summaryrefslogtreecommitdiffstats
path: root/src/bdd/cudd/cuddSubsetSP.c
blob: 36848eecd2592ae5514f9b263b72660f7c117b28 (plain)
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
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
/**CFile***********************************************************************

  FileName    [cuddSubsetSP.c]

  PackageName [cudd]

  Synopsis [Procedure to subset the given BDD choosing the shortest paths
            (largest cubes) in the BDD.]


  Description  [External procedures included in this module:
                <ul>
                <li> Cudd_SubsetShortPaths()
                <li> Cudd_SupersetShortPaths()
                </ul>
                Internal procedures included in this module:
                <ul>
                <li> cuddSubsetShortPaths()
                </ul>
                Static procedures included in this module:
                <ul>
                <li> BuildSubsetBdd()
                <li> CreatePathTable()
                <li> AssessPathLength()
                <li> CreateTopDist()
                <li> CreateBotDist()
                <li> ResizeNodeDistPages()
                <li> ResizeQueuePages()
                <li> stPathTableDdFree()
                </ul>
                ]

  SeeAlso     [cuddSubsetHB.c]

  Author      [Kavita Ravi]

  Copyright   [Copyright (c) 1995-2004, Regents of the University of Colorado

  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:

  Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

  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.

  Neither the name of the University of Colorado 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 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.]

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

#include "misc/util/util_hack.h"
#include "cuddInt.h"

ABC_NAMESPACE_IMPL_START



/*---------------------------------------------------------------------------*/
/* Constant declarations                                                     */
/*---------------------------------------------------------------------------*/

#define DEFAULT_PAGE_SIZE 2048 /* page size to store the BFS queue element type */
#define DEFAULT_NODE_DIST_PAGE_SIZE 2048 /*  page sizesto store NodeDist_t type */
#define MAXSHORTINT     ((DdHalfWord) ~0) /* constant defined to store
                                           * maximum distance of a node
                                           * from the root or the
                                           * constant
                                           */
#define INITIAL_PAGES 128 /* number of initial pages for the
                           * queue/NodeDist_t type */

/*---------------------------------------------------------------------------*/
/* Stucture declarations                                                     */
/*---------------------------------------------------------------------------*/

/* structure created to store subset results for each node and distances with
 * odd and even parity of the node from the root and sink. Main data structure
 * in this procedure.
 */
struct NodeDist{
    DdHalfWord oddTopDist;
    DdHalfWord evenTopDist;
    DdHalfWord oddBotDist;
    DdHalfWord evenBotDist;
    DdNode *regResult;
    DdNode *compResult;
};

/* assorted information needed by the BuildSubsetBdd procedure. */
struct AssortedInfo {
    unsigned int maxpath;
    int findShortestPath;
    int thresholdReached;
    st_table *maxpathTable;
    int threshold;
};

/*---------------------------------------------------------------------------*/
/* Type declarations                                                         */
/*---------------------------------------------------------------------------*/

typedef struct NodeDist NodeDist_t;

/*---------------------------------------------------------------------------*/
/* Variable declarations                                                     */
/*---------------------------------------------------------------------------*/

#ifndef lint
static char rcsid[] DD_UNUSED = "$Id: cuddSubsetSP.c,v 1.34 2009/02/19 16:23:19 fabio Exp $";
#endif

#ifdef DD_DEBUG
static int numCalls;
static int hits;
static int thishit;
#endif


static  int             memOut; /* flag to indicate out of memory */
static  DdNode          *zero, *one; /* constant functions */

static  NodeDist_t      **nodeDistPages; /* pointers to the pages */
static  int             nodeDistPageIndex; /* index to next element */
static  int             nodeDistPage; /* index to current page */
static  int             nodeDistPageSize = DEFAULT_NODE_DIST_PAGE_SIZE; /* page size */
static  int             maxNodeDistPages; /* number of page pointers */
static  NodeDist_t      *currentNodeDistPage; /* current page */

static  DdNode          ***queuePages; /* pointers to the pages */
static  int             queuePageIndex; /* index to next element */
static  int             queuePage; /* index to current page */
static  int             queuePageSize = DEFAULT_PAGE_SIZE; /* page size */
static  int             maxQueuePages; /* number of page pointers */
static  DdNode          **currentQueuePage; /* current page */


/*---------------------------------------------------------------------------*/
/* Macro declarations                                                        */
/*---------------------------------------------------------------------------*/

#ifdef __cplusplus
extern "C" {
#endif

/**AutomaticStart*************************************************************/

/*---------------------------------------------------------------------------*/
/* Static function prototypes                                                */
/*---------------------------------------------------------------------------*/

static void ResizeNodeDistPages (void);
static void ResizeQueuePages (void);
static void CreateTopDist (st_table *pathTable, int parentPage, int parentQueueIndex, int topLen, DdNode **childPage, int childQueueIndex, int numParents, FILE *fp);
static int CreateBotDist (DdNode *node, st_table *pathTable, unsigned int *pathLengthArray, FILE *fp);
static st_table * CreatePathTable (DdNode *node, unsigned int *pathLengthArray, FILE *fp);
static unsigned int AssessPathLength (unsigned int *pathLengthArray, int threshold, int numVars, unsigned int *excess, FILE *fp);
static DdNode * BuildSubsetBdd (DdManager *dd, st_table *pathTable, DdNode *node, struct AssortedInfo *info, st_table *subsetNodeTable);
static enum st_retval stPathTableDdFree (char *key, char *value, char *arg);

/**AutomaticEnd***************************************************************/

#ifdef __cplusplus
}
#endif

/*---------------------------------------------------------------------------*/
/* Definition of Exported functions                                          */
/*---------------------------------------------------------------------------*/


/**Function********************************************************************

  Synopsis    [Extracts a dense subset from a BDD with the shortest paths
  heuristic.]

  Description [Extracts a dense subset from a BDD.  This procedure
  tries to preserve the shortest paths of the input BDD, because they
  give many minterms and contribute few nodes.  This procedure may
  increase the number of nodes in trying to create the subset or
  reduce the number of nodes due to recombination as compared to the
  original BDD. Hence the threshold may not be strictly adhered to. In
  practice, recombination overshadows the increase in the number of
  nodes and results in small BDDs as compared to the threshold. The
  hardlimit specifies whether threshold needs to be strictly adhered
  to. If it is set to 1, the procedure ensures that result is never
  larger than the specified limit but may be considerably less than
  the threshold.  Returns a pointer to the BDD for the subset if
  successful; NULL otherwise.  The value for numVars should be as
  close as possible to the size of the support of f for better
  efficiency. However, it is safe to pass the value returned by
  Cudd_ReadSize for numVars. If 0 is passed, then the value returned
  by Cudd_ReadSize is used.]

  SideEffects [None]

  SeeAlso     [Cudd_SupersetShortPaths Cudd_SubsetHeavyBranch Cudd_ReadSize]

******************************************************************************/
DdNode *
Cudd_SubsetShortPaths(
  DdManager * dd /* manager */,
  DdNode * f /* function to be subset */,
  int  numVars /* number of variables in the support of f */,
  int  threshold /* maximum number of nodes in the subset */,
  int  hardlimit /* flag: 1 if threshold is a hard limit */)
{
    DdNode *subset;

    memOut = 0;
    do {
        dd->reordered = 0;
        subset = cuddSubsetShortPaths(dd, f, numVars, threshold, hardlimit);
    } while((dd->reordered ==1) && (!memOut));

    return(subset);

} /* end of Cudd_SubsetShortPaths */


/**Function********************************************************************

  Synopsis    [Extracts a dense superset from a BDD with the shortest paths
  heuristic.]

  Description [Extracts a dense superset from a BDD.  The procedure is
  identical to the subset procedure except for the fact that it
  receives the complement of the given function. Extracting the subset
  of the complement function is equivalent to extracting the superset
  of the function.  This procedure tries to preserve the shortest
  paths of the complement BDD, because they give many minterms and
  contribute few nodes.  This procedure may increase the number of
  nodes in trying to create the superset or reduce the number of nodes
  due to recombination as compared to the original BDD. Hence the
  threshold may not be strictly adhered to. In practice, recombination
  overshadows the increase in the number of nodes and results in small
  BDDs as compared to the threshold.  The hardlimit specifies whether
  threshold needs to be strictly adhered to. If it is set to 1, the
  procedure ensures that result is never larger than the specified
  limit but may be considerably less than the threshold. Returns a
  pointer to the BDD for the superset if successful; NULL
  otherwise. The value for numVars should be as close as possible to
  the size of the support of f for better efficiency.  However, it is
  safe to pass the value returned by Cudd_ReadSize for numVar.  If 0
  is passed, then the value returned by Cudd_ReadSize is used.]

  SideEffects [None]

  SeeAlso     [Cudd_SubsetShortPaths Cudd_SupersetHeavyBranch Cudd_ReadSize]

******************************************************************************/
DdNode *
Cudd_SupersetShortPaths(
  DdManager * dd /* manager */,
  DdNode * f /* function to be superset */,
  int  numVars /* number of variables in the support of f */,
  int  threshold /* maximum number of nodes in the subset */,
  int  hardlimit /* flag: 1 if threshold is a hard limit */)
{
    DdNode *subset, *g;

    g = Cudd_Not(f);
    memOut = 0;
    do {
        dd->reordered = 0;
        subset = cuddSubsetShortPaths(dd, g, numVars, threshold, hardlimit);
    } while((dd->reordered ==1) && (!memOut));

    return(Cudd_NotCond(subset, (subset != NULL)));

} /* end of Cudd_SupersetShortPaths */


/*---------------------------------------------------------------------------*/
/* Definition of internal functions                                          */
/*---------------------------------------------------------------------------*/


/**Function********************************************************************

  Synopsis    [The outermost procedure to return a subset of the given BDD
  with the shortest path lengths.]

  Description [The outermost procedure to return a subset of the given
  BDD with the largest cubes. The path lengths are calculated, the maximum
  allowable path length is determined and the number of nodes of this
  path length that can be used to build a subset. If the threshold is
  larger than the size of the original BDD, the original BDD is
  returned. ]

  SideEffects [None]

  SeeAlso     [Cudd_SubsetShortPaths]

******************************************************************************/
DdNode *
cuddSubsetShortPaths(
  DdManager * dd /* DD manager */,
  DdNode * f /* function to be subset */,
  int  numVars /* total number of variables in consideration */,
  int  threshold /* maximum number of nodes allowed in the subset */,
  int  hardlimit /* flag determining whether thershold should be respected strictly */)
{
    st_table *pathTable;
    DdNode *N, *subset;

    unsigned int  *pathLengthArray;
    unsigned int maxpath, oddLen, evenLen, pathLength, *excess;
    int i;
    NodeDist_t  *nodeStat;
    struct AssortedInfo *info;
    st_table *subsetNodeTable;

    one = DD_ONE(dd);
    zero = Cudd_Not(one);

    if (numVars == 0) {
      /* set default value */
      numVars = Cudd_ReadSize(dd);
    }

    if (threshold > numVars) {
        threshold = threshold - numVars;
    }
    if (f == NULL) {
        fprintf(dd->err, "Cannot partition, nil object\n");
        dd->errorCode = CUDD_INVALID_ARG;
        return(NULL);
    }
    if (Cudd_IsConstant(f))
        return (f);

    pathLengthArray = ABC_ALLOC(unsigned int, numVars+1);
    for (i = 0; i < numVars+1; i++) pathLengthArray[i] = 0;


#ifdef DD_DEBUG
    numCalls = 0;
#endif

    pathTable = CreatePathTable(f, pathLengthArray, dd->err);

    if ((pathTable == NULL) || (memOut)) {
        if (pathTable != NULL)
            st_free_table(pathTable);
        ABC_FREE(pathLengthArray);
        return (NIL(DdNode));
    }

    excess = ABC_ALLOC(unsigned int, 1);
    *excess = 0;
    maxpath = AssessPathLength(pathLengthArray, threshold, numVars, excess,
                               dd->err);

    if (maxpath != (unsigned) (numVars + 1)) {

        info = ABC_ALLOC(struct AssortedInfo, 1);
        info->maxpath = maxpath;
        info->findShortestPath = 0;
        info->thresholdReached = *excess;
        info->maxpathTable = st_init_table(st_ptrcmp, st_ptrhash);
        info->threshold = threshold;

#ifdef DD_DEBUG
        (void) fprintf(dd->out, "Path length array\n");
        for (i = 0; i < (numVars+1); i++) {
            if (pathLengthArray[i])
                (void) fprintf(dd->out, "%d ",i);
        }
        (void) fprintf(dd->out, "\n");
        for (i = 0; i < (numVars+1); i++) {
            if (pathLengthArray[i])
                (void) fprintf(dd->out, "%d ",pathLengthArray[i]);
        }
        (void) fprintf(dd->out, "\n");
        (void) fprintf(dd->out, "Maxpath  = %d, Thresholdreached = %d\n",
                       maxpath, info->thresholdReached);
#endif

        N = Cudd_Regular(f);
        if (!st_lookup(pathTable, (const char *)N, (char **)&nodeStat)) {
            fprintf(dd->err, "Something wrong, root node must be in table\n");
            dd->errorCode = CUDD_INTERNAL_ERROR;
            ABC_FREE(excess);
            ABC_FREE(info);
            return(NULL);
        } else {
            if ((nodeStat->oddTopDist != MAXSHORTINT) &&
                (nodeStat->oddBotDist != MAXSHORTINT))
                oddLen = (nodeStat->oddTopDist + nodeStat->oddBotDist);
            else
                oddLen = MAXSHORTINT;

            if ((nodeStat->evenTopDist != MAXSHORTINT) &&
                (nodeStat->evenBotDist != MAXSHORTINT))
                evenLen = (nodeStat->evenTopDist +nodeStat->evenBotDist);
            else
                evenLen = MAXSHORTINT;

            pathLength = (oddLen <= evenLen) ? oddLen : evenLen;
            if (pathLength > maxpath) {
                (void) fprintf(dd->err, "All computations are bogus, since root has path length greater than max path length within threshold %u, %u\n", maxpath, pathLength);
                dd->errorCode = CUDD_INTERNAL_ERROR;
                return(NULL);
            }
        }

#ifdef DD_DEBUG
        numCalls = 0;
        hits = 0;
        thishit = 0;
#endif
        /* initialize a table to store computed nodes */
        if (hardlimit) {
            subsetNodeTable = st_init_table(st_ptrcmp, st_ptrhash);
        } else {
            subsetNodeTable = NIL(st_table);
        }
        subset = BuildSubsetBdd(dd, pathTable, f, info, subsetNodeTable);
        if (subset != NULL) {
            cuddRef(subset);
        }
        /* record the number of times a computed result for a node is hit */

#ifdef DD_DEBUG
        (void) fprintf(dd->out, "Hits = %d, New==Node = %d, NumCalls = %d\n",
                hits, thishit, numCalls);
#endif

        if (subsetNodeTable != NIL(st_table)) {
            st_free_table(subsetNodeTable);
        }
        st_free_table(info->maxpathTable);
        st_foreach(pathTable, stPathTableDdFree, (char *)dd);

        ABC_FREE(info);

    } else {/* if threshold larger than size of dd */
        subset = f;
        cuddRef(subset);
    }
    ABC_FREE(excess);
    st_free_table(pathTable);
    ABC_FREE(pathLengthArray);
    for (i = 0; i <= nodeDistPage; i++) ABC_FREE(nodeDistPages[i]);
    ABC_FREE(nodeDistPages);

#ifdef DD_DEBUG
    /* check containment of subset in f */
    if (subset != NULL) {
        DdNode *check;
        check = Cudd_bddIteConstant(dd, subset, f, one);
        if (check != one) {
            (void) fprintf(dd->err, "Wrong partition\n");
            dd->errorCode = CUDD_INTERNAL_ERROR;
            return(NULL);
        }
    }
#endif

    if (subset != NULL) {
        cuddDeref(subset);
        return(subset);
    } else {
        return(NULL);
    }

} /* end of cuddSubsetShortPaths */


/*---------------------------------------------------------------------------*/
/* Definition of static functions                                            */
/*---------------------------------------------------------------------------*/


/**Function********************************************************************

  Synopsis    [Resize the number of pages allocated to store the distances
  related to each node.]

  Description [Resize the number of pages allocated to store the distances
  related to each node. The procedure  moves the counter to the
  next page when the end of the page is reached and allocates new
  pages when necessary. ]

  SideEffects [Changes the size of  pages, page, page index, maximum
  number of pages freeing stuff in case of memory out. ]

  SeeAlso     []

******************************************************************************/
static void
ResizeNodeDistPages(void)
{
    int i;
    NodeDist_t **newNodeDistPages;

    /* move to next page */
    nodeDistPage++;

    /* If the current page index is larger than the number of pages
     * allocated, allocate a new page array. Page numbers are incremented by
     * INITIAL_PAGES
     */
    if (nodeDistPage == maxNodeDistPages) {
        newNodeDistPages = ABC_ALLOC(NodeDist_t *,maxNodeDistPages + INITIAL_PAGES);
        if (newNodeDistPages == NULL) {
            for (i = 0; i < nodeDistPage; i++) ABC_FREE(nodeDistPages[i]);
            ABC_FREE(nodeDistPages);
            memOut = 1;
            return;
        } else {
            for (i = 0; i < maxNodeDistPages; i++) {
                newNodeDistPages[i] = nodeDistPages[i];
            }
            /* Increase total page count */
            maxNodeDistPages += INITIAL_PAGES;
            ABC_FREE(nodeDistPages);
            nodeDistPages = newNodeDistPages;
        }
    }
    /* Allocate a new page */
    currentNodeDistPage = nodeDistPages[nodeDistPage] = ABC_ALLOC(NodeDist_t,
                                                              nodeDistPageSize);
    if (currentNodeDistPage == NULL) {
        for (i = 0; i < nodeDistPage; i++) ABC_FREE(nodeDistPages[i]);
        ABC_FREE(nodeDistPages);
        memOut = 1;
        return;
    }
    /* reset page index */
    nodeDistPageIndex = 0;
    return;

} /* end of ResizeNodeDistPages */


/**Function********************************************************************

  Synopsis    [Resize the number of pages allocated to store nodes in the BFS
  traversal of the Bdd  .]

  Description [Resize the number of pages allocated to store nodes in the BFS
  traversal of the Bdd. The procedure  moves the counter to the
  next page when the end of the page is reached and allocates new
  pages when necessary.]

  SideEffects [Changes the size of pages, page, page index, maximum
  number of pages freeing stuff in case of memory out. ]

  SeeAlso     []

******************************************************************************/
static void
ResizeQueuePages(void)
{
    int i;
    DdNode ***newQueuePages;

    queuePage++;
    /* If the current page index is larger than the number of pages
     * allocated, allocate a new page array. Page numbers are incremented by
     * INITIAL_PAGES
     */
    if (queuePage == maxQueuePages) {
        newQueuePages = ABC_ALLOC(DdNode **,maxQueuePages + INITIAL_PAGES);
        if (newQueuePages == NULL) {
            for (i = 0; i < queuePage; i++) ABC_FREE(queuePages[i]);
            ABC_FREE(queuePages);
            memOut = 1;
            return;
        } else {
            for (i = 0; i < maxQueuePages; i++) {
                newQueuePages[i] = queuePages[i];
            }
            /* Increase total page count */
            maxQueuePages += INITIAL_PAGES;
            ABC_FREE(queuePages);
            queuePages = newQueuePages;
        }
    }
    /* Allocate a new page */
    currentQueuePage = queuePages[queuePage] = ABC_ALLOC(DdNode *,queuePageSize);
    if (currentQueuePage == NULL) {
        for (i = 0; i < queuePage; i++) ABC_FREE(queuePages[i]);
        ABC_FREE(queuePages);
        memOut = 1;
        return;
    }
    /* reset page index */
    queuePageIndex = 0;
    return;

} /* end of ResizeQueuePages */


/**Function********************************************************************

  Synopsis    [ Labels each node with its shortest distance from the root]

  Description [ Labels each node with its shortest distance from the root.
  This is done in a BFS search of the BDD. The nodes are processed
  in a queue implemented as pages(array) to reduce memory fragmentation.
  An entry is created for each node visited. The distance from the root
  to the node with the corresponding  parity is updated. The procedure
  is called recursively each recusion level handling nodes at a given
  level from the root.]


  SideEffects [Creates entries in the pathTable]

  SeeAlso     [CreatePathTable CreateBotDist]

******************************************************************************/
static void
CreateTopDist(
  st_table * pathTable /* hast table to store path lengths */,
  int  parentPage /* the pointer to the page on which the first parent in the queue is to be found. */,
  int  parentQueueIndex /* pointer to the first parent on the page */,
  int  topLen /* current distance from the root */,
  DdNode ** childPage /* pointer to the page on which the first child is to be added. */,
  int  childQueueIndex /* pointer to the first child */,
  int  numParents /* number of parents to process in this recursive call */,
  FILE *fp /* where to write messages */)
{
    NodeDist_t *nodeStat;
    DdNode *N, *Nv, *Nnv, *node, *child, *regChild;
    int  i;
    int processingDone, childrenCount;

#ifdef DD_DEBUG
    numCalls++;

    /* assume this procedure comes in with only the root node*/
    /* set queue index to the next available entry for addition */
    /* set queue page to page of addition */
    if ((queuePages[parentPage] == childPage) && (parentQueueIndex ==
                                                  childQueueIndex)) {
        fprintf(fp, "Should not happen that they are equal\n");
    }
    assert(queuePageIndex == childQueueIndex);
    assert(currentQueuePage == childPage);
#endif
    /* number children added to queue is initialized , needed for
     * numParents in the next call
     */
    childrenCount = 0;
    /* process all the nodes in this level */
    while (numParents) {
        numParents--;
        if (parentQueueIndex == queuePageSize) {
            parentPage++;
            parentQueueIndex = 0;
        }
        /* a parent to process */
        node = *(queuePages[parentPage] + parentQueueIndex);
        parentQueueIndex++;
        /* get its children */
        N = Cudd_Regular(node);
        Nv = Cudd_T(N);
        Nnv = Cudd_E(N);

        Nv = Cudd_NotCond(Nv, Cudd_IsComplement(node));
        Nnv = Cudd_NotCond(Nnv, Cudd_IsComplement(node));

        processingDone = 2;
        while (processingDone) {
            /* processing the THEN and the ELSE children, the THEN
             * child first
             */
            if (processingDone == 2) {
                child = Nv;
            } else {
                child = Nnv;
            }

            regChild = Cudd_Regular(child);
            /* dont process if the child is a constant */
            if (!Cudd_IsConstant(child)) {
                /* check is already visited, if not add a new entry in
                 * the path Table
                 */
                if (!st_lookup(pathTable, (const char *)regChild, (char **)&nodeStat)) {
                    /* if not in table, has never been visited */
                    /* create entry for table */
                    if (nodeDistPageIndex == nodeDistPageSize)
                        ResizeNodeDistPages();
                    if (memOut) {
                        for (i = 0; i <= queuePage; i++) ABC_FREE(queuePages[i]);
                        ABC_FREE(queuePages);
                        st_free_table(pathTable);
                        return;
                    }
                    /* New entry for child in path Table is created here */
                    nodeStat = currentNodeDistPage + nodeDistPageIndex;
                    nodeDistPageIndex++;

                    /* Initialize fields of the node data */
                    nodeStat->oddTopDist = MAXSHORTINT;
                    nodeStat->evenTopDist = MAXSHORTINT;
                    nodeStat->evenBotDist = MAXSHORTINT;
                    nodeStat->oddBotDist = MAXSHORTINT;
                    nodeStat->regResult = NULL;
                    nodeStat->compResult = NULL;
                    /* update the table entry element, the distance keeps
                     * track of the parity of the path from the root
                     */
                    if (Cudd_IsComplement(child)) {
                        nodeStat->oddTopDist = (DdHalfWord) topLen + 1;
                    } else {
                        nodeStat->evenTopDist = (DdHalfWord) topLen + 1;
                    }

                    /* insert entry element for  child in the table */
                    if (st_insert(pathTable, (char *)regChild,
                                  (char *)nodeStat) == ST_OUT_OF_MEM) {
                        memOut = 1;
                        for (i = 0; i <= nodeDistPage; i++)
                            ABC_FREE(nodeDistPages[i]);
                        ABC_FREE(nodeDistPages);
                        for (i = 0; i <= queuePage; i++) ABC_FREE(queuePages[i]);
                        ABC_FREE(queuePages);
                        st_free_table(pathTable);
                        return;
                    }

                    /* Create list element for this child to process its children.
                     * If this node has been processed already, then it appears
                     * in the path table and hence is never added to the list
                     * again.
                     */

                    if (queuePageIndex == queuePageSize) ResizeQueuePages();
                    if (memOut) {
                        for (i = 0; i <= nodeDistPage; i++)
                            ABC_FREE(nodeDistPages[i]);
                        ABC_FREE(nodeDistPages);
                        st_free_table(pathTable);
                        return;
                    }
                    *(currentQueuePage + queuePageIndex) = child;
                    queuePageIndex++;

                    childrenCount++;
                } else {
                    /* if not been met in a path with this parity before */
                    /* put in list */
                    if (((Cudd_IsComplement(child)) && (nodeStat->oddTopDist ==
                          MAXSHORTINT)) || ((!Cudd_IsComplement(child)) &&
                                  (nodeStat->evenTopDist == MAXSHORTINT))) {

                        if (queuePageIndex == queuePageSize) ResizeQueuePages();
                        if (memOut) {
                            for (i = 0; i <= nodeDistPage; i++)
                                ABC_FREE(nodeDistPages[i]);
                            ABC_FREE(nodeDistPages);
                            st_free_table(pathTable);
                            return;

                        }
                        *(currentQueuePage + queuePageIndex) = child;
                        queuePageIndex++;

                        /* update the distance with the appropriate parity */
                        if (Cudd_IsComplement(child)) {
                            nodeStat->oddTopDist = (DdHalfWord) topLen + 1;
                        } else {
                            nodeStat->evenTopDist = (DdHalfWord) topLen + 1;
                        }
                        childrenCount++;
                    }

                } /* end of else (not found in st_table) */
            } /*end of if Not constant child */
            processingDone--;
        } /*end of while processing Nv, Nnv */
    }  /*end of while numParents */

#ifdef DD_DEBUG
    assert(queuePages[parentPage] == childPage);
    assert(parentQueueIndex == childQueueIndex);
#endif

    if (childrenCount != 0) {
        topLen++;
        childPage = currentQueuePage;
        childQueueIndex = queuePageIndex;
        CreateTopDist(pathTable, parentPage, parentQueueIndex, topLen,
                      childPage, childQueueIndex, childrenCount, fp);
    }

    return;

} /* end of CreateTopDist */


/**Function********************************************************************

  Synopsis    [ Labels each node with the shortest distance from the constant.]

  Description [Labels each node with the shortest distance from the constant.
  This is done in a DFS search of the BDD. Each node has an odd
  and even parity distance from the sink (since there exists paths to both
  zero and one) which is less than MAXSHORTINT. At each node these distances
  are updated using the minimum distance of its children from the constant.
  SInce now both the length from the root and child is known, the minimum path
  length(length of the shortest path between the root and the constant that
  this node lies on) of this node can be calculated and used to update the
  pathLengthArray]

  SideEffects [Updates Path Table and path length array]

  SeeAlso     [CreatePathTable CreateTopDist AssessPathLength]

******************************************************************************/
static int
CreateBotDist(
  DdNode * node /* current node */,
  st_table * pathTable /* path table with path lengths */,
  unsigned int * pathLengthArray /* array that stores number of nodes belonging to a particular path length. */,
  FILE *fp /* where to write messages */)
{
    DdNode *N, *Nv, *Nnv;
    DdNode *realChild;
    DdNode *child, *regChild;
    NodeDist_t *nodeStat, *nodeStatChild;
    unsigned int  oddLen, evenLen, pathLength;
    DdHalfWord botDist;
    int processingDone;

    if (Cudd_IsConstant(node))
        return(1);
    N = Cudd_Regular(node);
    /* each node has one table entry */
    /* update as you go down the min dist of each node from
       the root in each (odd and even) parity */
    if (!st_lookup(pathTable, (const char *)N, (char **)&nodeStat)) {
        fprintf(fp, "Something wrong, the entry doesn't exist\n");
        return(0);
    }

    /* compute length of odd parity distances */
    if ((nodeStat->oddTopDist != MAXSHORTINT) &&
        (nodeStat->oddBotDist != MAXSHORTINT))
        oddLen = (nodeStat->oddTopDist + nodeStat->oddBotDist);
    else
        oddLen = MAXSHORTINT;

    /* compute length of even parity distances */
    if (!((nodeStat->evenTopDist == MAXSHORTINT) ||
          (nodeStat->evenBotDist == MAXSHORTINT)))
        evenLen = (nodeStat->evenTopDist +nodeStat->evenBotDist);
    else
        evenLen = MAXSHORTINT;

    /* assign pathlength to minimum of the two */
    pathLength = (oddLen <= evenLen) ? oddLen : evenLen;

    Nv = Cudd_T(N);
    Nnv = Cudd_E(N);

    /* process each child */
    processingDone = 0;
    while (processingDone != 2) {
        if (!processingDone) {
            child = Nv;
        } else {
            child = Nnv;
        }

        realChild = Cudd_NotCond(child, Cudd_IsComplement(node));
        regChild = Cudd_Regular(child);
        if (Cudd_IsConstant(realChild)) {
            /* Found a minterm; count parity and shortest distance
            ** from the constant.
            */
            if (Cudd_IsComplement(child))
                nodeStat->oddBotDist = 1;
            else
                nodeStat->evenBotDist = 1;
        } else {
            /* If node not in table, recur. */
            if (!st_lookup(pathTable, (const char *)regChild, (char **)&nodeStatChild)) {
                fprintf(fp, "Something wrong, node in table should have been created in top dist proc.\n");
                return(0);
            }

            if (nodeStatChild->oddBotDist == MAXSHORTINT) {
                if (nodeStatChild->evenBotDist == MAXSHORTINT) {
                    if (!CreateBotDist(realChild, pathTable, pathLengthArray, fp))
                        return(0);
                } else {
                    fprintf(fp, "Something wrong, both bot nodeStats should be there\n");
                    return(0);
                }
            }

            /* Update shortest distance from the constant depending on
            **  parity. */

            if (Cudd_IsComplement(child)) {
                /* If parity on the edge then add 1 to even distance
                ** of child to get odd parity distance and add 1 to
                ** odd distance of child to get even parity
                ** distance. Change distance of current node only if
                ** the calculated distance is less than existing
                ** distance. */
                if (nodeStatChild->oddBotDist != MAXSHORTINT)
                    botDist = nodeStatChild->oddBotDist + 1;
                else
                    botDist = MAXSHORTINT;
                if (nodeStat->evenBotDist > botDist )
                    nodeStat->evenBotDist = botDist;

                if (nodeStatChild->evenBotDist != MAXSHORTINT)
                    botDist = nodeStatChild->evenBotDist + 1;
                else
                    botDist = MAXSHORTINT;
                if (nodeStat->oddBotDist > botDist)
                    nodeStat->oddBotDist = botDist;

            } else {
                /* If parity on the edge then add 1 to even distance
                ** of child to get even parity distance and add 1 to
                ** odd distance of child to get odd parity distance.
                ** Change distance of current node only if the
                ** calculated distance is lesser than existing
                ** distance. */
                if (nodeStatChild->evenBotDist != MAXSHORTINT)
                    botDist = nodeStatChild->evenBotDist + 1;
                else
                    botDist = MAXSHORTINT;
                if (nodeStat->evenBotDist > botDist)
                    nodeStat->evenBotDist = botDist;

                if (nodeStatChild->oddBotDist != MAXSHORTINT)
                    botDist = nodeStatChild->oddBotDist + 1;
                else
                    botDist = MAXSHORTINT;
                if (nodeStat->oddBotDist > botDist)
                    nodeStat->oddBotDist = botDist;
            }
        } /* end of else (if not constant child ) */
        processingDone++;
    } /* end of while processing Nv, Nnv */

    /* Compute shortest path length on the fly. */
    if ((nodeStat->oddTopDist != MAXSHORTINT) &&
        (nodeStat->oddBotDist != MAXSHORTINT))
        oddLen = (nodeStat->oddTopDist + nodeStat->oddBotDist);
    else
        oddLen = MAXSHORTINT;

    if ((nodeStat->evenTopDist != MAXSHORTINT) &&
        (nodeStat->evenBotDist != MAXSHORTINT))
        evenLen = (nodeStat->evenTopDist +nodeStat->evenBotDist);
    else
        evenLen = MAXSHORTINT;

    /* Update path length array that has number of nodes of a particular
    ** path length. */
    if (oddLen < pathLength ) {
        if (pathLength != MAXSHORTINT)
            pathLengthArray[pathLength]--;
        if (oddLen != MAXSHORTINT)
            pathLengthArray[oddLen]++;
        pathLength = oddLen;
    }
    if (evenLen < pathLength ) {
        if (pathLength != MAXSHORTINT)
            pathLengthArray[pathLength]--;
        if (evenLen != MAXSHORTINT)
            pathLengthArray[evenLen]++;
    }

    return(1);

} /*end of CreateBotDist */


/**Function********************************************************************

  Synopsis    [ The outer procedure to label each node with its shortest
  distance from the root and constant]

  Description [ The outer procedure to label each node with its shortest
  distance from the root and constant. Calls CreateTopDist and CreateBotDist.
  The basis for computing the distance between root and constant is that
  the distance may be the sum of even distances from the node to the root
  and constant or the sum of odd distances from the node to the root and
  constant.  Both CreateTopDist and CreateBotDist create the odd and
  even parity distances from the root and constant respectively.]

  SideEffects [None]

  SeeAlso     [CreateTopDist CreateBotDist]

******************************************************************************/
static st_table *
CreatePathTable(
  DdNode * node /* root of function */,
  unsigned int * pathLengthArray /* array of path lengths to store nodes labeled with the various path lengths */,
  FILE *fp /* where to write messages */)
{

    st_table *pathTable;
    NodeDist_t *nodeStat;
    DdHalfWord topLen;
    DdNode *N;
    int i, numParents;
    int insertValue;
    DdNode **childPage;
    int parentPage;
    int childQueueIndex, parentQueueIndex;

    /* Creating path Table for storing data about nodes */
    pathTable = st_init_table(st_ptrcmp,st_ptrhash);

    /* initializing pages for info about each node */
    maxNodeDistPages = INITIAL_PAGES;
    nodeDistPages = ABC_ALLOC(NodeDist_t *, maxNodeDistPages);
    if (nodeDistPages == NULL) {
        goto OUT_OF_MEM;
    }
    nodeDistPage = 0;
    currentNodeDistPage = nodeDistPages[nodeDistPage] =
        ABC_ALLOC(NodeDist_t, nodeDistPageSize);
    if (currentNodeDistPage == NULL) {
        for (i = 0; i <= nodeDistPage; i++) ABC_FREE(nodeDistPages[i]);
        ABC_FREE(nodeDistPages);
        goto OUT_OF_MEM;
    }
    nodeDistPageIndex = 0;

    /* Initializing pages for the BFS search queue, implemented as an array. */
    maxQueuePages = INITIAL_PAGES;
    queuePages = ABC_ALLOC(DdNode **, maxQueuePages);
    if (queuePages == NULL) {
        goto OUT_OF_MEM;
    }
    queuePage = 0;
    currentQueuePage  = queuePages[queuePage] = ABC_ALLOC(DdNode *, queuePageSize);
    if (currentQueuePage == NULL) {
        for (i = 0; i <= queuePage; i++) ABC_FREE(queuePages[i]);
        ABC_FREE(queuePages);
        goto OUT_OF_MEM;
    }
    queuePageIndex = 0;

    /* Enter the root node into the queue to start with. */
    parentPage = queuePage;
    parentQueueIndex = queuePageIndex;
    topLen = 0;
    *(currentQueuePage + queuePageIndex) = node;
    queuePageIndex++;
    childPage = currentQueuePage;
    childQueueIndex = queuePageIndex;

    N = Cudd_Regular(node);

    if (nodeDistPageIndex == nodeDistPageSize) ResizeNodeDistPages();
    if (memOut) {
        for (i = 0; i <= nodeDistPage; i++) ABC_FREE(nodeDistPages[i]);
        ABC_FREE(nodeDistPages);
        for (i = 0; i <= queuePage; i++) ABC_FREE(queuePages[i]);
        ABC_FREE(queuePages);
        st_free_table(pathTable);
        goto OUT_OF_MEM;
    }

    nodeStat = currentNodeDistPage + nodeDistPageIndex;
    nodeDistPageIndex++;

    nodeStat->oddTopDist = MAXSHORTINT;
    nodeStat->evenTopDist = MAXSHORTINT;
    nodeStat->evenBotDist = MAXSHORTINT;
    nodeStat->oddBotDist = MAXSHORTINT;
    nodeStat->regResult = NULL;
    nodeStat->compResult = NULL;

    insertValue = st_insert(pathTable, (char *)N, (char *)nodeStat);
    if (insertValue == ST_OUT_OF_MEM) {
        memOut = 1;
        for (i = 0; i <= nodeDistPage; i++) ABC_FREE(nodeDistPages[i]);
        ABC_FREE(nodeDistPages);
        for (i = 0; i <= queuePage; i++) ABC_FREE(queuePages[i]);
        ABC_FREE(queuePages);
        st_free_table(pathTable);
        goto OUT_OF_MEM;
    } else if (insertValue == 1) {
        fprintf(fp, "Something wrong, the entry exists but didnt show up in st_lookup\n");
        return(NULL);
    }

    if (Cudd_IsComplement(node)) {
        nodeStat->oddTopDist = 0;
    } else {
        nodeStat->evenTopDist = 0;
    }
    numParents = 1;
    /* call the function that counts the distance of each node from the
     * root
     */
#ifdef DD_DEBUG
    numCalls = 0;
#endif
    CreateTopDist(pathTable, parentPage, parentQueueIndex, (int) topLen,
                  childPage, childQueueIndex, numParents, fp);
    if (memOut) {
        fprintf(fp, "Out of Memory and cant count path lengths\n");
        goto OUT_OF_MEM;
    }

#ifdef DD_DEBUG
    numCalls = 0;
#endif
    /* call the function that counts the distance of each node from the
     * constant
     */
    if (!CreateBotDist(node, pathTable, pathLengthArray, fp)) return(NULL);

    /* free BFS queue pages as no longer required */
    for (i = 0; i <= queuePage; i++) ABC_FREE(queuePages[i]);
    ABC_FREE(queuePages);
    return(pathTable);

OUT_OF_MEM:
    (void) fprintf(fp, "Out of Memory, cannot allocate pages\n");
    memOut = 1;
    return(NULL);

} /*end of CreatePathTable */


/**Function********************************************************************

  Synopsis    [Chooses the maximum allowable path length of nodes under the
  threshold.]

  Description [Chooses the maximum allowable path length under each node.
  The corner cases are when the threshold is larger than the number
  of nodes in the BDD iself, in which case 'numVars + 1' is returned.
  If all nodes of a particular path length are needed, then the
  maxpath returned is the next one with excess nodes = 0;]

  SideEffects [None]

  SeeAlso     []

******************************************************************************/
static unsigned int
AssessPathLength(
  unsigned int * pathLengthArray /* array determining number of nodes belonging to the different path lengths */,
  int  threshold /* threshold to determine maximum allowable nodes in the subset */,
  int  numVars /* maximum number of variables */,
  unsigned int * excess /* number of nodes labeled maxpath required in the subset */,
  FILE *fp /* where to write messages */)
{
    unsigned int i, maxpath;
    int temp;

    temp = threshold;
    i = 0;
    maxpath = 0;
    /* quit loop if i reaches max number of variables or if temp reaches
     * below zero
     */
    while ((i < (unsigned) numVars+1) && (temp > 0)) {
        if (pathLengthArray[i] > 0) {
            maxpath = i;
            temp = temp - pathLengthArray[i];
        }
        i++;
    }
    /* if all nodes of max path are needed */
    if (temp >= 0) {
        maxpath++; /* now maxpath  becomes the next maxppath or max number
                      of variables */
        *excess = 0;
    } else { /* normal case when subset required is less than size of
                original BDD */
        *excess = temp + pathLengthArray[maxpath];
    }

    if (maxpath == 0) {
        fprintf(fp, "Path Length array seems to be all zeroes, check\n");
    }
    return(maxpath);

} /* end of AssessPathLength */


/**Function********************************************************************

  Synopsis    [Builds the BDD with nodes labeled with path length less than or equal to maxpath]

  Description [Builds the BDD with nodes labeled with path length
  under maxpath and as many nodes labeled maxpath as determined by the
  threshold. The procedure uses the path table to determine which nodes
  in the original bdd need to be retained. This procedure picks a
  shortest path (tie break decided by taking the child with the shortest
  distance to the constant) and recurs down the path till it reaches the
  constant. the procedure then starts building the subset upward from
  the constant. All nodes labeled by path lengths less than the given
  maxpath are used to build the subset.  However, in the case of nodes
  that have label equal to maxpath, as many are chosen as required by
  the threshold. This number is stored in the info structure in the
  field thresholdReached. This field is decremented whenever a node
  labeled maxpath is encountered and the nodes labeled maxpath are
  aggregated in a maxpath table. As soon as the thresholdReached count
  goes to 0, the shortest path from this node to the constant is found.
  The extraction of nodes with the above labeling is based on the fact
  that each node, labeled with a path length, P, has at least one child
  labeled P or less. So extracting all nodes labeled a given path length
  P ensures complete paths between the root and the constant. Extraction
  of a partial number of nodes with a given path length may result in
  incomplete paths and hence the additional number of nodes are grabbed
  to complete the path. Since the Bdd is built bottom-up, other nodes
  labeled maxpath do lie on complete paths.  The procedure may cause the
  subset to have a larger or smaller number of nodes than the specified
  threshold. The increase in the number of nodes is caused by the
  building of a subset and the reduction by recombination. However in
  most cases, the recombination overshadows the increase and the
  procedure returns a result with lower number of nodes than specified.
  The subsetNodeTable is NIL when there is no hard limit on the number
  of nodes. Further efforts towards keeping the subset closer to the
  threshold number were abandoned in favour of keeping the procedure
  simple and fast.]

  SideEffects [SubsetNodeTable is changed if it is not NIL.]

  SeeAlso     []

******************************************************************************/
static DdNode *
BuildSubsetBdd(
  DdManager * dd /* DD manager */,
  st_table * pathTable /* path table with path lengths and computed results */,
  DdNode * node /* current node */,
  struct AssortedInfo * info /* assorted information structure */,
  st_table * subsetNodeTable /* table storing computed results */)
{
    DdNode *N, *Nv, *Nnv;
    DdNode *ThenBranch, *ElseBranch, *childBranch;
    DdNode *child, *regChild, *regNnv = NULL, *regNv = NULL;
    NodeDist_t *nodeStatNv, *nodeStat, *nodeStatNnv;
    DdNode *neW, *topv, *regNew;
    char *entry;
    unsigned int topid;
    unsigned int childPathLength, oddLen, evenLen, NnvPathLength = 0, NvPathLength = 0;
    unsigned int NvBotDist, NnvBotDist;
    int tiebreakChild;
    int  processingDone, thenDone, elseDone;


#ifdef DD_DEBUG
    numCalls++;
#endif
    if (Cudd_IsConstant(node))
        return(node);

    N = Cudd_Regular(node);
    /* Find node in table. */
    if (!st_lookup(pathTable, (const char *)N, (char **)&nodeStat)) {
        (void) fprintf(dd->err, "Something wrong, node must be in table \n");
        dd->errorCode = CUDD_INTERNAL_ERROR;
        return(NULL);
    }
    /* If the node in the table has been visited, then return the corresponding
    ** Dd. Since a node can become a subset of itself, its
    ** complement (that is te same node reached by a different parity) will
    ** become a superset of the original node and result in some minterms
    ** that were not in the original set. Hence two different results are
    ** maintained, corresponding to the odd and even parities.
    */

    /* If this node is reached with an odd parity, get odd parity results. */
    if (Cudd_IsComplement(node)) {
        if  (nodeStat->compResult != NULL) {
#ifdef DD_DEBUG
            hits++;
#endif
            return(nodeStat->compResult);
        }
    } else {
        /* if this node is reached with an even parity, get even parity
         * results
         */
        if (nodeStat->regResult != NULL) {
#ifdef DD_DEBUG
            hits++;
#endif
            return(nodeStat->regResult);
        }
    }


    /* get children */
    Nv = Cudd_T(N);
    Nnv = Cudd_E(N);

    Nv = Cudd_NotCond(Nv, Cudd_IsComplement(node));
    Nnv = Cudd_NotCond(Nnv, Cudd_IsComplement(node));

    /* no child processed */
    processingDone = 0;
    /* then child not processed */
    thenDone = 0;
    ThenBranch = NULL;
    /* else child not processed */
    elseDone = 0;
    ElseBranch = NULL;
    /* if then child constant, branch is the child */
    if (Cudd_IsConstant(Nv)) {
        /*shortest path found */
        if ((Nv == DD_ONE(dd)) && (info->findShortestPath)) {
            info->findShortestPath = 0;
        }

        ThenBranch = Nv;
        cuddRef(ThenBranch);
        if (ThenBranch == NULL) {
            return(NULL);
        }

        thenDone++;
        processingDone++;
        NvBotDist = MAXSHORTINT;
    } else {
        /* Derive regular child for table lookup. */
        regNv = Cudd_Regular(Nv);
        /* Get node data for shortest path length. */
        if (!st_lookup(pathTable, (const char *)regNv, (char **)&nodeStatNv) ) {
            (void) fprintf(dd->err, "Something wrong, node must be in table\n");
            dd->errorCode = CUDD_INTERNAL_ERROR;
            return(NULL);
        }
        /* Derive shortest path length for child. */
        if ((nodeStatNv->oddTopDist != MAXSHORTINT) &&
            (nodeStatNv->oddBotDist != MAXSHORTINT)) {
            oddLen = (nodeStatNv->oddTopDist + nodeStatNv->oddBotDist);
        } else {
            oddLen = MAXSHORTINT;
        }

        if ((nodeStatNv->evenTopDist != MAXSHORTINT) &&
            (nodeStatNv->evenBotDist != MAXSHORTINT)) {
            evenLen = (nodeStatNv->evenTopDist +nodeStatNv->evenBotDist);
        } else {
            evenLen = MAXSHORTINT;
        }

        NvPathLength = (oddLen <= evenLen) ? oddLen : evenLen;
        NvBotDist = (oddLen <= evenLen) ? nodeStatNv->oddBotDist:
                                                   nodeStatNv->evenBotDist;
    }
    /* if else child constant, branch is the child */
    if (Cudd_IsConstant(Nnv)) {
        /*shortest path found */
        if ((Nnv == DD_ONE(dd)) && (info->findShortestPath)) {
            info->findShortestPath = 0;
        }

        ElseBranch = Nnv;
        cuddRef(ElseBranch);
        if (ElseBranch == NULL) {
            return(NULL);
        }

        elseDone++;
        processingDone++;
        NnvBotDist = MAXSHORTINT;
    } else {
        /* Derive regular child for table lookup. */
        regNnv = Cudd_Regular(Nnv);
        /* Get node data for shortest path length. */
        if (!st_lookup(pathTable, (const char *)regNnv, (char **)&nodeStatNnv) ) {
            (void) fprintf(dd->err, "Something wrong, node must be in table\n");
            dd->errorCode = CUDD_INTERNAL_ERROR;
            return(NULL);
        }
        /* Derive shortest path length for child. */
        if ((nodeStatNnv->oddTopDist != MAXSHORTINT) &&
            (nodeStatNnv->oddBotDist != MAXSHORTINT)) {
            oddLen = (nodeStatNnv->oddTopDist + nodeStatNnv->oddBotDist);
        } else {
            oddLen = MAXSHORTINT;
        }

        if ((nodeStatNnv->evenTopDist != MAXSHORTINT) &&
            (nodeStatNnv->evenBotDist != MAXSHORTINT)) {
            evenLen = (nodeStatNnv->evenTopDist +nodeStatNnv->evenBotDist);
        } else {
            evenLen = MAXSHORTINT;
        }

        NnvPathLength = (oddLen <= evenLen) ? oddLen : evenLen;
        NnvBotDist = (oddLen <= evenLen) ? nodeStatNnv->oddBotDist :
                                                   nodeStatNnv->evenBotDist;
    }

    tiebreakChild = (NvBotDist <= NnvBotDist) ? 1 : 0;
    /* while both children not processed */
    while (processingDone != 2) {
        if (!processingDone) {
            /* if no child processed */
            /* pick the child with shortest path length and record which one
             * picked
             */
            if ((NvPathLength < NnvPathLength) ||
                ((NvPathLength == NnvPathLength) && (tiebreakChild == 1))) {
                child = Nv;
                regChild = regNv;
                thenDone = 1;
                childPathLength = NvPathLength;
            } else {
                child = Nnv;
                regChild = regNnv;
                elseDone = 1;
                childPathLength = NnvPathLength;
            } /* then path length less than else path length */
        } else {
            /* if one child processed, process the other */
            if (thenDone) {
                child = Nnv;
                regChild = regNnv;
                elseDone = 1;
                childPathLength = NnvPathLength;
            } else {
                child = Nv;
                regChild = regNv;
                thenDone = 1;
                childPathLength = NvPathLength;
            } /* end of else pick the Then child if ELSE child processed */
        } /* end of else one child has been processed */

        /* ignore (replace with constant 0) all nodes which lie on paths larger
         * than the maximum length of the path required
         */
        if (childPathLength > info->maxpath) {
            /* record nodes visited */
            childBranch = zero;
        } else {
            if (childPathLength < info->maxpath) {
                if (info->findShortestPath) {
                    info->findShortestPath = 0;
                }
                childBranch = BuildSubsetBdd(dd, pathTable, child, info,
                                             subsetNodeTable);

            } else { /* Case: path length of node = maxpath */
                /* If the node labeled with maxpath is found in the
                ** maxpathTable, use it to build the subset BDD.  */
                if (st_lookup(info->maxpathTable, (char *)regChild,
                              (char **)&entry)) {
                    /* When a node that is already been chosen is hit,
                    ** the quest for a complete path is over.  */
                    if (info->findShortestPath) {
                        info->findShortestPath = 0;
                    }
                    childBranch = BuildSubsetBdd(dd, pathTable, child, info,
                                                 subsetNodeTable);
                } else {
                    /* If node is not found in the maxpathTable and
                    ** the threshold has been reached, then if the
                    ** path needs to be completed, continue. Else
                    ** replace the node with a zero.  */
                    if (info->thresholdReached <= 0) {
                        if (info->findShortestPath) {
                            if (st_insert(info->maxpathTable, (char *)regChild,
                                          (char *)NIL(char)) == ST_OUT_OF_MEM) {
                                memOut = 1;
                                (void) fprintf(dd->err, "OUT of memory\n");
                                info->thresholdReached = 0;
                                childBranch = zero;
                            } else {
                                info->thresholdReached--;
                                childBranch = BuildSubsetBdd(dd, pathTable,
                                                    child, info,subsetNodeTable);
                            }
                        } else { /* not find shortest path, we dont need this
                                    node */
                            childBranch = zero;
                        }
                    } else { /* Threshold hasn't been reached,
                             ** need the node. */
                        if (st_insert(info->maxpathTable, (char *)regChild,
                                      (char *)NIL(char)) == ST_OUT_OF_MEM) {
                            memOut = 1;
                            (void) fprintf(dd->err, "OUT of memory\n");
                            info->thresholdReached = 0;
                            childBranch = zero;
                        } else {
                            info->thresholdReached--;
                            if (info->thresholdReached <= 0) {
                                info->findShortestPath = 1;
                            }
                            childBranch = BuildSubsetBdd(dd, pathTable,
                                                 child, info, subsetNodeTable);

                        } /* end of st_insert successful */
                    } /* end of threshold hasnt been reached yet */
                } /* end of else node not found in maxpath table */
            } /* end of if (path length of node = maxpath) */
        } /* end if !(childPathLength > maxpath) */
        if (childBranch == NULL) {
            /* deref other stuff incase reordering has taken place */
            if (ThenBranch != NULL) {
                Cudd_RecursiveDeref(dd, ThenBranch);
                ThenBranch = NULL;
            }
            if (ElseBranch != NULL) {
                Cudd_RecursiveDeref(dd, ElseBranch);
                ElseBranch = NULL;
            }
            return(NULL);
        }

        cuddRef(childBranch);

        if (child == Nv) {
            ThenBranch = childBranch;
        } else {
            ElseBranch = childBranch;
        }
        processingDone++;

    } /*end of while processing Nv, Nnv */

    info->findShortestPath = 0;
    topid = Cudd_NodeReadIndex(N);
    topv = Cudd_ReadVars(dd, topid);
    cuddRef(topv);
    neW = cuddBddIteRecur(dd, topv, ThenBranch, ElseBranch);
    if (neW != NULL) {
        cuddRef(neW);
    }
    Cudd_RecursiveDeref(dd, topv);
    Cudd_RecursiveDeref(dd, ThenBranch);
    Cudd_RecursiveDeref(dd, ElseBranch);


    /* Hard Limit of threshold has been imposed */
    if (subsetNodeTable != NIL(st_table)) {
        /* check if a new node is created */
        regNew = Cudd_Regular(neW);
        /* subset node table keeps all new nodes that have been created to keep
         * a running count of how many nodes have been built in the subset.
         */
        if (!st_lookup(subsetNodeTable, (char *)regNew, (char **)&entry)) {
            if (!Cudd_IsConstant(regNew)) {
                if (st_insert(subsetNodeTable, (char *)regNew,
                              (char *)NULL) == ST_OUT_OF_MEM) {
                    (void) fprintf(dd->err, "Out of memory\n");
                    return (NULL);
                }
                if (st_count(subsetNodeTable) > info->threshold) {
                    info->thresholdReached = 0;
                }
            }
        }
    }


    if (neW == NULL) {
        return(NULL);
    } else {
        /*store computed result in regular form*/
        if (Cudd_IsComplement(node)) {
            nodeStat->compResult = neW;
            cuddRef(nodeStat->compResult);
            /* if the new node is the same as the corresponding node in the
             * original bdd then its complement need not be computed as it
             * cannot be larger than the node itself
             */
            if (neW == node) {
#ifdef DD_DEBUG
                thishit++;
#endif
                /* if a result for the node has already been computed, then
                 * it can only be smaller than teh node itself. hence store
                 * the node result in order not to break recombination
                 */
                if (nodeStat->regResult != NULL) {
                    Cudd_RecursiveDeref(dd, nodeStat->regResult);
                }
                nodeStat->regResult = Cudd_Not(neW);
                cuddRef(nodeStat->regResult);
            }

        } else {
            nodeStat->regResult = neW;
            cuddRef(nodeStat->regResult);
            if (neW == node) {
#ifdef DD_DEBUG
                thishit++;
#endif
                if (nodeStat->compResult != NULL) {
                    Cudd_RecursiveDeref(dd, nodeStat->compResult);
                }
                nodeStat->compResult = Cudd_Not(neW);
                cuddRef(nodeStat->compResult);
            }
        }

        cuddDeref(neW);
        return(neW);
    } /* end of else i.e. Subset != NULL */
} /* end of BuildSubsetBdd */


/**Function********************************************************************

  Synopsis     [Procedure to free te result dds stored in the NodeDist pages.]

  Description [None]

  SideEffects [None]

  SeeAlso     []

******************************************************************************/
static enum st_retval
stPathTableDdFree(
  char * key,
  char * value,
  char * arg)
{
    NodeDist_t *nodeStat;
    DdManager *dd;

    nodeStat = (NodeDist_t *)value;
    dd = (DdManager *)arg;
    if (nodeStat->regResult != NULL) {
        Cudd_RecursiveDeref(dd, nodeStat->regResult);
    }
    if (nodeStat->compResult != NULL) {
        Cudd_RecursiveDeref(dd, nodeStat->compResult);
    }
    return(ST_CONTINUE);

} /* end of stPathTableFree */


ABC_NAMESPACE_IMPL_END