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/*

    		 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-simp.c --- Rule simplification routines.

 *

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

 *

 *** Commentary:

 *

 * This file implements the SID elimination of identical rules routines.

 *

 * In order to optimise the elimination of identical rules the following is

 * done:

 *

 * 	- name flow through each rule is numbered, so that differences in

 *	  names do not affect the comparisons;

 *

 *	- alternatives are reordered so that they will appear in the same

 *	  order in identical rules;

 *

 *	- rules are placed in a hash table, so that identical rules will be in

 *	  the same slot in the table.

 *

 * The first two of these make comparisons between two rules quicker.  The

 * third reduces the number of comparisons that are made.

 *

 * One important thing to remember is that the hash value of a rule should not

 * depend upon the names of any rules that it calls.  If this was the case,

 * and one of the rules was replaced then it would be possible to have two

 * identical rules in different slots in the hash table!

 *

 * If two identical rules are found, one is substituted for the other.  If

 * one of the rules is a required rule, then it becomes the used rule.

 *

 *** Change Log:

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

 * Revision 1.1.1.1  1998/01/17  15:57:47  release

 * First version to be checked into rolling release.

 *

 * Revision 1.2  1994/12/15  09:58:52  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  16:04:41  smf

 * Initial import of SID 1.8 non shared files.

 *

**/

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

#include "rule.h"

#include "action.h"

#include "basic.h"

#include "entry-list.h"

#include "name.h"

#include "type.h"

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

#define EQUALITY_TABLE_SIZE (127)

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

typedef struct RuleSortListT {

    AltP			head;

    AltP		       *tail;

} RuleSortListT, *RuleSortListP;

typedef struct ReplaceClosureT {

    EntryP			from;

    EntryP			to;

} ReplaceClosureT, *ReplaceClosureP;

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

static RuleP			equality_table [EQUALITY_TABLE_SIZE];

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

static void

rule_sort_alts PROTO_N ((sort_list))

	       PROTO_T (RuleSortListP sort_list)

{

    AltP alt      = sort_list->head;

    AltP scan_alt = alt_next (alt);

    if (scan_alt) {

	RuleSortListT lower;

	RuleSortListT higher;

	lower.tail  = &(lower.head);

	higher.tail = &(higher.head);

	for (; scan_alt; scan_alt = alt_next (scan_alt)) {

	    if (alt_less_than (scan_alt, alt)) {

		*(lower.tail)  = scan_alt;

		lower.tail     = alt_next_ref (scan_alt);

	    } else {

		*(higher.tail) = scan_alt;

		higher.tail    = alt_next_ref (scan_alt);

	    }

	}

	*(lower.tail)  = NIL (AltP);

	*(higher.tail) = NIL (AltP);

	if (lower.head) {

	    rule_sort_alts (&lower);

	    sort_list->head = lower.head;

	    sort_list->tail = lower.tail;

	} else {

	    sort_list->tail = &(sort_list->head);

	}

	*(sort_list->tail) = alt;

	sort_list->tail    = alt_next_ref (alt);

	if (higher.head) {

	    rule_sort_alts (&higher);

	    *(sort_list->tail) = higher.head;

	    sort_list->tail    = higher.tail;

	}

	*(sort_list->tail) = NIL (AltP);

    }

}

static void

rule_reorder PROTO_N ((rule))

	     PROTO_T (RuleP rule)

{

    RuleSortListT sort_list;

    if ((sort_list.head = rule_alt_head (rule)) != NIL (AltP)) {

	sort_list.tail = rule->alt_tail;

	rule_sort_alts (&sort_list);

	rule->alt_head = sort_list.head;

	rule->alt_tail = sort_list.tail;

    }

}

static void

rule_hash_1 PROTO_N ((rule, predicate_id))

	    PROTO_T (RuleP  rule X

		     EntryP predicate_id)

{

    unsigned hash_value = (unsigned) (rule_has_empty_alt (rule) ? 3 : 0);

    AltP     alt;

    rule_renumber (rule, TRUE, predicate_id);

    rule_reorder (rule);

    for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

	ItemP item;

	KeyP  key = NIL (KeyP);

	hash_value += 5;

	for (item = alt_item_head (alt); item; item = item_next (item)) {

	    hash_value ++;

	    if (!item_is_rule (item)) {

		key = entry_key (item_entry (item));

	    }

	}

	if (key) {

	    hash_value += key_hash_value (key);

	}

    }

    hash_value %= EQUALITY_TABLE_SIZE;

    rule_set_next_in_table (rule, equality_table [hash_value]);

    equality_table [hash_value] = rule;

}

static void

rule_hash_for_comparison PROTO_N ((entry, gclosure))

			 PROTO_T (EntryP   entry X

				  GenericP gclosure)

{

    if (entry_is_rule (entry)) {

	RuleP  rule         = entry_get_rule (entry);

	EntryP predicate_id = (EntryP) gclosure;

	rule_hash_1 (rule, predicate_id);

    }

}

static BoolT

rule_equal PROTO_N ((rule1, rule2))

	   PROTO_T (RuleP rule1 X

		    RuleP rule2)

{

    AltP alt1;

    AltP alt2;

    if ((!types_equal_numbers (rule_param (rule1), rule_param (rule2))) ||

	(!types_equal_numbers (rule_result (rule1), rule_result (rule2))) ||

	(rule_has_empty_alt (rule1) != rule_has_empty_alt (rule2)) ||

	(!alt_equal (rule_get_handler (rule1), rule_get_handler (rule2))) ||

	(!non_local_list_is_empty (rule_non_locals (rule1))) ||

	(!non_local_list_is_empty (rule_non_locals (rule2)))) {

	return (FALSE);

    }

    for (alt1 = rule_alt_head (rule1), alt2 = rule_alt_head (rule2);

	 alt1 && alt2; alt1 = alt_next (alt1), alt2 = alt_next (alt2)) {

	ItemP item1;

	ItemP item2;

	for (item1 = alt_item_head (alt1), item2 = alt_item_head (alt2);

	     item1 && item2;

	     item1 = item_next (item1), item2 = item_next (item2)) {

	    if ((item_entry (item1) != item_entry (item2)) ||

		(!types_equal_numbers (item_param (item1),

				       item_param (item2))) ||

		(!types_equal_numbers (item_result (item1),

				       item_result (item2)))) {

		return (FALSE);

	    }

	}

	if (item1 || item2) {

	    return (FALSE);

	}

    }

    if (alt1 || alt2) {

	return (FALSE);

    }

    return (TRUE);

}

static BoolT

rule_do_replacements_1 PROTO_N ((alt, closure))

		       PROTO_T (AltP            alt X

				ReplaceClosureP closure)

{

    BoolT changed = FALSE;

    ItemP item;

    for (item = alt_item_head (alt); item; item = item_next (item)) {

	if (item_entry (item) == closure->from) {

	    item_set_entry (item, closure->to);

	    changed = TRUE;

	}

    }

    return (changed);

}

static void

rule_do_replacements PROTO_N ((entry, gclosure))

		     PROTO_T (EntryP   entry X

			      GenericP gclosure)

{

    ReplaceClosureP closure = (ReplaceClosureP) gclosure;

    if (entry_is_rule (entry)) {

	RuleP rule    = entry_get_rule (entry);

	BoolT changed = FALSE;

	AltP  alt;

	if ((alt = rule_get_handler (rule)) != NIL (AltP)) {

	    if (rule_do_replacements_1 (alt, closure)) {

		changed = TRUE;

	    }

	}

	for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

	    if (rule_do_replacements_1 (alt, closure)) {

		changed = TRUE;

	    }

	}

	if (changed) {

	    rule_reorder (rule);

	}

    }

}

static BoolT

rule_remove_duplicates_1 PROTO_N ((rule_ref, table))

			 PROTO_T (RuleP *rule_ref X

				  TableP table)

{

    BoolT did_remove = FALSE;

    RuleP rule;

    while ((rule = *rule_ref) != NIL (RuleP)) {

	RuleP *inner_rule_ref = rule_get_next_in_table_ref (rule);

	RuleP  inner_rule;

	while ((inner_rule = *inner_rule_ref) != NIL (RuleP)) {

	    if (rule_equal (rule, inner_rule)) {

		ReplaceClosureT closure;

		if (rule_is_required (inner_rule)) {

		    closure.from = rule_entry (rule);

		    closure.to   = rule_entry (inner_rule);

		    *rule_ref    = rule_get_next_in_table (rule);

		} else {

		    closure.from    = rule_entry (inner_rule);

		    closure.to      = rule_entry (rule);

		    *inner_rule_ref = rule_get_next_in_table (inner_rule);

		}

		table_iter (table, rule_do_replacements, (GenericP) &closure);

		did_remove = TRUE;

		if (rule != *rule_ref) {

		    goto removed_rule;

		}

	    } else {

		inner_rule_ref = rule_get_next_in_table_ref (inner_rule);

	    }

	}

	rule_ref = rule_get_next_in_table_ref (rule);

      removed_rule:;

    }

    return (did_remove);

}

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

void

rule_remove_duplicates PROTO_N ((table, predicate_id))

		       PROTO_T (TableP table X

				EntryP predicate_id)

{

    BoolT    did_remove;

    unsigned i;

    for (i = 0; i < EQUALITY_TABLE_SIZE; i ++) {

	equality_table [i] = NIL (RuleP);

    }

    table_iter (table, rule_hash_for_comparison, (GenericP) predicate_id);

    do {

	did_remove = FALSE;

	for (i = 0; i < EQUALITY_TABLE_SIZE; i ++) {

	    if (rule_remove_duplicates_1 (&(equality_table [i]), table)) {

		did_remove = TRUE;

	    }

	}

    } while (did_remove);

}

/*

 * Local variables(smf):

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

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

 * end:

**/