src/cuBdd/cuddSat.c

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

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

#define DD_BIGGY        1000000

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

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

typedef struct cuddPathPair {
    int pos;
    int neg;
} cuddPathPair;

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

#ifndef lint
static char rcsid[] DD_UNUSED = "$Id: cuddSat.c,v 1.36 2009/03/08 02:49:02 fabio Exp $";
#endif

static  DdNode  *one, *zero;

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

#define WEIGHT(weight, col)     ((weight) == NULL ? 1 : weight[col])

#ifdef __cplusplus
extern "C" {
#endif

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

static enum st_retval freePathPair (char *key, char *value, char *arg);
static cuddPathPair getShortest (DdNode *root, int *cost, int *support, st_table *visited);
static DdNode * getPath (DdManager *manager, st_table *visited, DdNode *f, int *weight, int cost);
static cuddPathPair getLargest (DdNode *root, st_table *visited);
static DdNode * getCube (DdManager *manager, st_table *visited, DdNode *f, int cost);

#ifdef __cplusplus
}
#endif

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


DdNode *
Cudd_Eval(
  DdManager * dd,
  DdNode * f,
  int * inputs)
{
    int comple;
    DdNode *ptr;

    comple = Cudd_IsComplement(f);
    ptr = Cudd_Regular(f);

    while (!cuddIsConstant(ptr)) {
        if (inputs[ptr->index] == 1) {
            ptr = cuddT(ptr);
        } else {
            comple ^= Cudd_IsComplement(cuddE(ptr));
            ptr = Cudd_Regular(cuddE(ptr));
        }
    }
    return(Cudd_NotCond(ptr,comple));

} /* end of Cudd_Eval */


DdNode *
Cudd_ShortestPath(
  DdManager * manager,
  DdNode * f,
  int * weight,
  int * support,
  int * length)
{
    DdNode      *F;
    st_table    *visited;
    DdNode      *sol;
    cuddPathPair *rootPair;
    int         complement, cost;
    int         i;

    one = DD_ONE(manager);
    zero = DD_ZERO(manager);

    /* Initialize support. Support does not depend on variable order.
    ** Hence, it does not need to be reinitialized if reordering occurs.
    */
    if (support) {
      for (i = 0; i < manager->size; i++) {
        support[i] = 0;
      }
    }

    if (f == Cudd_Not(one) || f == zero) {
      *length = DD_BIGGY;
      return(Cudd_Not(one));
    }
    /* From this point on, a path exists. */

    do {
        manager->reordered = 0;

        /* Initialize visited table. */
        visited = st_init_table(st_ptrcmp, st_ptrhash);

        /* Now get the length of the shortest path(s) from f to 1. */
        (void) getShortest(f, weight, support, visited);

        complement = Cudd_IsComplement(f);

        F = Cudd_Regular(f);

        if (!st_lookup(visited, F, &rootPair)) return(NULL);

        if (complement) {
          cost = rootPair->neg;
        } else {
          cost = rootPair->pos;
        }

        /* Recover an actual shortest path. */
        sol = getPath(manager,visited,f,weight,cost);

        st_foreach(visited, freePathPair, NULL);
        st_free_table(visited);

    } while (manager->reordered == 1);

    *length = cost;
    return(sol);

} /* end of Cudd_ShortestPath */


DdNode *
Cudd_LargestCube(
  DdManager * manager,
  DdNode * f,
  int * length)
{
    register    DdNode  *F;
    st_table    *visited;
    DdNode      *sol;
    cuddPathPair *rootPair;
    int         complement, cost;

    one = DD_ONE(manager);
    zero = DD_ZERO(manager);

    if (f == Cudd_Not(one) || f == zero) {
        *length = DD_BIGGY;
        return(Cudd_Not(one));
    }
    /* From this point on, a path exists. */

    do {
        manager->reordered = 0;

        /* Initialize visited table. */
        visited = st_init_table(st_ptrcmp, st_ptrhash);

        /* Now get the length of the shortest path(s) from f to 1. */
        (void) getLargest(f, visited);

        complement = Cudd_IsComplement(f);

        F = Cudd_Regular(f);

        if (!st_lookup(visited, F, &rootPair)) return(NULL);

        if (complement) {
          cost = rootPair->neg;
        } else {
          cost = rootPair->pos;
        }

        /* Recover an actual shortest path. */
        sol = getCube(manager,visited,f,cost);

        st_foreach(visited, freePathPair, NULL);
        st_free_table(visited);

    } while (manager->reordered == 1);

    *length = cost;
    return(sol);

} /* end of Cudd_LargestCube */


int
Cudd_ShortestLength(
  DdManager * manager,
  DdNode * f,
  int * weight)
{
    register    DdNode  *F;
    st_table    *visited;
    cuddPathPair *my_pair;
    int         complement, cost;

    one = DD_ONE(manager);
    zero = DD_ZERO(manager);

    if (f == Cudd_Not(one) || f == zero) {
        return(DD_BIGGY);
    }

    /* From this point on, a path exists. */
    /* Initialize visited table and support. */
    visited = st_init_table(st_ptrcmp, st_ptrhash);

    /* Now get the length of the shortest path(s) from f to 1. */
    (void) getShortest(f, weight, NULL, visited);

    complement = Cudd_IsComplement(f);

    F = Cudd_Regular(f);

    if (!st_lookup(visited, F, &my_pair)) return(CUDD_OUT_OF_MEM);
    
    if (complement) {
        cost = my_pair->neg;
    } else {
        cost = my_pair->pos;
    }

    st_foreach(visited, freePathPair, NULL);
    st_free_table(visited);

    return(cost);

} /* end of Cudd_ShortestLength */


DdNode *
Cudd_Decreasing(
  DdManager * dd,
  DdNode * f,
  int  i)
{
    unsigned int topf, level;
    DdNode *F, *fv, *fvn, *res;
    DD_CTFP cacheOp;

    statLine(dd);
#ifdef DD_DEBUG
    assert(0 <= i && i < dd->size);
#endif

    F = Cudd_Regular(f);
    topf = cuddI(dd,F->index);

    /* Check terminal case. If topf > i, f does not depend on var.
    ** Therefore, f is unate in i.
    */
    level = (unsigned) dd->perm[i];
    if (topf > level) {
        return(DD_ONE(dd));
    }

    /* From now on, f is not constant. */

    /* Check cache. */
    cacheOp = (DD_CTFP) Cudd_Decreasing;
    res = cuddCacheLookup2(dd,cacheOp,f,dd->vars[i]);
    if (res != NULL) {
        return(res);
    }

    /* Compute cofactors. */
    fv = cuddT(F); fvn = cuddE(F);
    if (F != f) {
        fv = Cudd_Not(fv);
        fvn = Cudd_Not(fvn);
    }

    if (topf == (unsigned) level) {
        /* Special case: if fv is regular, fv(1,...,1) = 1;
        ** If in addition fvn is complemented, fvn(1,...,1) = 0.
        ** But then f(1,1,...,1) > f(0,1,...,1). Hence f is not
        ** monotonic decreasing in i.
        */
        if (!Cudd_IsComplement(fv) && Cudd_IsComplement(fvn)) {
            return(Cudd_Not(DD_ONE(dd)));
        }
        res = Cudd_bddLeq(dd,fv,fvn) ? DD_ONE(dd) : Cudd_Not(DD_ONE(dd));
    } else {
        res = Cudd_Decreasing(dd,fv,i);
        if (res == DD_ONE(dd)) {
            res = Cudd_Decreasing(dd,fvn,i);
        }
    }

    cuddCacheInsert2(dd,cacheOp,f,dd->vars[i],res);
    return(res);

} /* end of Cudd_Decreasing */


DdNode *
Cudd_Increasing(
  DdManager * dd,
  DdNode * f,
  int  i)
{
    return(Cudd_Decreasing(dd,Cudd_Not(f),i));

} /* end of Cudd_Increasing */


int
Cudd_EquivDC(
  DdManager * dd,
  DdNode * F,
  DdNode * G,
  DdNode * D)
{
    DdNode *tmp, *One, *Gr, *Dr;
    DdNode *Fv, *Fvn, *Gv, *Gvn, *Dv, *Dvn;
    int res;
    unsigned int flevel, glevel, dlevel, top;

    One = DD_ONE(dd);

    statLine(dd);
    /* Check terminal cases. */
    if (D == One || F == G) return(1);
    if (D == Cudd_Not(One) || D == DD_ZERO(dd) || F == Cudd_Not(G)) return(0);

    /* From now on, D is non-constant. */

    /* Normalize call to increase cache efficiency. */
    if (F > G) {
        tmp = F;
        F = G;
        G = tmp;
    }
    if (Cudd_IsComplement(F)) {
        F = Cudd_Not(F);
        G = Cudd_Not(G);
    }

    /* From now on, F is regular. */

    /* Check cache. */
    tmp = cuddCacheLookup(dd,DD_EQUIV_DC_TAG,F,G,D);
    if (tmp != NULL) return(tmp == One);

    /* Find splitting variable. */
    flevel = cuddI(dd,F->index);
    Gr = Cudd_Regular(G);
    glevel = cuddI(dd,Gr->index);
    top = ddMin(flevel,glevel);
    Dr = Cudd_Regular(D);
    dlevel = dd->perm[Dr->index];
    top = ddMin(top,dlevel);

    /* Compute cofactors. */
    if (top == flevel) {
        Fv = cuddT(F);
        Fvn = cuddE(F);
    } else {
        Fv = Fvn = F;
    }
    if (top == glevel) {
        Gv = cuddT(Gr);
        Gvn = cuddE(Gr);
        if (G != Gr) {
            Gv = Cudd_Not(Gv);
            Gvn = Cudd_Not(Gvn);
        }
    } else {
        Gv = Gvn = G;
    }
    if (top == dlevel) {
        Dv = cuddT(Dr);
        Dvn = cuddE(Dr);
        if (D != Dr) {
            Dv = Cudd_Not(Dv);
            Dvn = Cudd_Not(Dvn);
        }
    } else {
        Dv = Dvn = D;
    }

    /* Solve recursively. */
    res = Cudd_EquivDC(dd,Fv,Gv,Dv);
    if (res != 0) {
        res = Cudd_EquivDC(dd,Fvn,Gvn,Dvn);
    }
    cuddCacheInsert(dd,DD_EQUIV_DC_TAG,F,G,D,(res) ? One : Cudd_Not(One));

    return(res);

} /* end of Cudd_EquivDC */


int
Cudd_bddLeqUnless(
  DdManager *dd,
  DdNode *f,
  DdNode *g,
  DdNode *D)
{
    DdNode *tmp, *One, *F, *G;
    DdNode *Ft, *Fe, *Gt, *Ge, *Dt, *De;
    int res;
    unsigned int flevel, glevel, dlevel, top;

    statLine(dd);

    One = DD_ONE(dd);

    /* Check terminal cases. */
    if (f == g || g == One || f == Cudd_Not(One) || D == One ||
        D == f || D == Cudd_Not(g)) return(1);
    /* Check for two-operand cases. */
    if (D == Cudd_Not(One) || D == g || D == Cudd_Not(f))
        return(Cudd_bddLeq(dd,f,g));
    if (g == Cudd_Not(One) || g == Cudd_Not(f)) return(Cudd_bddLeq(dd,f,D));
    if (f == One) return(Cudd_bddLeq(dd,Cudd_Not(g),D));

    /* From now on, f, g, and D are non-constant, distinct, and
    ** non-complementary. */

    /* Normalize call to increase cache efficiency.  We rely on the
    ** fact that f <= g unless D is equivalent to not(g) <= not(f)
    ** unless D and to f <= D unless g.  We make sure that D is
    ** regular, and that at most one of f and g is complemented.  We also
    ** ensure that when two operands can be swapped, the one with the
    ** lowest address comes first. */

    if (Cudd_IsComplement(D)) {
        if (Cudd_IsComplement(g)) {
            /* Special case: if f is regular and g is complemented,
            ** f(1,...,1) = 1 > 0 = g(1,...,1).  If D(1,...,1) = 0, return 0.
            */
            if (!Cudd_IsComplement(f)) return(0);
            /* !g <= D unless !f  or  !D <= g unless !f */
            tmp = D;
            D = Cudd_Not(f);
            if (g < tmp) {
                f = Cudd_Not(g);
                g = tmp;
            } else {
                f = Cudd_Not(tmp);
            }
        } else {
            if (Cudd_IsComplement(f)) {
                /* !D <= !f unless g  or  !D <= g unless !f */
                tmp = f;
                f = Cudd_Not(D);
                if (tmp < g) {
                    D = g;
                    g = Cudd_Not(tmp);
                } else {
                    D = Cudd_Not(tmp);
                }
            } else {
                /* f <= D unless g  or  !D <= !f unless g */
                tmp = D;
                D = g;
                if (tmp < f) {
                    g = Cudd_Not(f);
                    f = Cudd_Not(tmp);
                } else {
                    g = tmp;
                }
            }
        }
    } else {
        if (Cudd_IsComplement(g)) {
            if (Cudd_IsComplement(f)) {
                /* !g <= !f unless D  or  !g <= D unless !f */
                tmp = f;
                f = Cudd_Not(g);
                if (D < tmp) {
                    g = D;
                    D = Cudd_Not(tmp);
                } else {
                    g = Cudd_Not(tmp);
                }
            } else {
                /* f <= g unless D  or  !g <= !f unless D */
                if (g < f) {
                    tmp = g;
                    g = Cudd_Not(f);
                    f = Cudd_Not(tmp);
                }
            }
        } else {
            /* f <= g unless D  or  f <= D unless g */
            if (D < g) {
                tmp = D;
                D = g;
                g = tmp;
            }
        }
    }

    /* From now on, D is regular. */

    /* Check cache. */
    tmp = cuddCacheLookup(dd,DD_BDD_LEQ_UNLESS_TAG,f,g,D);
    if (tmp != NULL) return(tmp == One);

    /* Find splitting variable. */
    F = Cudd_Regular(f);
    flevel = dd->perm[F->index];
    G = Cudd_Regular(g);
    glevel = dd->perm[G->index];
    top = ddMin(flevel,glevel);
    dlevel = dd->perm[D->index];
    top = ddMin(top,dlevel);

    /* Compute cofactors. */
    if (top == flevel) {
        Ft = cuddT(F);
        Fe = cuddE(F);
        if (F != f) {
            Ft = Cudd_Not(Ft);
            Fe = Cudd_Not(Fe);
        }
    } else {
        Ft = Fe = f;
    }
    if (top == glevel) {
        Gt = cuddT(G);
        Ge = cuddE(G);
        if (G != g) {
            Gt = Cudd_Not(Gt);
            Ge = Cudd_Not(Ge);
        }
    } else {
        Gt = Ge = g;
    }
    if (top == dlevel) {
        Dt = cuddT(D);
        De = cuddE(D);
    } else {
        Dt = De = D;
    }

    /* Solve recursively. */
    res = Cudd_bddLeqUnless(dd,Ft,Gt,Dt);
    if (res != 0) {
        res = Cudd_bddLeqUnless(dd,Fe,Ge,De);
    }
    cuddCacheInsert(dd,DD_BDD_LEQ_UNLESS_TAG,f,g,D,Cudd_NotCond(One,!res));

    return(res);

} /* end of Cudd_bddLeqUnless */


int
Cudd_EqualSupNorm(
  DdManager * dd /* manager */,
  DdNode * f /* first ADD */,
  DdNode * g /* second ADD */,
  CUDD_VALUE_TYPE  tolerance /* maximum allowed difference */,
  int  pr /* verbosity level */)
{
    DdNode *fv, *fvn, *gv, *gvn, *r;
    unsigned int topf, topg;

    statLine(dd);
    /* Check terminal cases. */
    if (f == g) return(1);
    if (Cudd_IsConstant(f) && Cudd_IsConstant(g)) {
        if (ddEqualVal(cuddV(f),cuddV(g),tolerance)) {
            return(1);
        } else {
            if (pr>0) {
                (void) fprintf(dd->out,"Offending nodes:\n");
                (void) fprintf(dd->out,
                               "f: address = %p\t value = %40.30f\n",
                               (void *) f, cuddV(f));
                (void) fprintf(dd->out,
                               "g: address = %p\t value = %40.30f\n",
                               (void *) g, cuddV(g));
            }
            return(0);
        }
    }

    /* We only insert the result in the cache if the comparison is
    ** successful. Therefore, if we hit we return 1. */
    r = cuddCacheLookup2(dd,(DD_CTFP)Cudd_EqualSupNorm,f,g);
    if (r != NULL) {
        return(1);
    }

    /* Compute the cofactors and solve the recursive subproblems. */
    topf = cuddI(dd,f->index);
    topg = cuddI(dd,g->index);

    if (topf <= topg) {fv = cuddT(f); fvn = cuddE(f);} else {fv = fvn = f;}
    if (topg <= topf) {gv = cuddT(g); gvn = cuddE(g);} else {gv = gvn = g;}

    if (!Cudd_EqualSupNorm(dd,fv,gv,tolerance,pr)) return(0);
    if (!Cudd_EqualSupNorm(dd,fvn,gvn,tolerance,pr)) return(0);

    cuddCacheInsert2(dd,(DD_CTFP)Cudd_EqualSupNorm,f,g,DD_ONE(dd));

    return(1);

} /* end of Cudd_EqualSupNorm */


DdNode *
Cudd_bddMakePrime(
  DdManager *dd /* manager */,
  DdNode *cube /* cube to be expanded */,
  DdNode *f /* function of which the cube is to be made a prime */)
{
    DdNode *res;

    if (!Cudd_bddLeq(dd,cube,f)) return(NULL);

    do {
        dd->reordered = 0;
        res = cuddBddMakePrime(dd,cube,f);
    } while (dd->reordered == 1);
    return(res);

} /* end of Cudd_bddMakePrime */


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


DdNode *
cuddBddMakePrime(
  DdManager *dd /* manager */,
  DdNode *cube /* cube to be expanded */,
  DdNode *f /* function of which the cube is to be made a prime */)
{
    DdNode *scan;
    DdNode *t, *e;
    DdNode *res = cube;
    DdNode *zero = Cudd_Not(DD_ONE(dd));

    Cudd_Ref(res);
    scan = cube;
    while (!Cudd_IsConstant(scan)) {
        DdNode *reg = Cudd_Regular(scan);
        DdNode *var = dd->vars[reg->index];
        DdNode *expanded = Cudd_bddExistAbstract(dd,res,var);
        if (expanded == NULL) {
            return(NULL);
        }
        Cudd_Ref(expanded);
        if (Cudd_bddLeq(dd,expanded,f)) {
            Cudd_RecursiveDeref(dd,res);
            res = expanded;
        } else {
            Cudd_RecursiveDeref(dd,expanded);
        }
        cuddGetBranches(scan,&t,&e);
        if (t == zero) {
            scan = e;
        } else if (e == zero) {
            scan = t;
        } else {
            Cudd_RecursiveDeref(dd,res);
            return(NULL);       /* cube is not a cube */
        }
    }

    if (scan == DD_ONE(dd)) {
        Cudd_Deref(res);
        return(res);
    } else {
        Cudd_RecursiveDeref(dd,res);
        return(NULL);
    }

} /* end of cuddBddMakePrime */


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


static enum st_retval
freePathPair(
  char * key,
  char * value,
  char * arg)
{
    cuddPathPair *pair;

    pair = (cuddPathPair *) value;
        FREE(pair);
    return(ST_CONTINUE);

} /* end of freePathPair */


static cuddPathPair
getShortest(
  DdNode * root,
  int * cost,
  int * support,
  st_table * visited)
{
    cuddPathPair *my_pair, res_pair, pair_T, pair_E;
    DdNode      *my_root, *T, *E;
    int         weight;

    my_root = Cudd_Regular(root);

    if (st_lookup(visited, my_root, &my_pair)) {
        if (Cudd_IsComplement(root)) {
            res_pair.pos = my_pair->neg;
            res_pair.neg = my_pair->pos;
        } else {
            res_pair.pos = my_pair->pos;
            res_pair.neg = my_pair->neg;
        }
        return(res_pair);
    }

    /* In the case of a BDD the following test is equivalent to
    ** testing whether the BDD is the constant 1. This formulation,
    ** however, works for ADDs as well, by assuming the usual
    ** dichotomy of 0 and != 0.
    */
    if (cuddIsConstant(my_root)) {
        if (my_root != zero) {
            res_pair.pos = 0;
            res_pair.neg = DD_BIGGY;
        } else {
            res_pair.pos = DD_BIGGY;
            res_pair.neg = 0;
        }
    } else {
        T = cuddT(my_root);
        E = cuddE(my_root);

        pair_T = getShortest(T, cost, support, visited);
        pair_E = getShortest(E, cost, support, visited);
        weight = WEIGHT(cost, my_root->index);
        res_pair.pos = ddMin(pair_T.pos+weight, pair_E.pos);
        res_pair.neg = ddMin(pair_T.neg+weight, pair_E.neg);

        /* Update support. */
        if (support != NULL) {
            support[my_root->index] = 1;
        }
    }

    my_pair = ALLOC(cuddPathPair, 1);
    if (my_pair == NULL) {
        if (Cudd_IsComplement(root)) {
            int tmp = res_pair.pos;
            res_pair.pos = res_pair.neg;
            res_pair.neg = tmp;
        }
        return(res_pair);
    }
    my_pair->pos = res_pair.pos;
    my_pair->neg = res_pair.neg;

    st_insert(visited, (char *)my_root, (char *)my_pair);
    if (Cudd_IsComplement(root)) {
        res_pair.pos = my_pair->neg;
        res_pair.neg = my_pair->pos;
    } else {
        res_pair.pos = my_pair->pos;
        res_pair.neg = my_pair->neg;
    }
    return(res_pair);

} /* end of getShortest */


static DdNode *
getPath(
  DdManager * manager,
  st_table * visited,
  DdNode * f,
  int * weight,
  int  cost)
{
    DdNode      *sol, *tmp;
    DdNode      *my_dd, *T, *E;
    cuddPathPair *T_pair, *E_pair;
    int         Tcost, Ecost;
    int         complement;

    my_dd = Cudd_Regular(f);
    complement = Cudd_IsComplement(f);

    sol = one;
    cuddRef(sol);

    while (!cuddIsConstant(my_dd)) {
        Tcost = cost - WEIGHT(weight, my_dd->index);
        Ecost = cost;

        T = cuddT(my_dd);
        E = cuddE(my_dd);

        if (complement) {T = Cudd_Not(T); E = Cudd_Not(E);}

        st_lookup(visited, Cudd_Regular(T), &T_pair);
        if ((Cudd_IsComplement(T) && T_pair->neg == Tcost) ||
        (!Cudd_IsComplement(T) && T_pair->pos == Tcost)) {
            tmp = cuddBddAndRecur(manager,manager->vars[my_dd->index],sol);
            if (tmp == NULL) {
                Cudd_RecursiveDeref(manager,sol);
                return(NULL);
            }
            cuddRef(tmp);
            Cudd_RecursiveDeref(manager,sol);
            sol = tmp;

            complement =  Cudd_IsComplement(T);
            my_dd = Cudd_Regular(T);
            cost = Tcost;
            continue;
        }
        st_lookup(visited, Cudd_Regular(E), &E_pair);
        if ((Cudd_IsComplement(E) && E_pair->neg == Ecost) ||
        (!Cudd_IsComplement(E) && E_pair->pos == Ecost)) {
            tmp = cuddBddAndRecur(manager,Cudd_Not(manager->vars[my_dd->index]),sol);
            if (tmp == NULL) {
                Cudd_RecursiveDeref(manager,sol);
                return(NULL);
            }
            cuddRef(tmp);
            Cudd_RecursiveDeref(manager,sol);
            sol = tmp;
            complement = Cudd_IsComplement(E);
            my_dd = Cudd_Regular(E);
            cost = Ecost;
            continue;
        }
        (void) fprintf(manager->err,"We shouldn't be here!!\n");
        manager->errorCode = CUDD_INTERNAL_ERROR;
        return(NULL);
    }

    cuddDeref(sol);
    return(sol);

} /* end of getPath */


static cuddPathPair
getLargest(
  DdNode * root,
  st_table * visited)
{
    cuddPathPair *my_pair, res_pair, pair_T, pair_E;
    DdNode      *my_root, *T, *E;

    my_root = Cudd_Regular(root);

    if (st_lookup(visited, my_root, &my_pair)) {
        if (Cudd_IsComplement(root)) {
            res_pair.pos = my_pair->neg;
            res_pair.neg = my_pair->pos;
        } else {
            res_pair.pos = my_pair->pos;
            res_pair.neg = my_pair->neg;
        }
        return(res_pair);
    }

    /* In the case of a BDD the following test is equivalent to
    ** testing whether the BDD is the constant 1. This formulation,
    ** however, works for ADDs as well, by assuming the usual
    ** dichotomy of 0 and != 0.
    */
    if (cuddIsConstant(my_root)) {
        if (my_root != zero) {
            res_pair.pos = 0;
            res_pair.neg = DD_BIGGY;
        } else {
            res_pair.pos = DD_BIGGY;
            res_pair.neg = 0;
        }
    } else {
        T = cuddT(my_root);
        E = cuddE(my_root);

        pair_T = getLargest(T, visited);
        pair_E = getLargest(E, visited);
        res_pair.pos = ddMin(pair_T.pos, pair_E.pos) + 1;
        res_pair.neg = ddMin(pair_T.neg, pair_E.neg) + 1;
    }

    my_pair = ALLOC(cuddPathPair, 1);
    if (my_pair == NULL) {      /* simply do not cache this result */
        if (Cudd_IsComplement(root)) {
            int tmp = res_pair.pos;
            res_pair.pos = res_pair.neg;
            res_pair.neg = tmp;
        }
        return(res_pair);
    }
    my_pair->pos = res_pair.pos;
    my_pair->neg = res_pair.neg;

    /* Caching may fail without affecting correctness. */
    st_insert(visited, (char *)my_root, (char *)my_pair);
    if (Cudd_IsComplement(root)) {
        res_pair.pos = my_pair->neg;
        res_pair.neg = my_pair->pos;
    } else {
        res_pair.pos = my_pair->pos;
        res_pair.neg = my_pair->neg;
    }
    return(res_pair);

} /* end of getLargest */


static DdNode *
getCube(
  DdManager * manager,
  st_table * visited,
  DdNode * f,
  int  cost)
{
    DdNode      *sol, *tmp;
    DdNode      *my_dd, *T, *E;
    cuddPathPair *T_pair, *E_pair;
    int         Tcost, Ecost;
    int         complement;

    my_dd = Cudd_Regular(f);
    complement = Cudd_IsComplement(f);

    sol = one;
    cuddRef(sol);

    while (!cuddIsConstant(my_dd)) {
        Tcost = cost - 1;
        Ecost = cost - 1;

        T = cuddT(my_dd);
        E = cuddE(my_dd);

        if (complement) {T = Cudd_Not(T); E = Cudd_Not(E);}

        if (!st_lookup(visited, Cudd_Regular(T), &T_pair)) return(NULL);
        if ((Cudd_IsComplement(T) && T_pair->neg == Tcost) ||
        (!Cudd_IsComplement(T) && T_pair->pos == Tcost)) {
            tmp = cuddBddAndRecur(manager,manager->vars[my_dd->index],sol);
            if (tmp == NULL) {
                Cudd_RecursiveDeref(manager,sol);
                return(NULL);
            }
            cuddRef(tmp);
            Cudd_RecursiveDeref(manager,sol);
            sol = tmp;

            complement =  Cudd_IsComplement(T);
            my_dd = Cudd_Regular(T);
            cost = Tcost;
            continue;
        }
        if (!st_lookup(visited, Cudd_Regular(E), &E_pair)) return(NULL);
        if ((Cudd_IsComplement(E) && E_pair->neg == Ecost) ||
        (!Cudd_IsComplement(E) && E_pair->pos == Ecost)) {
            tmp = cuddBddAndRecur(manager,Cudd_Not(manager->vars[my_dd->index]),sol);
            if (tmp == NULL) {
                Cudd_RecursiveDeref(manager,sol);
                return(NULL);
            }
            cuddRef(tmp);
            Cudd_RecursiveDeref(manager,sol);
            sol = tmp;
            complement = Cudd_IsComplement(E);
            my_dd = Cudd_Regular(E);
            cost = Ecost;
            continue;
        }
        (void) fprintf(manager->err,"We shouldn't be here!\n");
        manager->errorCode = CUDD_INTERNAL_ERROR;
        return(NULL);
    }

    cuddDeref(sol);
    return(sol);

} /* end of getCube */

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