1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
|
/**************************************************************/
/* ********************************************************** */
/* * * */
/* * TERMINATOR * */
/* * * */
/* * $Module: REDRULES * */
/* * * */
/* * Copyright (C) 1999, 2000, 2001 MPI fuer Informatik * */
/* * * */
/* * This program is free software; you can redistribute * */
/* * it and/or modify it under the terms of the FreeBSD * */
/* * Licence. * */
/* * * */
/* * This program 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 LICENCE file * */
/* * for more details. * */
/* * * */
/* * * */
/* $Revision: 1.2 $ * */
/* $State: Exp $ * */
/* $Date: 2010-02-22 14:10:00 $ * */
/* $Author: weidenb $ * */
/* * * */
/* * Contact: * */
/* * Christoph Weidenbach * */
/* * MPI fuer Informatik * */
/* * Stuhlsatzenhausweg 85 * */
/* * 66123 Saarbruecken * */
/* * Email: spass@mpi-inf.mpg.de * */
/* * Germany * */
/* * * */
/* ********************************************************** */
/**************************************************************/
/* $RCSfile: terminator.c,v $ */
/**************************************************************/
/* Includes */
/**************************************************************/
#include "terminator.h"
#include "list.h"
static LIST red_GetTerminatorPartnerLits(TERM Atom, LITERAL Lit,
BOOL UnitsOnly, LIST IndexList)
/**************************************************************
INPUT: An atom, a literal, a boolean flag and a list of SHARED_INDEXes.
RETURNS: A list of literals with sign complementary to <Lit>
that are unifiable with <Atom>. The literals are searched
in all SHARED_INDEXes from <IndexList>. Additionally,
if <Unitsonly> is true, only literals from unit clauses
are returned.
EFFECT: <Atom> is a copy of <Lit> where some substitution
was applied and equality literals might have been swapped.
<Lit> is just needed to check whether the unifiable
literals are complementary.
***************************************************************/
{
LIST Result, Unifiers, LitScan;
LITERAL NextLit;
Result = list_Nil();
for ( ; !list_Empty(IndexList); IndexList = list_Cdr(IndexList)) {
Unifiers = st_GetUnifier(cont_LeftContext(),
sharing_Index(list_Car(IndexList)),
cont_RightContext(), Atom);
for ( ; !list_Empty(Unifiers); Unifiers = list_Pop(Unifiers)) {
if (!term_IsVariable(list_Car(Unifiers))) {
for (LitScan = sharing_NAtomDataList(list_Car(Unifiers));
!list_Empty(LitScan); LitScan = list_Cdr(LitScan)) {
NextLit = list_Car(LitScan);
if (clause_LiteralsAreComplementary(Lit, NextLit) &&
(!UnitsOnly || clause_Length(clause_LiteralOwningClause(NextLit))==1))
/* The partner literals must have complementary sign and
if <UnitsOnly> == TRUE they must be from unit clauses. */
Result = list_Cons(NextLit, Result);
}
}
}
}
return Result;
}
static CLAUSE red_CreateTerminatorEmptyClause(LIST FoundMap, FLAGSTORE Flags,
PRECEDENCE Precedence)
/**************************************************************
INPUT: A list of pairs (l1, l2), where l1 and l2 are unifiable
literals with complementary sign and a flag store.
More accurately, a substitution s exists,
such that l1 s = l2 s for all pairs (l1,l2) in
<FoundMap>.
For all literals l from the involved clauses
there exists one pair (l1,l2) in <FoundMap>
with l1=l or l2=l.
The flags store and the precedence are needed to create
the new clause.
RETURNS: A newly created empty clause, where the data
(parents,...) is set according to <FoundMap>.
***************************************************************/
{
CLAUSE Result, PClause;
LITERAL Lit;
LIST Parents;
NAT depth;
Result = clause_Create(list_Nil(), list_Nil(), list_Nil(), Flags, Precedence);
Parents = list_Nil();
depth = 0;
for (; !list_Empty(FoundMap); FoundMap = list_Cdr(FoundMap)) {
Lit = list_PairSecond(list_Car(FoundMap));
PClause = clause_LiteralOwningClause(Lit);
Parents = list_Cons(PClause, Parents);
depth = misc_Max(depth, clause_Depth(PClause));
clause_AddParentClause(Result, clause_Number(PClause));
clause_AddParentLiteral(Result, clause_LiteralGetIndex(Lit));
Lit = list_PairFirst(list_Car(FoundMap));
PClause = clause_LiteralOwningClause(Lit);
Parents = list_Cons(PClause, Parents);
depth = misc_Max(depth, clause_Depth(PClause));
clause_AddParentClause(Result, clause_Number(PClause));
clause_AddParentLiteral(Result, clause_LiteralGetIndex(Lit));
}
clause_SetFromTerminator(Result);
clause_SetDepth(Result, depth+1);
clause_SetSplitDataFromList(Result, Parents);
list_Delete(Parents);
return Result;
}
static BOOL red_TerminatorLitIsBetter(LITERAL L1, NAT S1, LITERAL L2, NAT S2)
/**************************************************************
INPUT: Two literals and its sizes wrt. some substitution.
RETURNS: TRUE, if <L1> is 'better' than <L2>, FALSE otherwise.
EFFECT: 1. Positive literals are 'better' than negative literals
2. If both literals have the same sign, the bigger literal
is better.
This is an heuristic that has shown to be useful in practice.
This function is used as parameter for the function
clause_MoveBestLiteralToFront.
***************************************************************/
{
if ((clause_LiteralIsNegative(L2) && clause_LiteralIsPositive(L1)) ||
/* The following conditions do the same as this condition: */
/* (!clause_LiteralsAreComplementary(L1, L2) && S1 > S2) */
(clause_LiteralIsPositive(L1) && S1 > S2) ||
(clause_LiteralIsNegative(L2) && S1 > S2))
return TRUE;
else
return FALSE;
}
static CLAUSE red_SearchTerminator(NAT n, LIST RestLits, LIST FoundMap,
SUBST Subst, SYMBOL GlobalMaxVar,
LIST IndexList, FLAGSTORE Flags,
PRECEDENCE Precedence)
/**************************************************************
INPUT: A natural number, a list of literals, a list of pairs,
a substitution, the maximum variable occurring in all
involved clauses, a list of SHARED_INDEXes, a flag store
and a precedence.
RETURNS: An empty clause, if a terminator situation was found,
NULL otherwise.
EFFECT: This recursive function implements the search for
a terminator situation with at most <n> non-unit clauses.
<RestLits> is the lists of literals actually missing
a complementary partner literal.
<FoundMap> is a list of pairs (l1,l2), where l1 and l2
are complementary, unifiable literals.
<Subst> is the common substitution of all those pairs.
<GlobalMaxVar> is the maximum variable from all
involved clauses.
To enable the search all involved clauses are made
variable-disjoint.
At the moment the function stops, if ANY terminator
situation occurred. This might not be desirable
if splitting is enabled, since there might be other
terminator situations resulting in an empty clause
of lower split level.
The flag store and the precedence are needed to create
the new clause.
***************************************************************/
{
if (list_Empty(RestLits)) {
/* We found a terminator situation, so stop the recursion */
return red_CreateTerminatorEmptyClause(FoundMap, Flags, Precedence);
} else {
CLAUSE Result, PClauseCopy;
LITERAL Lit, PLit;
SYMBOL NewMaxVar;
SUBST NewSubst, RightSubst;
TERM AtomCopy;
LIST ClashList, ToDoList;
BOOL Swapped;
NAT Limit;
int PLitInd;
Swapped = FALSE;
Result = clause_Null();
clause_MoveBestLiteralToFront(RestLits, Subst, GlobalMaxVar,
red_TerminatorLitIsBetter);
Lit = list_Car(RestLits);
RestLits = list_Cdr(RestLits);
AtomCopy = subst_Apply(Subst, term_Copy(clause_LiteralAtom(Lit)));
/* The following 'endless' loop runs twice for equality literals */
/* and only once for other literals. */
while (TRUE) {
ClashList = red_GetTerminatorPartnerLits(AtomCopy, Lit, n==0, IndexList);
for (; !list_Empty(ClashList) && Result==NULL;
ClashList = list_Pop(ClashList)) {
PLit = list_Car(ClashList);
PLitInd = clause_LiteralGetIndex(PLit);
PClauseCopy = clause_Copy(clause_LiteralOwningClause(PLit));
Limit = clause_Length(PClauseCopy) == 1 ? n : n-1;
clause_RenameVarsBiggerThan(PClauseCopy, GlobalMaxVar);
PLit = clause_GetLiteral(PClauseCopy, PLitInd);
FoundMap = list_Cons(list_PairCreate(Lit, PLit), FoundMap);
ToDoList = clause_GetLiteralListExcept(PClauseCopy, PLitInd);
ToDoList = list_Nconc(ToDoList, list_Copy(RestLits));
NewMaxVar = clause_SearchMaxVar(PClauseCopy);
if (symbol_GreaterVariable(GlobalMaxVar, NewMaxVar))
NewMaxVar = GlobalMaxVar;
cont_Check();
if (!unify_UnifyNoOC(cont_LeftContext(), AtomCopy,
cont_RightContext(), clause_LiteralAtom(PLit))) {
misc_StartErrorReport();
misc_ErrorReport("\n In red_SearchTerminator: Unification failed.");
misc_FinishErrorReport();
}
subst_ExtractUnifier(cont_LeftContext(), &NewSubst,
cont_RightContext(), &RightSubst);
cont_Reset();
/* The domains of both substitutions are disjoint */
/* so we do just a simple union operation. */
NewSubst = subst_NUnion(NewSubst, RightSubst);
RightSubst = NewSubst;
NewSubst = subst_Compose(NewSubst, subst_Copy(Subst));
subst_Delete(RightSubst);
Result = red_SearchTerminator(Limit, ToDoList, FoundMap, NewSubst,
NewMaxVar, IndexList, Flags, Precedence);
clause_Delete(PClauseCopy);
subst_Delete(NewSubst);
list_Delete(ToDoList);
list_PairFree(list_Car(FoundMap));
FoundMap = list_Pop(FoundMap);
}
/* loop control */
if (!fol_IsEquality(AtomCopy) || Swapped || Result!=NULL)
break;
else {
list_Delete(ClashList);
term_EqualitySwap(AtomCopy);
Swapped = TRUE;
}
}
/* cleanup */
term_Delete(AtomCopy);
/* <ClashList> may be non-empty since the loop stops */
/* if a terminator was found. */
list_Delete(ClashList);
return Result;
}
}
CLAUSE red_Terminator(CLAUSE RedClause, NAT n, SHARED_INDEX WoIndex,
SHARED_INDEX UsIndex, FLAGSTORE Flags,
PRECEDENCE Precedence)
/**************************************************************
INPUT: A clause, two shared indexes, a number <n>
restricting the number of non-unit clauses in
a possible terminator situation, a flag store
and a precedence.
RETURNS: An empty clause if a terminator with at most <n>
non-unit clauses is found, NULL otherwise.
EFFECT: See also description of red_SearchTerminator.
***************************************************************/
{
LIST Rest, IndexList;
CLAUSE Result;
if (clause_Length(RedClause) > 1) /* non-unit clause */
n--;
/* Pass the indexes as a list to sub-functions */
IndexList = list_Cons(WoIndex, list_List(UsIndex));
Rest = clause_GetLiteralList(RedClause);
Result = red_SearchTerminator(n, Rest, list_Nil(), subst_Nil(),
clause_MaxVar(RedClause), IndexList, Flags,
Precedence);
/* cleanup */
list_Delete(IndexList);
list_Delete(Rest);
return Result;
}
|
