src/cuBdd/cuddZddGroup.c

Go to the documentation of this file.

#include "util.h"
#include "cuddInt.h"

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

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

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

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

#ifndef lint
static char rcsid[] DD_UNUSED = "$Id: cuddZddGroup.c,v 1.20 2009/02/19 16:25:36 fabio Exp $";
#endif

static  int     *entry;
extern  int     zddTotalNumberSwapping;
#ifdef DD_STATS
static  int     extsymmcalls;
static  int     extsymm;
static  int     secdiffcalls;
static  int     secdiff;
static  int     secdiffmisfire;
#endif
#ifdef DD_DEBUG
static  int     pr = 0; /* flag to enable printing while debugging */
                        /* by depositing a 1 into it */
#endif

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

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

static int zddTreeSiftingAux (DdManager *table, MtrNode *treenode, Cudd_ReorderingType method);
#ifdef DD_STATS
static int zddCountInternalMtrNodes (DdManager *table, MtrNode *treenode);
#endif
static int zddReorderChildren (DdManager *table, MtrNode *treenode, Cudd_ReorderingType method);
static void zddFindNodeHiLo (DdManager *table, MtrNode *treenode, int *lower, int *upper);
static int zddUniqueCompareGroup (int *ptrX, int *ptrY);
static int zddGroupSifting (DdManager *table, int lower, int upper);
static int zddGroupSiftingAux (DdManager *table, int x, int xLow, int xHigh);
static int zddGroupSiftingUp (DdManager *table, int y, int xLow, Move **moves);
static int zddGroupSiftingDown (DdManager *table, int x, int xHigh, Move **moves);
static int zddGroupMove (DdManager *table, int x, int y, Move **moves);
static int zddGroupMoveBackward (DdManager *table, int x, int y);
static int zddGroupSiftingBackward (DdManager *table, Move *moves, int size);
static void zddMergeGroups (DdManager *table, MtrNode *treenode, int low, int high);

/*---------------------------------------------------------------------------*/
/* Definition of exported functions                                          */
/*---------------------------------------------------------------------------*/


MtrNode *
Cudd_MakeZddTreeNode(
  DdManager * dd /* manager */,
  unsigned int  low /* index of the first group variable */,
  unsigned int  size /* number of variables in the group */,
  unsigned int  type /* MTR_DEFAULT or MTR_FIXED */)
{
    MtrNode *group;
    MtrNode *tree;
    unsigned int level;

    /* If the variable does not exist yet, the position is assumed to be
    ** the same as the index. Therefore, applications that rely on
    ** Cudd_bddNewVarAtLevel or Cudd_addNewVarAtLevel to create new
    ** variables have to create the variables before they group them.
    */
    level = (low < (unsigned int) dd->sizeZ) ? dd->permZ[low] : low;

    if (level + size - 1> (int) MTR_MAXHIGH)
        return(NULL);

    /* If the tree does not exist yet, create it. */
    tree = dd->treeZ;
    if (tree == NULL) {
        dd->treeZ = tree = Mtr_InitGroupTree(0, dd->sizeZ);
        if (tree == NULL)
            return(NULL);
        tree->index = dd->invpermZ[0];
    }

    /* Extend the upper bound of the tree if necessary. This allows the
    ** application to create groups even before the variables are created.
    */
    tree->size = ddMax(tree->size, level + size);

    /* Create the group. */
    group = Mtr_MakeGroup(tree, level, size, type);
    if (group == NULL)
        return(NULL);

    /* Initialize the index field to the index of the variable currently
    ** in position low. This field will be updated by the reordering
    ** procedure to provide a handle to the group once it has been moved.
    */
    group->index = (MtrHalfWord) low;

    return(group);

} /* end of Cudd_MakeZddTreeNode */


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


int
cuddZddTreeSifting(
  DdManager * table /* DD table */,
  Cudd_ReorderingType method /* reordering method for the groups of leaves */)
{
    int i;
    int nvars;
    int result;
    int tempTree;

    /* If no tree is provided we create a temporary one in which all
    ** variables are in a single group. After reordering this tree is
    ** destroyed.
    */
    tempTree = table->treeZ == NULL;
    if (tempTree) {
        table->treeZ = Mtr_InitGroupTree(0,table->sizeZ);
        table->treeZ->index = table->invpermZ[0];
    }
    nvars = table->sizeZ;

#ifdef DD_DEBUG
    if (pr > 0 && !tempTree)
        (void) fprintf(table->out,"cuddZddTreeSifting:");
    Mtr_PrintGroups(table->treeZ,pr <= 0);
#endif
#if 0
    /* Debugging code. */
    if (table->tree && table->treeZ) {
        (void) fprintf(table->out,"\n");
        Mtr_PrintGroups(table->tree, 0);
        cuddPrintVarGroups(table,table->tree,0,0);
        for (i = 0; i < table->size; i++) {
            (void) fprintf(table->out,"%s%d",
                           (i == 0) ? "" : ",", table->invperm[i]);
        }
        (void) fprintf(table->out,"\n");
        for (i = 0; i < table->size; i++) {
            (void) fprintf(table->out,"%s%d",
                           (i == 0) ? "" : ",", table->perm[i]);
        }
        (void) fprintf(table->out,"\n\n");
        Mtr_PrintGroups(table->treeZ,0);
        cuddPrintVarGroups(table,table->treeZ,1,0);
        for (i = 0; i < table->sizeZ; i++) {
            (void) fprintf(table->out,"%s%d",
                           (i == 0) ? "" : ",", table->invpermZ[i]);
        }
        (void) fprintf(table->out,"\n");
        for (i = 0; i < table->sizeZ; i++) {
            (void) fprintf(table->out,"%s%d",
                           (i == 0) ? "" : ",", table->permZ[i]);
        }
        (void) fprintf(table->out,"\n");
    }
    /* End of debugging code. */
#endif
#ifdef DD_STATS
    extsymmcalls = 0;
    extsymm = 0;
    secdiffcalls = 0;
    secdiff = 0;
    secdiffmisfire = 0;

    (void) fprintf(table->out,"\n");
    if (!tempTree)
        (void) fprintf(table->out,"#:IM_NODES  %8d: group tree nodes\n",
                       zddCountInternalMtrNodes(table,table->treeZ));
#endif

    /* Initialize the group of each subtable to itself. Initially
    ** there are no groups. Groups are created according to the tree
    ** structure in postorder fashion.
    */
    for (i = 0; i < nvars; i++)
        table->subtableZ[i].next = i;

    /* Reorder. */
    result = zddTreeSiftingAux(table, table->treeZ, method);

#ifdef DD_STATS         /* print stats */
    if (!tempTree && method == CUDD_REORDER_GROUP_SIFT &&
        (table->groupcheck == CUDD_GROUP_CHECK7 ||
         table->groupcheck == CUDD_GROUP_CHECK5)) {
        (void) fprintf(table->out,"\nextsymmcalls = %d\n",extsymmcalls);
        (void) fprintf(table->out,"extsymm = %d",extsymm);
    }
    if (!tempTree && method == CUDD_REORDER_GROUP_SIFT &&
        table->groupcheck == CUDD_GROUP_CHECK7) {
        (void) fprintf(table->out,"\nsecdiffcalls = %d\n",secdiffcalls);
        (void) fprintf(table->out,"secdiff = %d\n",secdiff);
        (void) fprintf(table->out,"secdiffmisfire = %d",secdiffmisfire);
    }
#endif

    if (tempTree)
        Cudd_FreeZddTree(table);
    return(result);

} /* end of cuddZddTreeSifting */


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


static int
zddTreeSiftingAux(
  DdManager * table,
  MtrNode * treenode,
  Cudd_ReorderingType method)
{
    MtrNode  *auxnode;
    int res;

#ifdef DD_DEBUG
    Mtr_PrintGroups(treenode,1);
#endif

    auxnode = treenode;
    while (auxnode != NULL) {
        if (auxnode->child != NULL) {
            if (!zddTreeSiftingAux(table, auxnode->child, method))
                return(0);
            res = zddReorderChildren(table, auxnode, CUDD_REORDER_GROUP_SIFT);
            if (res == 0)
                return(0);
        } else if (auxnode->size > 1) {
            if (!zddReorderChildren(table, auxnode, method))
                return(0);
        }
        auxnode = auxnode->younger;
    }

    return(1);

} /* end of zddTreeSiftingAux */


#ifdef DD_STATS

static int
zddCountInternalMtrNodes(
  DdManager * table,
  MtrNode * treenode)
{
    MtrNode *auxnode;
    int     count,nodeCount;


    nodeCount = 0;
    auxnode = treenode;
    while (auxnode != NULL) {
        if (!(MTR_TEST(auxnode,MTR_TERMINAL))) {
            nodeCount++;
            count = zddCountInternalMtrNodes(table,auxnode->child);
            nodeCount += count;
        }
        auxnode = auxnode->younger;
    }

    return(nodeCount);

} /* end of zddCountInternalMtrNodes */
#endif


static int
zddReorderChildren(
  DdManager * table,
  MtrNode * treenode,
  Cudd_ReorderingType method)
{
    int lower;
    int upper;
    int result;
    unsigned int initialSize;

    zddFindNodeHiLo(table,treenode,&lower,&upper);
    /* If upper == -1 these variables do not exist yet. */
    if (upper == -1)
        return(1);

    if (treenode->flags == MTR_FIXED) {
        result = 1;
    } else {
#ifdef DD_STATS
        (void) fprintf(table->out," ");
#endif
        switch (method) {
        case CUDD_REORDER_RANDOM:
        case CUDD_REORDER_RANDOM_PIVOT:
            result = cuddZddSwapping(table,lower,upper,method);
            break;
        case CUDD_REORDER_SIFT:
            result = cuddZddSifting(table,lower,upper);
            break;
        case CUDD_REORDER_SIFT_CONVERGE:
            do {
                initialSize = table->keysZ;
                result = cuddZddSifting(table,lower,upper);
                if (initialSize <= table->keysZ)
                    break;
#ifdef DD_STATS
                else
                    (void) fprintf(table->out,"\n");
#endif
            } while (result != 0);
            break;
        case CUDD_REORDER_SYMM_SIFT:
            result = cuddZddSymmSifting(table,lower,upper);
            break;
        case CUDD_REORDER_SYMM_SIFT_CONV:
            result = cuddZddSymmSiftingConv(table,lower,upper);
            break;
        case CUDD_REORDER_GROUP_SIFT:
            result = zddGroupSifting(table,lower,upper);
            break;
        case CUDD_REORDER_LINEAR:
            result = cuddZddLinearSifting(table,lower,upper);
            break;
        case CUDD_REORDER_LINEAR_CONVERGE:
            do {
                initialSize = table->keysZ;
                result = cuddZddLinearSifting(table,lower,upper);
                if (initialSize <= table->keysZ)
                    break;
#ifdef DD_STATS
                else
                    (void) fprintf(table->out,"\n");
#endif
            } while (result != 0);
            break;
        default:
            return(0);
        }
    }

    /* Create a single group for all the variables that were sifted,
    ** so that they will be treated as a single block by successive
    ** invocations of zddGroupSifting.
    */
    zddMergeGroups(table,treenode,lower,upper);

#ifdef DD_DEBUG
    if (pr > 0) (void) fprintf(table->out,"zddReorderChildren:");
#endif

    return(result);

} /* end of zddReorderChildren */


static void
zddFindNodeHiLo(
  DdManager * table,
  MtrNode * treenode,
  int * lower,
  int * upper)
{
    int low;
    int high;

    /* Check whether no variables in this group already exist.
    ** If so, return immediately. The calling procedure will know from
    ** the values of upper that no reordering is needed.
    */
    if ((int) treenode->low >= table->sizeZ) {
        *lower = table->sizeZ;
        *upper = -1;
        return;
    }

    *lower = low = (unsigned int) table->permZ[treenode->index];
    high = (int) (low + treenode->size - 1);

    if (high >= table->sizeZ) {
        /* This is the case of a partially existing group. The aim is to
        ** reorder as many variables as safely possible.  If the tree
        ** node is terminal, we just reorder the subset of the group
        ** that is currently in existence.  If the group has
        ** subgroups, then we only reorder those subgroups that are
        ** fully instantiated.  This way we avoid breaking up a group.
        */
        MtrNode *auxnode = treenode->child;
        if (auxnode == NULL) {
            *upper = (unsigned int) table->sizeZ - 1;
        } else {
            /* Search the subgroup that strands the table->sizeZ line.
            ** If the first group starts at 0 and goes past table->sizeZ
            ** upper will get -1, thus correctly signaling that no reordering
            ** should take place.
            */
            while (auxnode != NULL) {
                int thisLower = table->permZ[auxnode->low];
                int thisUpper = thisLower + auxnode->size - 1;
                if (thisUpper >= table->sizeZ && thisLower < table->sizeZ)
                    *upper = (unsigned int) thisLower - 1;
                auxnode = auxnode->younger;
            }
        }
    } else {
        /* Normal case: All the variables of the group exist. */
        *upper = (unsigned int) high;
    }

#ifdef DD_DEBUG
    /* Make sure that all variables in group are contiguous. */
    assert(treenode->size >= *upper - *lower + 1);
#endif

    return;

} /* end of zddFindNodeHiLo */


static int
zddUniqueCompareGroup(
  int * ptrX,
  int * ptrY)
{
#if 0
    if (entry[*ptrY] == entry[*ptrX]) {
        return((*ptrX) - (*ptrY));
    }
#endif
    return(entry[*ptrY] - entry[*ptrX]);

} /* end of zddUniqueCompareGroup */


static int
zddGroupSifting(
  DdManager * table,
  int  lower,
  int  upper)
{
    int         *var;
    int         i,j,x,xInit;
    int         nvars;
    int         classes;
    int         result;
    int         *sifted;
#ifdef DD_STATS
    unsigned    previousSize;
#endif
    int         xindex;

    nvars = table->sizeZ;

    /* Order variables to sift. */
    entry = NULL;
    sifted = NULL;
    var = ALLOC(int,nvars);
    if (var == NULL) {
        table->errorCode = CUDD_MEMORY_OUT;
        goto zddGroupSiftingOutOfMem;
    }
    entry = ALLOC(int,nvars);
    if (entry == NULL) {
        table->errorCode = CUDD_MEMORY_OUT;
        goto zddGroupSiftingOutOfMem;
    }
    sifted = ALLOC(int,nvars);
    if (sifted == NULL) {
        table->errorCode = CUDD_MEMORY_OUT;
        goto zddGroupSiftingOutOfMem;
    }

    /* Here we consider only one representative for each group. */
    for (i = 0, classes = 0; i < nvars; i++) {
        sifted[i] = 0;
        x = table->permZ[i];
        if ((unsigned) x >= table->subtableZ[x].next) {
            entry[i] = table->subtableZ[x].keys;
            var[classes] = i;
            classes++;
        }
    }

    qsort((void *)var,classes,sizeof(int),(DD_QSFP)zddUniqueCompareGroup);

    /* Now sift. */
    for (i = 0; i < ddMin(table->siftMaxVar,classes); i++) {
        if (zddTotalNumberSwapping >= table->siftMaxSwap)
            break;
        xindex = var[i];
        if (sifted[xindex] == 1) /* variable already sifted as part of group */
            continue;
        x = table->permZ[xindex]; /* find current level of this variable */
        if (x < lower || x > upper)
            continue;
#ifdef DD_STATS
        previousSize = table->keysZ;
#endif
#ifdef DD_DEBUG
        /* x is bottom of group */
        assert((unsigned) x >= table->subtableZ[x].next);
#endif
        result = zddGroupSiftingAux(table,x,lower,upper);
        if (!result) goto zddGroupSiftingOutOfMem;

#ifdef DD_STATS
        if (table->keysZ < previousSize) {
            (void) fprintf(table->out,"-");
        } else if (table->keysZ > previousSize) {
            (void) fprintf(table->out,"+");
        } else {
            (void) fprintf(table->out,"=");
        }
        fflush(table->out);
#endif

        /* Mark variables in the group just sifted. */
        x = table->permZ[xindex];
        if ((unsigned) x != table->subtableZ[x].next) {
            xInit = x;
            do {
                j = table->invpermZ[x];
                sifted[j] = 1;
                x = table->subtableZ[x].next;
            } while (x != xInit);
        }

#ifdef DD_DEBUG
        if (pr > 0) (void) fprintf(table->out,"zddGroupSifting:");
#endif
    } /* for */

    FREE(sifted);
    FREE(var);
    FREE(entry);

    return(1);

zddGroupSiftingOutOfMem:
    if (entry != NULL)  FREE(entry);
    if (var != NULL)    FREE(var);
    if (sifted != NULL) FREE(sifted);

    return(0);

} /* end of zddGroupSifting */


static int
zddGroupSiftingAux(
  DdManager * table,
  int  x,
  int  xLow,
  int  xHigh)
{
    Move *move;
    Move *moves;        /* list of moves */
    int  initialSize;
    int  result;


#ifdef DD_DEBUG
    if (pr > 0) (void) fprintf(table->out,"zddGroupSiftingAux from %d to %d\n",xLow,xHigh);
    assert((unsigned) x >= table->subtableZ[x].next); /* x is bottom of group */
#endif

    initialSize = table->keysZ;
    moves = NULL;

    if (x == xLow) { /* Sift down */
#ifdef DD_DEBUG
        /* x must be a singleton */
        assert((unsigned) x == table->subtableZ[x].next);
#endif
        if (x == xHigh) return(1);      /* just one variable */

        if (!zddGroupSiftingDown(table,x,xHigh,&moves))
            goto zddGroupSiftingAuxOutOfMem;
        /* at this point x == xHigh, unless early term */

        /* move backward and stop at best position */
        result = zddGroupSiftingBackward(table,moves,initialSize);
#ifdef DD_DEBUG
        assert(table->keysZ <= (unsigned) initialSize);
#endif
        if (!result) goto zddGroupSiftingAuxOutOfMem;

    } else if (cuddZddNextHigh(table,x) > xHigh) { /* Sift up */
#ifdef DD_DEBUG
        /* x is bottom of group */
        assert((unsigned) x >= table->subtableZ[x].next);
#endif
        /* Find top of x's group */
        x = table->subtableZ[x].next;

        if (!zddGroupSiftingUp(table,x,xLow,&moves))
            goto zddGroupSiftingAuxOutOfMem;
        /* at this point x == xLow, unless early term */

        /* move backward and stop at best position */
        result = zddGroupSiftingBackward(table,moves,initialSize);
#ifdef DD_DEBUG
        assert(table->keysZ <= (unsigned) initialSize);
#endif
        if (!result) goto zddGroupSiftingAuxOutOfMem;

    } else if (x - xLow > xHigh - x) { /* must go down first: shorter */
        if (!zddGroupSiftingDown(table,x,xHigh,&moves))
            goto zddGroupSiftingAuxOutOfMem;
        /* at this point x == xHigh, unless early term */

        /* Find top of group */
        if (moves) {
            x = moves->y;
        }
        while ((unsigned) x < table->subtableZ[x].next)
            x = table->subtableZ[x].next;
        x = table->subtableZ[x].next;
#ifdef DD_DEBUG
        /* x should be the top of a group */
        assert((unsigned) x <= table->subtableZ[x].next);
#endif

        if (!zddGroupSiftingUp(table,x,xLow,&moves))
            goto zddGroupSiftingAuxOutOfMem;

        /* move backward and stop at best position */
        result = zddGroupSiftingBackward(table,moves,initialSize);
#ifdef DD_DEBUG
        assert(table->keysZ <= (unsigned) initialSize);
#endif
        if (!result) goto zddGroupSiftingAuxOutOfMem;

    } else { /* moving up first: shorter */
        /* Find top of x's group */
        x = table->subtableZ[x].next;

        if (!zddGroupSiftingUp(table,x,xLow,&moves))
            goto zddGroupSiftingAuxOutOfMem;
        /* at this point x == xHigh, unless early term */

        if (moves) {
            x = moves->x;
        }
        while ((unsigned) x < table->subtableZ[x].next)
            x = table->subtableZ[x].next;
#ifdef DD_DEBUG
        /* x is bottom of a group */
        assert((unsigned) x >= table->subtableZ[x].next);
#endif

        if (!zddGroupSiftingDown(table,x,xHigh,&moves))
            goto zddGroupSiftingAuxOutOfMem;

        /* move backward and stop at best position */
        result = zddGroupSiftingBackward(table,moves,initialSize);
#ifdef DD_DEBUG
        assert(table->keysZ <= (unsigned) initialSize);
#endif
        if (!result) goto zddGroupSiftingAuxOutOfMem;
    }

    while (moves != NULL) {
        move = moves->next;
        cuddDeallocMove(table, moves);
        moves = move;
    }

    return(1);

zddGroupSiftingAuxOutOfMem:
    while (moves != NULL) {
        move = moves->next;
        cuddDeallocMove(table, moves);
        moves = move;
    }

    return(0);

} /* end of zddGroupSiftingAux */


static int
zddGroupSiftingUp(
  DdManager * table,
  int  y,
  int  xLow,
  Move ** moves)
{
    Move *move;
    int  x;
    int  size;
    int  gxtop;
    int  limitSize;

    limitSize = table->keysZ;

    x = cuddZddNextLow(table,y);
    while (x >= xLow) {
        gxtop = table->subtableZ[x].next;
        if (table->subtableZ[x].next == (unsigned) x &&
            table->subtableZ[y].next == (unsigned) y) {
            /* x and y are self groups */
            size = cuddZddSwapInPlace(table,x,y);
#ifdef DD_DEBUG
            assert(table->subtableZ[x].next == (unsigned) x);
            assert(table->subtableZ[y].next == (unsigned) y);
#endif
            if (size == 0) goto zddGroupSiftingUpOutOfMem;
            move = (Move *)cuddDynamicAllocNode(table);
            if (move == NULL) goto zddGroupSiftingUpOutOfMem;
            move->x = x;
            move->y = y;
            move->flags = MTR_DEFAULT;
            move->size = size;
            move->next = *moves;
            *moves = move;

#ifdef DD_DEBUG
            if (pr > 0) (void) fprintf(table->out,"zddGroupSiftingUp (2 single groups):\n");
#endif
            if ((double) size > (double) limitSize * table->maxGrowth)
                return(1);
            if (size < limitSize) limitSize = size;
        } else { /* group move */
            size = zddGroupMove(table,x,y,moves);
            if (size == 0) goto zddGroupSiftingUpOutOfMem;
            if ((double) size > (double) limitSize * table->maxGrowth)
                return(1);
            if (size < limitSize) limitSize = size;
        }
        y = gxtop;
        x = cuddZddNextLow(table,y);
    }

    return(1);

zddGroupSiftingUpOutOfMem:
    while (*moves != NULL) {
        move = (*moves)->next;
        cuddDeallocMove(table, *moves);
        *moves = move;
    }
    return(0);

} /* end of zddGroupSiftingUp */


static int
zddGroupSiftingDown(
  DdManager * table,
  int  x,
  int  xHigh,
  Move ** moves)
{
    Move *move;
    int  y;
    int  size;
    int  limitSize;
    int  gybot;


    /* Initialize R */
    limitSize = size = table->keysZ;
    y = cuddZddNextHigh(table,x);
    while (y <= xHigh) {
        /* Find bottom of y group. */
        gybot = table->subtableZ[y].next;
        while (table->subtableZ[gybot].next != (unsigned) y)
            gybot = table->subtableZ[gybot].next;

        if (table->subtableZ[x].next == (unsigned) x &&
            table->subtableZ[y].next == (unsigned) y) {
            /* x and y are self groups */
            size = cuddZddSwapInPlace(table,x,y);
#ifdef DD_DEBUG
            assert(table->subtableZ[x].next == (unsigned) x);
            assert(table->subtableZ[y].next == (unsigned) y);
#endif
            if (size == 0) goto zddGroupSiftingDownOutOfMem;

            /* Record move. */
            move = (Move *) cuddDynamicAllocNode(table);
            if (move == NULL) goto zddGroupSiftingDownOutOfMem;
            move->x = x;
            move->y = y;
            move->flags = MTR_DEFAULT;
            move->size = size;
            move->next = *moves;
            *moves = move;

#ifdef DD_DEBUG
            if (pr > 0) (void) fprintf(table->out,"zddGroupSiftingDown (2 single groups):\n");
#endif
            if ((double) size > (double) limitSize * table->maxGrowth)
                return(1);
            if (size < limitSize) limitSize = size;
            x = y;
            y = cuddZddNextHigh(table,x);
        } else { /* Group move */
            size = zddGroupMove(table,x,y,moves);
            if (size == 0) goto zddGroupSiftingDownOutOfMem;
            if ((double) size > (double) limitSize * table->maxGrowth)
                return(1);
            if (size < limitSize) limitSize = size;
        }
        x = gybot;
        y = cuddZddNextHigh(table,x);
    }

    return(1);

zddGroupSiftingDownOutOfMem:
    while (*moves != NULL) {
        move = (*moves)->next;
        cuddDeallocMove(table, *moves);
        *moves = move;
    }

    return(0);

} /* end of zddGroupSiftingDown */


static int
zddGroupMove(
  DdManager * table,
  int  x,
  int  y,
  Move ** moves)
{
    Move *move;
    int  size;
    int  i,j,xtop,xbot,xsize,ytop,ybot,ysize,newxtop;
    int  swapx,swapy;
#if defined(DD_DEBUG) && defined(DD_VERBOSE)
    int  initialSize,bestSize;
#endif

#ifdef DD_DEBUG
    /* We assume that x < y */
    assert(x < y);
#endif
    /* Find top, bottom, and size for the two groups. */
    xbot = x;
    xtop = table->subtableZ[x].next;
    xsize = xbot - xtop + 1;
    ybot = y;
    while ((unsigned) ybot < table->subtableZ[ybot].next)
        ybot = table->subtableZ[ybot].next;
    ytop = y;
    ysize = ybot - ytop + 1;

#if defined(DD_DEBUG) && defined(DD_VERBOSE)
    initialSize = bestSize = table->keysZ;
#endif
    /* Sift the variables of the second group up through the first group */
    for (i = 1; i <= ysize; i++) {
        for (j = 1; j <= xsize; j++) {
            size = cuddZddSwapInPlace(table,x,y);
            if (size == 0) goto zddGroupMoveOutOfMem;
#if defined(DD_DEBUG) && defined(DD_VERBOSE)
            if (size < bestSize)
                bestSize = size;
#endif
            swapx = x; swapy = y;
            y = x;
            x = cuddZddNextLow(table,y);
        }
        y = ytop + i;
        x = cuddZddNextLow(table,y);
    }
#if defined(DD_DEBUG) && defined(DD_VERBOSE)
    if ((bestSize < initialSize) && (bestSize < size))
        (void) fprintf(table->out,"Missed local minimum: initialSize:%d  bestSize:%d  finalSize:%d\n",initialSize,bestSize,size);
#endif

    /* fix groups */
    y = xtop; /* ytop is now where xtop used to be */
    for (i = 0; i < ysize - 1; i++) {
        table->subtableZ[y].next = cuddZddNextHigh(table,y);
        y = cuddZddNextHigh(table,y);
    }
    table->subtableZ[y].next = xtop; /* y is bottom of its group, join */
                                    /* it to top of its group */
    x = cuddZddNextHigh(table,y);
    newxtop = x;
    for (i = 0; i < xsize - 1; i++) {
        table->subtableZ[x].next = cuddZddNextHigh(table,x);
        x = cuddZddNextHigh(table,x);
    }
    table->subtableZ[x].next = newxtop; /* x is bottom of its group, join */
                                    /* it to top of its group */
#ifdef DD_DEBUG
    if (pr > 0) (void) fprintf(table->out,"zddGroupMove:\n");
#endif

    /* Store group move */
    move = (Move *) cuddDynamicAllocNode(table);
    if (move == NULL) goto zddGroupMoveOutOfMem;
    move->x = swapx;
    move->y = swapy;
    move->flags = MTR_DEFAULT;
    move->size = table->keysZ;
    move->next = *moves;
    *moves = move;

    return(table->keysZ);

zddGroupMoveOutOfMem:
    while (*moves != NULL) {
        move = (*moves)->next;
        cuddDeallocMove(table, *moves);
        *moves = move;
    }
    return(0);

} /* end of zddGroupMove */


static int
zddGroupMoveBackward(
  DdManager * table,
  int  x,
  int  y)
{
    int size;
    int i,j,xtop,xbot,xsize,ytop,ybot,ysize,newxtop;


#ifdef DD_DEBUG
    /* We assume that x < y */
    assert(x < y);
#endif

    /* Find top, bottom, and size for the two groups. */
    xbot = x;
    xtop = table->subtableZ[x].next;
    xsize = xbot - xtop + 1;
    ybot = y;
    while ((unsigned) ybot < table->subtableZ[ybot].next)
        ybot = table->subtableZ[ybot].next;
    ytop = y;
    ysize = ybot - ytop + 1;

    /* Sift the variables of the second group up through the first group */
    for (i = 1; i <= ysize; i++) {
        for (j = 1; j <= xsize; j++) {
            size = cuddZddSwapInPlace(table,x,y);
            if (size == 0)
                return(0);
            y = x;
            x = cuddZddNextLow(table,y);
        }
        y = ytop + i;
        x = cuddZddNextLow(table,y);
    }

    /* fix groups */
    y = xtop;
    for (i = 0; i < ysize - 1; i++) {
        table->subtableZ[y].next = cuddZddNextHigh(table,y);
        y = cuddZddNextHigh(table,y);
    }
    table->subtableZ[y].next = xtop; /* y is bottom of its group, join */
                                    /* to its top */
    x = cuddZddNextHigh(table,y);
    newxtop = x;
    for (i = 0; i < xsize - 1; i++) {
        table->subtableZ[x].next = cuddZddNextHigh(table,x);
        x = cuddZddNextHigh(table,x);
    }
    table->subtableZ[x].next = newxtop; /* x is bottom of its group, join */
                                    /* to its top */
#ifdef DD_DEBUG
    if (pr > 0) (void) fprintf(table->out,"zddGroupMoveBackward:\n");
#endif

    return(1);

} /* end of zddGroupMoveBackward */


static int
zddGroupSiftingBackward(
  DdManager * table,
  Move * moves,
  int  size)
{
    Move *move;
    int  res;


    for (move = moves; move != NULL; move = move->next) {
        if (move->size < size) {
            size = move->size;
        }
    }

    for (move = moves; move != NULL; move = move->next) {
        if (move->size == size) return(1);
        if ((table->subtableZ[move->x].next == move->x) &&
        (table->subtableZ[move->y].next == move->y)) {
            res = cuddZddSwapInPlace(table,(int)move->x,(int)move->y);
            if (!res) return(0);
#ifdef DD_DEBUG
            if (pr > 0) (void) fprintf(table->out,"zddGroupSiftingBackward:\n");
            assert(table->subtableZ[move->x].next == move->x);
            assert(table->subtableZ[move->y].next == move->y);
#endif
        } else { /* Group move necessary */
            res = zddGroupMoveBackward(table,(int)move->x,(int)move->y);
            if (!res) return(0);
        }
    }

    return(1);

} /* end of zddGroupSiftingBackward */


static void
zddMergeGroups(
  DdManager * table,
  MtrNode * treenode,
  int  low,
  int  high)
{
    int i;
    MtrNode *auxnode;
    int saveindex;
    int newindex;

    /* Merge all variables from low to high in one group, unless
    ** this is the topmost group. In such a case we do not merge lest
    ** we lose the symmetry information. */
    if (treenode != table->treeZ) {
        for (i = low; i < high; i++)
            table->subtableZ[i].next = i+1;
        table->subtableZ[high].next = low;
    }

    /* Adjust the index fields of the tree nodes. If a node is the
    ** first child of its parent, then the parent may also need adjustment. */
    saveindex = treenode->index;
    newindex = table->invpermZ[low];
    auxnode = treenode;
    do {
        auxnode->index = newindex;
        if (auxnode->parent == NULL ||
                (int) auxnode->parent->index != saveindex)
            break;
        auxnode = auxnode->parent;
    } while (1);
    return;

} /* end of zddMergeGroups */

---