
  to_state = XCALLOC (state_number_t, ngotos);

  for (state = 0; state < nstates; ++state)
    {
      transitions_t *sp = states[state]->transitions;
      int i;
      for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
	{
	  int k = temp_map[TRANSITION_SYMBOL (sp, i)]++;
	  from_state[k] = state;
	  to_state[k] = sp->states[i];
	}
    }

  XFREE (temp_map + ntokens);
}



/*----------------------------------------------------------.
| Map a state/symbol pair into its numeric representation.  |
`----------------------------------------------------------*/

static int
map_goto (state_number_t state, symbol_number_t symbol)
{
  int high;
  int low;
  int middle;
  state_number_t s;

  low = goto_map[symbol];
  high = goto_map[symbol + 1] - 1;

  while (low <= high)
    {
      middle = (low + high) / 2;
      s = from_state[middle];
      if (s == state)
	return middle;
      else if (s < state)
	low = middle + 1;
      else
	high = middle - 1;
    }

  assert (0);
  /* NOTREACHED */
  return 0;
}


static void
initialize_F (void)
{
  short **reads = XCALLOC (short *, ngotos);
  short *edge = XCALLOC (short, ngotos + 1);
  int nedges = 0;

  int i;

  F = bitsetv_create (ngotos, ntokens, BITSET_FIXED);

  for (i = 0; i < ngotos; i++)
    {
      state_number_t stateno = to_state[i];
      transitions_t *sp = states[stateno]->transitions;

      int j;
      for (j = 0; j < sp->num && TRANSITION_IS_SHIFT (sp, j); j++)
	bitset_set (F[i], TRANSITION_SYMBOL (sp, j));

      for (; j < sp->num; j++)
	{
	  symbol_number_t symbol = TRANSITION_SYMBOL (sp, j);
	  if (nullable[symbol])
	    edge[nedges++] = map_goto (stateno, symbol);
	}

      if (nedges)
	{
	  reads[i] = XCALLOC (short, nedges + 1);
	  memcpy (reads[i], edge, nedges * sizeof (edge[0]));
	  reads[i][nedges] = -1;
	  nedges = 0;
	}
    }

  relation_digraph (reads, ngotos, &F);

  for (i = 0; i < ngotos; i++)
    XFREE (reads[i]);

  XFREE (reads);
  XFREE (edge);
}


static void
add_lookback_edge (state_t *state, rule_number_t ruleno, int gotono)
{
  int i;
  shorts *sp;

  for (i = 0; i < state->nlookaheads; ++i)
    if (state->lookaheads_rule[i]->number == ruleno)
      break;

  assert (state->lookaheads_rule[i]->number == ruleno);

  sp = XCALLOC (shorts, 1);
  sp->next = lookback[(state->lookaheads - LA) + i];
  sp->value = gotono;
  lookback[(state->lookaheads - LA) + i] = sp;
}



static void
build_relations (void)
{
  short *edge = XCALLOC (short, ngotos + 1);
  state_number_t *states1 = XCALLOC (state_number_t, ritem_longest_rhs () + 1);
  int i;

  includes = XCALLOC (short *, ngotos);

  for (i = 0; i < ngotos; i++)
    {
      int nedges = 0;
      symbol_number_t symbol1 = states[to_state[i]]->accessing_symbol;
      rule_number_t *rulep;

      for (rulep = derives[symbol1]; *rulep > 0; rulep++)
	{
	  int done;
	  int length = 1;
	  item_number_t *rp;
	  state_t *state = states[from_state[i]];
	  states1[0] = state->number;

	  for (rp = rules[*rulep].rhs; *rp >= 0; rp++)
	    {
	      state = transitions_to (state->transitions,
				      item_number_as_symbol_number (*rp));
	      states1[length++] = state->number;
	    }

	  if (!state->consistent)
	    add_lookback_edge (state, *rulep, i);

	  length--;
	  done = 0;
	  while (!done)
	    {
	      done = 1;
	      rp--;
	      /* JF added rp>=ritem &&   I hope to god its right! */
	      if (rp >= ritem && ISVAR (*rp))
		{
		  /* Downcasting from item_number_t to symbol_number_t. */
		  edge[nedges++] = map_goto (states1[--length],
					     item_number_as_symbol_number (*rp));
		  if (nullable[*rp])
		    done = 0;
		}
	    }
	}

      if (nedges)
	{
	  int j;
	  includes[i] = XCALLOC (short, nedges + 1);
	  for (j = 0; j < nedges; j++)
	    includes[i][j] = edge[j];
	  includes[i][nedges] = -1;
	}
    }

  XFREE (edge);
  XFREE (states1);

  relation_transpose (&includes, ngotos);
}



static void
compute_FOLLOWS (void)
{
  int i;

  relation_digraph (includes, ngotos, &F);

  for (i = 0; i < ngotos; i++)
    XFREE (includes[i]);

  XFREE (includes);
}


static void
compute_lookaheads (void)
{
  size_t i;
  shorts *sp;

  for (i = 0; i < nLA; i++)
    for (sp = lookback[i]; sp; sp = sp->next)
      bitset_or (LA[i], LA[i], F[sp->value]);

  /* Free LOOKBACK. */
  for (i = 0; i < nLA; i++)
    LIST_FREE (shorts, lookback[i]);

  XFREE (lookback);
  bitsetv_free (F);
}


/*-------------------------------------------------------------.
| Count the number of lookaheads required for each state       |
| (NLOOKAHEADS member).  Compute the total number of LA, NLA.  |
`-------------------------------------------------------------*/

static void
states_lookaheads_count (void)
{
  state_number_t i;
  nLA = 0;

  /* Count   */
  for (i = 0; i < nstates; i++)
    {
      int k;
      int nlookaheads = 0;
      reductions_t *rp = states[i]->reductions;
      transitions_t *sp = states[i]->transitions;

      /* We need a lookahead either to distinguish different
	 reductions (i.e., there are two or more), or to distinguish a
	 reduction from a shift.  Otherwise, it is straightforward,
	 and the state is `consistent'.  */
      if (rp->num > 1
	  || (rp->num == 1 && sp->num && TRANSITION_IS_SHIFT (sp, 0)))
	nlookaheads += rp->num;
      else
	states[i]->consistent = 1;

      for (k = 0; k < sp->num; k++)
	if (TRANSITION_IS_ERROR (sp, k))
	  {
	    states[i]->consistent = 0;
	    break;
	  }

      states[i]->nlookaheads = nlookaheads;
      nLA += nlookaheads;
    }
}


/*--------------------------------------.
| Initializing the lookaheads members.  |
`--------------------------------------*/

static void
states_lookaheads_initialize (void)
{
  state_number_t i;
  bitsetv pLA = LA;
  rule_t **pLArule = LArule;

  /* Initialize the members LOOKAHEADS and LOOKAHEADS_RULE for each
     state.  */
  for (i = 0; i < nstates; i++)
    {
      states[i]->lookaheads = pLA;
      states[i]->lookaheads_rule = pLArule;
      pLA += states[i]->nlookaheads;
      pLArule += states[i]->nlookaheads;
    }
}


/*---------------------------------------.
| Output the lookaheads for each state.  |
`---------------------------------------*/

static void
lookaheads_print (FILE *out)
{
  state_number_t i;
  int j, k;
  fprintf (out, "Lookaheads: BEGIN\n");
  for (i = 0; i < nstates; ++i)
    {
      bitset_iterator iter;

      fprintf (out, "State %d: %d lookaheads\n",
	       i, states[i]->nlookaheads);

      for (j = 0; j < states[i]->nlookaheads; ++j)
	BITSET_FOR_EACH (iter, states[i]->lookaheads[j], k, 0)
	{
	  fprintf (out, "   on %d (%s) -> rule %d\n",
		   k, symbols[k]->tag,
		   states[i]->lookaheads_rule[j]->number - 1);
	};
    }
  fprintf (out, "Lookaheads: END\n");
}

void
lalr (void)
{
  states_lookaheads_count ();
  initialize_LA ();
  states_lookaheads_initialize ();
  set_goto_map ();
  initialize_F ();
  build_relations ();
  compute_FOLLOWS ();
  compute_lookaheads ();

  if (trace_flag)
    lookaheads_print (stderr);
}