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/*

 * Copyright (c) 2002-2005 The TenDRA Project <http://www.tendra.org/>.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 * 1. Redistributions of source code must retain the above copyright notice,

 *    this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright notice,

 *    this list of conditions and the following disclaimer in the documentation

 *    and/or other materials provided with the distribution.

 * 3. Neither the name of The TenDRA Project nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific, prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS

 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR

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 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 *

 * $Id$

 */

/*

    		 Crown Copyright (c) 1997

    This TenDRA(r) Computer Program is subject to Copyright

    owned by the United Kingdom Secretary of State for Defence

    acting through the Defence Evaluation and Research Agency

    (DERA).  It is made available to Recipients with a

    royalty-free licence for its use, reproduction, transfer

    to other parties and amendment for any purpose not excluding

    product development provided that any such use et cetera

    shall be deemed to be acceptance of the following conditions:-

        (1) Its Recipients shall ensure that this Notice is

        reproduced upon any copies or amended versions of it;

        (2) Any amended version of it shall be clearly marked to

        show both the nature of and the organisation responsible

        for the relevant amendment or amendments;

        (3) Its onward transfer from a recipient to another

        party shall be deemed to be that party's acceptance of

        these conditions;

        (4) DERA gives no warranty or assurance as to its

        quality or suitability for any purpose and DERA accepts

        no liability whatsoever in relation to any use to which

        it may be put.

*/

/*** rule-factor.c --- Factorisation of rules.

 *

 ** Author: Steve Folkes <smf@hermes.mod.uk>

 *

 *** Commentary:

 *

 * This file implements the SID factorisation routines.

 *

 * The factorisation process consists of the following phases:

 *

 * 1. The rule is reordered so that alternatives with the same initial item

 * are grouped together, for example the rule:

 *

 * 	A = x A,

 * 	    x B,

 * 	    y A,

 * 	    z A,

 * 	    y B;

 *

 * would be reordered to:

 *

 * 	A = x A,

 * 	    x B,

 * 	    y A,

 * 	    y B,

 * 	    z A;

 *

 * and three groups would have been created:

 *

 * 	x A, x B

 *

 * 	y A, y B

 *

 * 	z A

 *

 * Each group has its first set calculated (this is the union of the first

 * sets of each of the alternatives in the group), and its priority.  The

 * priority of a group is one more than the priority of the rule with the

 * highest priority in any of the group's alternatives, which is not preceded

 * by an action.  If there is no such rule, then the group's priority is one.

 *

 * The ``rule_group_by_initial_item'' function is responsible for this

 * re-ordering.  It uses the rule's alternative tail pointer (``alt_tail'') to

 * indicate where in the rule it should start the grouping from.  Nothing

 * before this point is modified (it is assumed that it is already grouped).

 * The pointer will always be restored to the end of the alternative list by

 * the time this function returns.

 *

 * 2. Having split the rule up into groups, it then looks at each group to see

 * if there are alternatives of the form:

 *

 * 	B C ...

 *

 * where "B" is a see through rule, and the first set of "B" contains some

 * terminals from the first set of "C ...".  If it finds any, it removes the

 * group from the rule, and expands "B" in all alternatives in the group,

 * putting the new alternatives at the end of the rule.  It also looks for

 * alternatives that begin with a rule which has a predicate in its first set,

 * in which case it also expands the rule in all alternatives in the group.

 * It then recomputes the groups for the new alternatives, and tries again.

 * This phase and the next phase are implemented by the function

 * ``rule_expand_item_clashes''.  It is not possible to expand a rule that has

 * an exception handler into another rule that has an exception handler

 * (unless the exception handlers are identical).

 *

 * 3. The next phase is to check to see if any of the groups have common

 * terminals in their first sets.  If this is the case (and the first item in

 * each alternative in at least one of the groups is a rule), then the group

 * with the highest priority is removed from the rule, and the first item is

 * expanded in all alternatives in the group, putting the new alternatives at

 * the end of the rule.  It then recalculates the groups for the new

 * alternatives, and tries again.

 *

 * 4. The last stage is to change a group of the form:

 *

 * 	  B C

 * 	| B D

 *

 * into

 *

 * 	  B X

 *

 * 	X = C

 * 	  | D

 *

 * where "X" is a newly created rule.  The algorithm actually removes all

 * initial items that are the same for all members of the group.  It also

 * performs renaming of the result names of the final item in the group of

 * identical items if necessary.

 *

 * It is possible that this final stage of the factorization process will go

 * on forever.  To prevent this, there is a limit on the number of new rules

 * that can be created.  This stage of the factorisation process is

 * implemented by the functions ``rule_factor_2'', ``rule_factor_3'', and

 * ``rule_factor_4''.

 *

 * When the new rule is created, the ``rule_compute_first_set_1'' function is

 * called to calculate its first set, whether or not it is see through and its

 * priority.  The new rules are created untraced, to ensure that the

 * factorisation process will be applied to them as well.

 *

 *** Change Log:

 * $Log: rule-factor.c,v $

 * Revision 1.1.1.1  1998/01/17  15:57:46  release

 * First version to be checked into rolling release.

 *

 * Revision 1.2  1994/12/15  09:58:37  smf

 * Brought into line with OSSG C Coding Standards Document, as per

 * "CR94_178.sid+tld-update".

 *

 * Revision 1.1.1.1  1994/07/25  16:04:38  smf

 * Initial import of SID 1.8 non shared files.

 *

**/

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

#include "rule.h"

#include "basic.h"

#include "bitvec.h"

#include "entry-list.h"

#include "gen-errors.h"

#include "types.h"

/*--------------------------------------------------------------------------*/

typedef struct AltGroupT {

    struct AltGroupT	       *next;

    BitVecT			first_set;

    EntryListT			predicate_first;

    unsigned			priority;

    AltP		       *alt_ref;

} AltGroupT, *AltGroupP;

typedef struct AltGroupListT {

    AltGroupP			head;

    AltGroupP		       *tail;

} AltGroupListT, *AltGroupListP;

/*--------------------------------------------------------------------------*/

static unsigned			rule_factor_limit = 1000;

/*--------------------------------------------------------------------------*/

static unsigned			rule_overlaps(ItemP, BitVecP, EntryListP);

static AltGroupP

group_create(ItemP item, AltP *alt_ref)

{

    AltGroupP group = ALLOCATE(AltGroupT);

    group->next     = NIL(AltGroupP);

    bitvec_init(&(group->first_set));

    entry_list_init(&(group->predicate_first));

    group->priority = rule_overlaps(item, &(group->first_set),

				    &(group->predicate_first));

    group->alt_ref  = alt_ref;

    return(group);

}

static AltGroupP

group_deallocate(AltGroupP group)

{

    AltGroupP next = group->next;

    bitvec_destroy(&(group->first_set));

    entry_list_destroy(&(group->predicate_first));

    DEALLOCATE(group);

    return(next);

}

/*--------------------------------------------------------------------------*/

static unsigned

rule_overlaps(ItemP initial_item, BitVecP first_set, EntryListP predicate_first)

{

    unsigned priority    = 0;

    BoolT    see_through = TRUE;

    BoolT    no_action   = TRUE;

    ItemP    item;

    for (item = initial_item; see_through && (item != NIL(ItemP));

	 item = item_next(item)) {

	switch (item_type(item))EXHAUSTIVE {

	  case ET_PREDICATE:

	    ASSERT(item == initial_item);

	    entry_list_add_if_missing(predicate_first, item_entry(item));

	    see_through = FALSE;

	    break;

	  case ET_RENAME:

	  case ET_ACTION:

	    no_action = FALSE;

	    break;

	  case ET_RULE: {

	      EntryP   entry         = item_entry(item);

	      RuleP    item_rule     = entry_get_rule(entry);

	      unsigned item_priority = rule_get_priority(item_rule);

	      bitvec_or(first_set, rule_first_set(item_rule));

	      entry_list_append(predicate_first,

				rule_predicate_first(item_rule));

	      see_through = rule_is_see_through(item_rule);

	      if ((item_priority > priority) && no_action) {

		  priority = item_priority;

	      }

	  }

	    break;

	  case ET_BASIC: {

	      BasicP basic = entry_get_basic(item_entry(item));

	      see_through = FALSE;

	      bitvec_set(first_set, basic_terminal(basic));

	  }

	    break;

	  case ET_NON_LOCAL:

	  case ET_NAME:

	  case ET_TYPE:

	    UNREACHED;

	}

    }

    return(priority + 1);

}

static void

rule_group_by_initial_item(RuleP rule, AltGroupListP groups)

{

    AltP *alt_ref = (rule->alt_tail);

    AltP  alt;

  next_alt:

    while ((alt = *alt_ref) != NIL(AltP)) {

	ItemP     item = alt_item_head(alt);

	AltGroupP group;

	for (group = groups->head; group; group = group->next) {

	    AltP *group_alt_ref = group->alt_ref;

	    ItemP alt_item      = alt_item_head(*group_alt_ref);

	    if (((item_entry(item) == item_entry(alt_item)) &&

		 types_equal_numbers(item_param(item), item_param(alt_item)) &&

		 types_equal_numbers(item_result(item),

				     item_result(alt_item))) ||

		(item_is_rename(item) && item_is_rename(alt_item) &&

		 types_equal_names(item_param(item), item_param(alt_item)) &&

		 types_equal_names(item_result(item),

				   item_result(alt_item)))) {

		unsigned priority;

		*alt_ref        = alt_next(alt);

		alt_set_next(alt, *group_alt_ref);

		*group_alt_ref  = alt;

		priority        = rule_overlaps(item, &(group->first_set),

						&(group->predicate_first));

		if (priority > group->priority) {

		    group->priority = priority;

		}

		goto next_alt;

	    }

	}

	group           = group_create(item, alt_ref);

	*(groups->tail) = group;

	groups->tail    = &(group->next);

	alt_ref         = alt_next_ref(alt);

    }

    rule->alt_tail = alt_ref;

}

static void			rule_factor_1(RuleP, FactorClosureP);

static void

rule_expand(RuleP rule, FactorClosureP closure, AltGroupP group,

	    AltGroupListP groups)

{

    AltP       alt       = (*(group->alt_ref));

    ItemP      item      = alt_item_head(alt);

    RuleP      item_rule = entry_get_rule(item_entry(item));

    AltP       handler   = rule_get_handler(item_rule);

    AltGroupP *last;

    AltP      *tail;

    TypeTransT translator;

    rule_factor_1(item_rule, closure);

    if (handler && (!alt_equal(handler, rule_get_handler(rule)))) {

	E_factor_handler_mismatch(item_rule, rule);

    }

    if (!non_local_list_is_empty(rule_non_locals(item_rule))) {

	E_factor_nl_entry(item_rule, rule);

    }

    for (last = &(groups->head); *last != group; last = &((*last)->next)) {

	/*NOTHING*/

    }

    if (((*last) = (group->next)) != NIL(AltGroupP)) {

	*(group->alt_ref)      = *(group->next->alt_ref);

	*(group->next->alt_ref) = NIL(AltP);

	group->next->alt_ref    = group->alt_ref;

    } else {

	groups->tail            = last;

	*(group->alt_ref)      = NIL(AltP);

	rule->alt_tail          = group->alt_ref;

    }

   (void)group_deallocate(group);

    tail = rule->alt_tail;

    while (alt) {

	AltP       item_alt = rule_alt_head(item_rule);

	SaveTransT state;

	trans_init(&translator, rule_param(rule), rule_result(rule), alt);

	trans_add_translations(&translator, rule_param(item_rule),

			       item_param(alt_item_head(alt)));

	trans_add_translations(&translator, rule_result(item_rule),

			       item_result(alt_item_head(alt)));

	trans_save_state(&translator, &state);

	if (rule_has_empty_alt(item_rule)) {

	    AltP new_alt = alt_create_merge(NIL(ItemP),

					    item_next(alt_item_head(alt)),

					    &translator, closure->table);

	    *tail = new_alt;

	    tail  = alt_next_ref(new_alt);

	    trans_restore_state(&translator, &state);

	}

	for (; item_alt; item_alt = alt_next(item_alt)) {

	    AltP new_alt = alt_create_merge(alt_item_head(item_alt),

					    item_next(alt_item_head(alt)),

					    &translator, closure->table);

	    *tail = new_alt;

	    tail  = alt_next_ref(new_alt);

	    trans_restore_state(&translator, &state);

	}

	trans_destroy(&translator);

	alt = alt_deallocate(alt);

    }

}

static BoolT

rule_expand_item_clashes(RuleP rule, FactorClosureP closure,

			 AltGroupListP groups)

{

    BitVecP   bitvec1 = &(closure->bitvec1);

    BitVecP   bitvec2 = &(closure->bitvec2);

    AltGroupP group;

    for (group = groups->head; group; group = group->next) {

	AltGroupP group2;

	AltP      first_alt = (*(group->alt_ref));

	ItemP     item      = alt_item_head(first_alt);

	if (item_is_rule(item)) {

	    RuleP item_rule = entry_get_rule(item_entry(item));

	    if (!entry_list_is_empty(rule_predicate_first(item_rule))) {

		rule_expand(rule, closure, group, groups);

		return(TRUE);

	    } else if (rule_is_see_through(item_rule)) {

		AltP       alt = first_alt;

		AltP       end = NIL(AltP);

		EntryListT predicate_first;

		if (group->next) {

		    end = *(group->next->alt_ref);

		}

		bitvec_replace(bitvec1, rule_first_set(item_rule));

		do {

		    bitvec_empty(bitvec2);

		    entry_list_init(&predicate_first);

		   (void)rule_overlaps(item_next(alt_item_head(alt)),

				       bitvec2, &predicate_first);

		    if (bitvec_intersects(bitvec1, bitvec2) ||

			(!entry_list_is_empty(&predicate_first))) {

			entry_list_destroy(&predicate_first);

			rule_expand(rule, closure, group, groups);

			return(TRUE);

		    }

		    entry_list_destroy(&predicate_first);

		} while ((alt = alt_next(alt)) != end);

	    }

	    for (group2 = groups->head; group2; group2 = group2->next) {

		if ((group2 != group) &&

		   (bitvec_intersects(&(group2->first_set),

				      &(group->first_set)))) {

		    if (group->priority > group2->priority) {

			rule_expand(rule, closure, group, groups);

		    } else {

			rule_expand(rule, closure, group2, groups);

		    }

		    return(TRUE);

		}

	    }

	}

    }

    return(FALSE);

}

/*--------------------------------------------------------------------------*/

static ItemP

rule_create_factored(TypeTupleP params, TypeTupleP result, AltP alt,

		     TableP table)

{

    static unsigned factorised_rules = 0;

    EntryP          new_entry;

    ItemP           new_item;

    RuleP           new_rule;

    if (factorised_rules == rule_factor_limit) {

	E_too_many_factorisations(rule_factor_limit);

	UNREACHED;

    }

    factorised_rules ++;

    new_entry = table_add_generated_rule(table, FALSE);

    new_rule  = entry_get_rule(new_entry);

    types_copy(rule_param(new_rule), params);

    types_copy(rule_result(new_rule), result);

    while (alt) {

	AltP tmp_alt = alt;

	alt = alt_next(alt);

	alt_set_next(tmp_alt, NIL(AltP));

	if (alt_item_head(tmp_alt)) {

	    rule_add_alt(new_rule, tmp_alt);

	} else {

	    rule_add_empty_alt(new_rule);

	   (void)alt_deallocate(tmp_alt);

	}

    }

    rule_compute_first_set_1(new_rule);

    new_item  = item_create(new_entry);

    types_assign(item_param(new_item), params);

    types_assign(item_result(new_item), result);

    types_make_references(rule_param(new_rule), item_param(new_item));

    return(new_item);

}

static BoolT

rule_factor_4(RuleP rule, AltP old_alt, AltP new_alt, TableP table,

	      EntryP predicate_id, TypeTupleP params, BoolP items_equal_ref)

{

    ItemP       old_item     = alt_item_head(old_alt);

    BoolT       result_equal = TRUE;

    AltP        alt;

    TypeBTransT translator;

    for (alt = alt_next(old_alt); alt; alt = alt_next(alt)) {

	ItemP item = alt_item_head(alt);

	if (((item == NIL(ItemP)) && (old_item != NIL(ItemP))) ||

	    ((item != NIL(ItemP)) && (old_item == NIL(ItemP)))) {

	    *items_equal_ref = FALSE;

	    return(TRUE);

	} else if ((item == NIL(ItemP)) && (old_item == NIL(ItemP))) {

	    /*NOTHING*/

	} else if (((item_entry(old_item) == item_entry(item)) &&

		    types_equal_numbers(item_param(old_item),

					item_param(item)) &&

		    types_equal_numbers(item_result(old_item),

					item_result(item))) ||

		   (item_is_rename(item) && item_is_rename(old_item) &&

		    types_equal_names(item_param(item),

				      item_param(old_item)) &&

		    types_equal_names(item_result(item),

				      item_result(old_item)))) {

	    if (result_equal) {

		result_equal = types_equal_names(item_result(old_item),

						 item_result(item));

	    }

	} else {

	    *items_equal_ref = FALSE;

	    return(TRUE);

	}

    }

    if (old_item == NIL(ItemP)) {

	*items_equal_ref = FALSE;

	return(FALSE);

    }

    btrans_init(&translator);

    for (alt = old_alt; alt; alt = alt_next(alt)) {

	ItemP item = alt_unlink_item_head(alt);

	if (!result_equal) {

	    ItemP new_item;

	    if (alt == old_alt) {

		new_item = btrans_generate_non_pred_names(&translator,

							  item_result(item),

							  rule_result(rule),

							  predicate_id, table);

		types_translate(item_result(item), &translator);

	    } else {

		new_item = btrans_regen_non_pred_names(&translator,

						       item_result(item),

						       rule_result(rule),

						       table);

	    }

	    item_translate_list(alt_item_head(alt), &translator);

	    if (new_item) {

		alt_add_item(alt, new_item);

	    }

	}

	if (alt == old_alt) {

	    types_add_new_names(params, item_result(item), predicate_id);

	    alt_add_item(new_alt, item);

	} else {

	   (void)item_deallocate(item);

	}

    }

    btrans_destroy(&translator);

    return(TRUE);

}

static void

rule_factor_3(RuleP rule, TableP table, EntryP predicate_id, AltP old_alt,

	      AltP new_alt)

{

    BoolT       items_equal = TRUE;

    BoolT       found_items;

    TypeTupleT  params;

    TypeTupleT  result;

    types_copy(&params, rule_param(rule));

    types_copy(&result, rule_result(rule));

    do {

	found_items = rule_factor_4(rule, old_alt, new_alt, table,

				    predicate_id, &params, &items_equal);

    } while (items_equal);

    if (found_items) {

	ItemP new_item;

	types_unlink_used(&result, &params);

	types_unlink_unused(&params, old_alt);

	new_item = rule_create_factored(&params, &result, old_alt, table);

	alt_add_item(new_alt, new_item);

    } else {

	types_destroy(&params);

	while (old_alt) {

	    AltP tmp_alt = old_alt;

	    old_alt = alt_next(old_alt);

	    ASSERT(alt_item_head(tmp_alt) == NIL(ItemP));

	   (void)alt_deallocate(tmp_alt);

	}

    }

}

static void

rule_factor_2(RuleP rule, TableP table, EntryP predicate_id,

	      AltGroupListP groups)

{

    AltGroupP group;

    for (group = groups->head; group; group = group_deallocate(group)) {

	AltP alt = *(group->alt_ref);

	AltP new_alt;

	if (group->next) {

	    if (group->next->alt_ref == alt_next_ref(*(group->alt_ref))) {

		goto done;

	    }

	    new_alt                 = alt_create();

	    alt_set_next(new_alt, *(group->next->alt_ref));

	    *(group->next->alt_ref) = NIL(AltP);

	    group->next->alt_ref    = alt_next_ref(new_alt);

	} else {

	    if (alt_next(*(group->alt_ref)) == NIL(AltP)) {

		goto done;

	    }

	    new_alt        = alt_create();

	    rule->alt_tail = alt_next_ref(new_alt);

	}

	*(group->alt_ref) = new_alt;

	rule_factor_3(rule, table, predicate_id, alt, new_alt);

      done:;

    }

}

static void

rule_factor_1(RuleP rule, FactorClosureP closure)

{

    AltGroupListT groups;

    groups.head = NIL(AltGroupP);

    groups.tail = &(groups.head);

    if (rule_is_factored(rule)) {

	return;

    }

    rule_factored(rule);

    rule->alt_tail = &(rule->alt_head);

    do {

	rule_renumber(rule, FALSE, closure->predicate_id);

	rule_group_by_initial_item(rule, &groups);

    } while (rule_expand_item_clashes(rule, closure, &groups));

    rule_factor_2(rule, closure->table, closure->predicate_id, &groups);

}

/*--------------------------------------------------------------------------*/

void

rule_factor(EntryP entry, GenericP gclosure)

{

    FactorClosureP closure = (FactorClosureP)gclosure;

    if (entry_is_rule(entry)) {

	RuleP rule = entry_get_rule(entry);

	rule_factor_1(rule, closure);

    }

}

void

rule_set_factor_limit(unsigned limit)

{

    rule_factor_limit = limit;

}

/*

 * Local variables(smf):

 * eval: (include::add-path-entry "../os-interface" "../library")

 * eval: (include::add-path-entry "../generated")

 * end:

**/