/**CFile****************************************************************

  FileName    [abcDfs.c]

  SystemName  [ABC: Logic synthesis and verification system.]

  PackageName [Network and node package.]

  Synopsis    [Procedures that use depth-first search.]

  Author      [Alan Mishchenko]
  
  Affiliation [UC Berkeley]

  Date        [Ver. 1.0. Started - June 20, 2005.]

  Revision    [$Id: abcDfs.c,v 1.00 2005/06/20 00:00:00 alanmi Exp $]

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

#include "abc.h"

////////////////////////////////////////////////////////////////////////
///                        DECLARATIONS                              ///
////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////
///                     FUNCTION DEFINITIONS                         ///
////////////////////////////////////////////////////////////////////////

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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfs_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanin;
    int i;
    assert( !Abc_ObjIsNet(pNode) );
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // skip the CI
    if ( Abc_ObjIsCi(pNode) || (Abc_NtkIsStrash(pNode->pNtk) && Abc_AigNodeIsConst(pNode)) )
        return;
    assert( Abc_ObjIsNode( pNode ) || Abc_ObjIsBox( pNode ) );
    // visit the transitive fanin of the node
    Abc_ObjForEachFanin( pNode, pFanin, i )
    {
//        pFanin = Abc_ObjFanin( pNode, Abc_ObjFaninNum(pNode)-1-i );
        Abc_NtkDfs_rec( Abc_ObjFanin0Ntk(pFanin), vNodes );
    }
    // add the node after the fanins have been added
    Vec_PtrPush( vNodes, pNode );
}

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

  Synopsis    [Returns the DFS ordered array of logic nodes.]

  Description [Collects only the internal nodes, leaving out CIs and CO.
  However it marks with the current TravId both CIs and COs.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfs( Abc_Ntk_t * pNtk, int fCollectAll )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj;
    int i;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    Abc_NtkForEachCo( pNtk, pObj, i )
    {
        Abc_NodeSetTravIdCurrent( pObj );
        Abc_NtkDfs_rec( Abc_ObjFanin0Ntk(Abc_ObjFanin0(pObj)), vNodes );
    }
    // collect dangling nodes if asked to
    if ( fCollectAll )
    {
        Abc_NtkForEachNode( pNtk, pObj, i )
            if ( !Abc_NodeIsTravIdCurrent(pObj) )
                Abc_NtkDfs_rec( pObj, vNodes );
    }
    return vNodes;
}

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

  Synopsis    [Returns the DFS ordered array of logic nodes.]

  Description [Collects only the internal nodes, leaving out PIs, POs and latches.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsNodes( Abc_Ntk_t * pNtk, Abc_Obj_t ** ppNodes, int nNodes )
{
    Vec_Ptr_t * vNodes;
    int i;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    // go through the PO nodes and call for each of them
    for ( i = 0; i < nNodes; i++ )
    {
        if ( Abc_NtkIsStrash(pNtk) && Abc_AigNodeIsConst(ppNodes[i]) )
            continue;
        if ( Abc_ObjIsCo(ppNodes[i]) )
        {
            Abc_NodeSetTravIdCurrent(ppNodes[i]);
            Abc_NtkDfs_rec( Abc_ObjFanin0Ntk(Abc_ObjFanin0(ppNodes[i])), vNodes );
        }
        else if ( Abc_ObjIsNode(ppNodes[i]) )
            Abc_NtkDfs_rec( ppNodes[i], vNodes );
    }
    return vNodes;
}


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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfsReverse_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanout;
    int i;
    assert( !Abc_ObjIsNet(pNode) );
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // skip the CI
    if ( Abc_ObjIsCo(pNode) )
        return;
    assert( Abc_ObjIsNode( pNode ) );
    // visit the transitive fanin of the node
    pNode = Abc_ObjFanout0Ntk(pNode);
    Abc_ObjForEachFanout( pNode, pFanout, i )
        Abc_NtkDfsReverse_rec( pFanout, vNodes );
    // add the node after the fanins have been added
    Vec_PtrPush( vNodes, pNode );
}

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

  Synopsis    [Returns the reverse DFS ordered array of logic nodes.]

  Description [Collects only the internal nodes, leaving out CIs/COs.
  However it marks both CIs and COs with the current TravId.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsReverse( Abc_Ntk_t * pNtk )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj, * pFanout;
    int i, k;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    Abc_NtkForEachCi( pNtk, pObj, i )
    {
        Abc_NodeSetTravIdCurrent( pObj );
        pObj = Abc_ObjFanout0Ntk(pObj);
        Abc_ObjForEachFanout( pObj, pFanout, k )
            Abc_NtkDfsReverse_rec( pFanout, vNodes );
    }
    // add constant nodes in the end
    if ( !Abc_NtkIsStrash(pNtk) )
        Abc_NtkForEachNode( pNtk, pObj, i )
            if ( Abc_NodeIsConst(pObj) )
                Vec_PtrPush( vNodes, pObj );
    return vNodes;
}

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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfsReverseNodes_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanout;
    int i;
    assert( !Abc_ObjIsNet(pNode) );
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // skip the CI
    if ( Abc_ObjIsCo(pNode) )
        return;
    assert( Abc_ObjIsNode( pNode ) );
    // visit the transitive fanin of the node
    pNode = Abc_ObjFanout0Ntk(pNode);
    Abc_ObjForEachFanout( pNode, pFanout, i )
        Abc_NtkDfsReverseNodes_rec( pFanout, vNodes );
    // add the node after the fanins have been added
//    Vec_PtrPush( vNodes, pNode );
    Vec_PtrFillExtra( vNodes, pNode->Level + 1, NULL );
    pNode->pCopy = Vec_PtrEntry( vNodes, pNode->Level );
    Vec_PtrWriteEntry( vNodes, pNode->Level, pNode );
}

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

  Synopsis    [Returns the levelized array of TFO nodes.]

  Description [Collects the levelized array of internal nodes, leaving out CIs/COs.
  However it marks both CIs and COs with the current TravId.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsReverseNodes( Abc_Ntk_t * pNtk, Abc_Obj_t ** ppNodes, int nNodes )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj, * pFanout;
    int i, k;
    assert( Abc_NtkIsStrash(pNtk) );
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrStart( Abc_AigLevel(pNtk) + 1 );
    for ( i = 0; i < nNodes; i++ )
    {
        pObj = ppNodes[i];
        assert( Abc_ObjIsCi(pObj) );
        Abc_NodeSetTravIdCurrent( pObj );
        pObj = Abc_ObjFanout0Ntk(pObj);
        Abc_ObjForEachFanout( pObj, pFanout, k )
            Abc_NtkDfsReverseNodes_rec( pFanout, vNodes );
    }
    return vNodes;
}

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

  Synopsis    [Returns the levelized array of TFO nodes.]

  Description [Collects the levelized array of internal nodes, leaving out CIs/COs.
  However it marks both CIs and COs with the current TravId.
  Collects only the nodes whose support does not exceed the set of given CI nodes.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsReverseNodesContained( Abc_Ntk_t * pNtk, Abc_Obj_t ** ppNodes, int nNodes )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj, * pFanout, * pFanin;
    int i, k, m, nLevels;
    // set the levels
    nLevels = Abc_NtkLevel( pNtk );
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrStart( nLevels + 2 );
    for ( i = 0; i < nNodes; i++ )
    {
        pObj = ppNodes[i];
        assert( Abc_ObjIsCi(pObj) );
        Abc_NodeSetTravIdCurrent( pObj );
        // add to the array
        assert( pObj->Level == 0 );
        pObj->pCopy = Vec_PtrEntry( vNodes, pObj->Level );
        Vec_PtrWriteEntry( vNodes, pObj->Level, pObj );
    }
    // iterate through the levels
    for ( i = 0; i <= nLevels; i++ )
    {
        // iterate through the nodes on each level
        for ( pObj = Vec_PtrEntry(vNodes, i); pObj; pObj = pObj->pCopy )
        {
            // iterate through the fanouts of each node
            Abc_ObjForEachFanout( pObj, pFanout, k )
            {
                // skip visited nodes
                if ( Abc_NodeIsTravIdCurrent(pFanout) )
                    continue;
                // visit the fanins of this fanout
                Abc_ObjForEachFanin( pFanout, pFanin, m )
                {
                    if ( !Abc_NodeIsTravIdCurrent(pFanin) )
                        break;
                }
                if ( m < Abc_ObjFaninNum(pFanout) )
                    continue;
                // all fanins are already collected

                // mark the node as visited
                Abc_NodeSetTravIdCurrent( pFanout );
                // handle the COs
                if ( Abc_ObjIsCo(pFanout) )
                    pFanout->Level = nLevels + 1;
                // add to the array
                pFanout->pCopy = Vec_PtrEntry( vNodes, pFanout->Level );
                Vec_PtrWriteEntry( vNodes, pFanout->Level, pFanout );
                // handle the COs
                if ( Abc_ObjIsCo(pFanout) )
                    pFanout->Level = 0;
            }
        }
    }
    return vNodes;
}


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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfsSeq_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanin;
    int i;
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // visit the transitive fanin of the node
    Abc_ObjForEachFanin( pNode, pFanin, i )
        Abc_NtkDfsSeq_rec( pFanin, vNodes );
    // add the node after the fanins have been added
    Vec_PtrPush( vNodes, pNode );
}

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

  Synopsis    [Returns the array of nodes and latches reachable from POs.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsSeq( Abc_Ntk_t * pNtk )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj;
    int i;
    assert( !Abc_NtkIsNetlist(pNtk) );
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    Abc_NtkForEachPo( pNtk, pObj, i )
        Abc_NtkDfsSeq_rec( pObj, vNodes );
    // mark the PIs
    Abc_NtkForEachPi( pNtk, pObj, i )
        Abc_NtkDfsSeq_rec( pObj, vNodes );
    return vNodes;
}


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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfsSeqReverse_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanout;
    int i;
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // visit the transitive fanin of the node
    Abc_ObjForEachFanout( pNode, pFanout, i )
        Abc_NtkDfsSeqReverse_rec( pFanout, vNodes );
    // add the node after the fanins have been added
    Vec_PtrPush( vNodes, pNode );
}

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

  Synopsis    [Returns the array of nodes and latches reachable from POs.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsSeqReverse( Abc_Ntk_t * pNtk )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj;
    int i;
    assert( !Abc_NtkIsNetlist(pNtk) );
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    Abc_NtkForEachPi( pNtk, pObj, i )
        Abc_NtkDfsSeqReverse_rec( pObj, vNodes );
    // mark the logic feeding into POs
    Abc_NtkForEachPo( pNtk, pObj, i )
        Abc_NtkDfsSeq_rec( pObj, vNodes );
    return vNodes;
}


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

  Synopsis    [Iterative version of the DFS procedure.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfs_iter( Vec_Ptr_t * vStack, Abc_Obj_t * pRoot, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pNode, * pFanin;
    int iFanin;
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pRoot ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pRoot );
    // skip the CI
    if ( Abc_ObjIsCi(pRoot) || (Abc_NtkIsStrash(pRoot->pNtk) && Abc_AigNodeIsConst(pRoot)) )
        return;
    // add the CI
    Vec_PtrClear( vStack );
    Vec_PtrPush( vStack, pRoot );
    Vec_PtrPush( vStack, (void *)0 );
    while ( Vec_PtrSize(vStack) > 0 )
    {
        // get the node and its fanin
        iFanin = (int)Vec_PtrPop(vStack);
        pNode  = Vec_PtrPop(vStack);
        assert( !Abc_ObjIsNet(pNode) );
        // add it to the array of nodes if we finished
        if ( iFanin == Abc_ObjFaninNum(pNode) )
        {
            Vec_PtrPush( vNodes, pNode );
            continue;
        }
        // explore the next fanin
        Vec_PtrPush( vStack, pNode );
        Vec_PtrPush( vStack, (void *)(iFanin+1) );
        // get the fanin
        pFanin = Abc_ObjFanin0Ntk( Abc_ObjFanin(pNode,iFanin) );
        // if this node is already visited, skip
        if ( Abc_NodeIsTravIdCurrent( pFanin ) )
            continue;
        // mark the node as visited
        Abc_NodeSetTravIdCurrent( pFanin );
        // skip the CI
        if ( Abc_ObjIsCi(pFanin) || (Abc_NtkIsStrash(pFanin->pNtk) && Abc_AigNodeIsConst(pFanin)) )
            continue;
        Vec_PtrPush( vStack, pFanin );
        Vec_PtrPush( vStack, (void *)0 );   
    }
}

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

  Synopsis    [Returns the DFS ordered array of logic nodes.]

  Description [Collects only the internal nodes, leaving CIs and CO.
  However it marks with the current TravId both CIs and COs.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsIter( Abc_Ntk_t * pNtk, int fCollectAll )
{
    Vec_Ptr_t * vNodes, * vStack;
    Abc_Obj_t * pObj;
    int i;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 1000 );
    vStack = Vec_PtrAlloc( 1000 );
    Abc_NtkForEachCo( pNtk, pObj, i )
    {
        Abc_NodeSetTravIdCurrent( pObj );
        Abc_NtkDfs_iter( vStack, Abc_ObjFanin0Ntk(Abc_ObjFanin0(pObj)), vNodes );
    }
    // collect dangling nodes if asked to
    if ( fCollectAll )
    {
        Abc_NtkForEachNode( pNtk, pObj, i )
            if ( !Abc_NodeIsTravIdCurrent(pObj) )
                Abc_NtkDfs_iter( vStack, pObj, vNodes );
    }
    Vec_PtrFree( vStack );
    return vNodes;
}


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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkDfsHie_rec( Abc_Obj_t * pObj, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanin;
    int i;
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pObj ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pObj );
    // visit the transitive fanin of the node
    Abc_ObjForEachFanin( pObj, pFanin, i )
        Abc_NtkDfsHie_rec( pFanin, vNodes );
    // add the node after the fanins have been added
    Vec_PtrPush( vNodes, pObj );
}

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

  Synopsis    [Returns the DFS ordered array of all objects.]

  Description [This procedure collects everything from POs to PIs.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkDfsHie( Abc_Ntk_t * pNtk, int fCollectAll )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pObj;
    int i;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    Abc_NtkForEachPo( pNtk, pObj, i )
        Abc_NtkDfsHie_rec( pObj, vNodes );
    // collect dangling nodes if asked to
    if ( fCollectAll )
    {
        Abc_NtkForEachObj( pNtk, pObj, i )
            if ( !Abc_NodeIsTravIdCurrent(pObj) )
                Abc_NtkDfs_rec( pObj, vNodes );
    }
    return vNodes;
}


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

  Synopsis    [Returns 1 if the ordering of nodes is DFS.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
bool Abc_NtkIsDfsOrdered( Abc_Ntk_t * pNtk )
{
    Abc_Obj_t * pNode, * pFanin;
    int i, k;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // mark the CIs
    Abc_NtkForEachCi( pNtk, pNode, i )
        Abc_NodeSetTravIdCurrent( pNode );
    // go through the nodes
    Abc_NtkForEachNode( pNtk, pNode, i )
    {
        // check the fanins of the node
        Abc_ObjForEachFanin( pNode, pFanin, k )
            if ( !Abc_NodeIsTravIdCurrent(pFanin) )
                return 0;
        // check the choices of the node
        if ( Abc_NtkIsStrash(pNtk) && Abc_AigNodeIsChoice(pNode) )
            for ( pFanin = pNode->pData; pFanin; pFanin = pFanin->pData )
                if ( !Abc_NodeIsTravIdCurrent(pFanin) )
                    return 0;
        // mark the node as visited
        Abc_NodeSetTravIdCurrent( pNode );
    }
    return 1;
}


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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkNodeSupport_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanin;
    int i;
    assert( !Abc_ObjIsNet(pNode) );
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // collect the CI
    if ( Abc_ObjIsCi(pNode) || (Abc_NtkIsStrash(pNode->pNtk) && Abc_ObjFaninNum(pNode) == 0) )
    {
        Vec_PtrPush( vNodes, pNode );
        return;
    }
    assert( Abc_ObjIsNode( pNode ) );
    // visit the transitive fanin of the node
    Abc_ObjForEachFanin( pNode, pFanin, i )
        Abc_NtkNodeSupport_rec( Abc_ObjFanin0Ntk(pFanin), vNodes );
}

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

  Synopsis    [Returns the set of CI nodes in the support of the given nodes.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkSupport( Abc_Ntk_t * pNtk )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pNode;
    int i;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    // go through the PO nodes and call for each of them
    Abc_NtkForEachCo( pNtk, pNode, i )
        Abc_NtkNodeSupport_rec( Abc_ObjFanin0(pNode), vNodes );
    // add unused CIs
    Abc_NtkForEachCi( pNtk, pNode, i )
        if ( !Abc_NodeIsTravIdCurrent( pNode ) )
            Vec_PtrPush( vNodes, pNode );
    assert( Vec_PtrSize(vNodes) == Abc_NtkCiNum(pNtk) );
    return vNodes;
}

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

  Synopsis    [Returns the set of CI nodes in the support of the given nodes.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_NtkNodeSupport( Abc_Ntk_t * pNtk, Abc_Obj_t ** ppNodes, int nNodes )
{
    Vec_Ptr_t * vNodes;
    int i;
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    // go through the PO nodes and call for each of them
    for ( i = 0; i < nNodes; i++ )
        if ( Abc_ObjIsCo(ppNodes[i]) )
            Abc_NtkNodeSupport_rec( Abc_ObjFanin0(ppNodes[i]), vNodes );
        else
            Abc_NtkNodeSupport_rec( ppNodes[i], vNodes );
    return vNodes;
}

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

  Synopsis    [Computes the sum total of supports of all outputs.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_NtkSupportSum( Abc_Ntk_t * pNtk )
{
    Vec_Ptr_t * vSupp;
    Abc_Obj_t * pObj;
    int i, nTotalSupps = 0;
    Abc_NtkForEachCo( pNtk, pObj, i )
    {
        vSupp = Abc_NtkNodeSupport( pNtk, &pObj, 1 );
        nTotalSupps += Vec_PtrSize( vSupp );
        Vec_PtrFree( vSupp );
    }
    printf( "Total supports = %d.\n", nTotalSupps );
}


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

  Synopsis    [Performs DFS for one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_AigDfs_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
{
    Abc_Obj_t * pFanin;
    int i;
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // skip the PI
    if ( Abc_ObjIsCi(pNode) || Abc_AigNodeIsConst(pNode) )
        return;
    assert( Abc_ObjIsNode( pNode ) );
    // visit the transitive fanin of the node
    Abc_ObjForEachFanin( pNode, pFanin, i )
        Abc_AigDfs_rec( pFanin, vNodes );
    // visit the equivalent nodes
    if ( Abc_AigNodeIsChoice( pNode ) )
        for ( pFanin = pNode->pData; pFanin; pFanin = pFanin->pData )
            Abc_AigDfs_rec( pFanin, vNodes );
    // add the node after the fanins have been added
    Vec_PtrPush( vNodes, pNode );
}

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

  Synopsis    [Returns the DFS ordered array of logic nodes.]

  Description [Collects only the internal nodes, leaving out CIs/COs.
  However it marks both CIs and COs with the current TravId.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_AigDfs( Abc_Ntk_t * pNtk, int fCollectAll, int fCollectCos )
{
    Vec_Ptr_t * vNodes;
    Abc_Obj_t * pNode;
    int i;
    assert( Abc_NtkIsStrash(pNtk) );
    // set the traversal ID
    Abc_NtkIncrementTravId( pNtk );
    // start the array of nodes
    vNodes = Vec_PtrAlloc( 100 );
    // go through the PO nodes and call for each of them
    Abc_NtkForEachCo( pNtk, pNode, i )
    {
        Abc_AigDfs_rec( Abc_ObjFanin0(pNode), vNodes );
        Abc_NodeSetTravIdCurrent( pNode );
        if ( fCollectCos )
            Vec_PtrPush( vNodes, pNode );
    }
    // collect dangling nodes if asked to
    if ( fCollectAll )
    {
        Abc_NtkForEachNode( pNtk, pNode, i )
            if ( !Abc_NodeIsTravIdCurrent(pNode) )
                Abc_AigDfs_rec( pNode, vNodes );
    }
    return vNodes;
}


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

  Synopsis    [Collects nodes in the DFS manner by level.]

  Description [The number of levels should be set!!!]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
void Abc_DfsLevelizedTfo_rec( Abc_Obj_t * pNode, Vec_Vec_t * vLevels )
{
    Abc_Obj_t * pFanout;
    int i;
    // if this node is already visited, skip
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // skip the terminals
    if ( Abc_ObjIsCo(pNode) )
        return;
    assert( Abc_ObjIsNode(pNode) );
    // add the node to the structure
    Vec_VecPush( vLevels, pNode->Level, pNode );
    // visit the TFO
    Abc_ObjForEachFanout( pNode, pFanout, i )
        Abc_DfsLevelizedTfo_rec( pFanout, vLevels );
}

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

  Synopsis    [Collects nodes in the DFS manner by level.]

  Description [The number of levels should be set!!!]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Vec_t * Abc_DfsLevelized( Abc_Obj_t * pNode, bool fTfi )
{
    Vec_Vec_t * vLevels;
    Abc_Obj_t * pFanout;
    int i;
    assert( fTfi == 0 );
    assert( !Abc_NtkIsNetlist(pNode->pNtk) );
    // set the traversal ID
    Abc_NtkIncrementTravId( pNode->pNtk );
    vLevels = Vec_VecAlloc( 100 );
    if ( Abc_ObjIsNode(pNode) )
        Abc_DfsLevelizedTfo_rec( pNode, vLevels );
    else
    {
        assert( Abc_ObjIsCi(pNode) );
        Abc_NodeSetTravIdCurrent( pNode );
        Abc_ObjForEachFanout( pNode, pFanout, i )
            Abc_DfsLevelizedTfo_rec( pFanout, vLevels );
    }
    return vLevels;
}


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

  Synopsis    [Recursively counts the number of logic levels of one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Abc_NtkLevel_rec( Abc_Obj_t * pNode )
{
    Abc_Obj_t * pNext;
    int i, Level;
    assert( !Abc_ObjIsNet(pNode) );
    // skip the PI
    if ( Abc_ObjIsCi(pNode) )
        return pNode->Level;
    assert( Abc_ObjIsNode( pNode ) || pNode->Type == ABC_OBJ_CONST1);
    // if this node is already visited, return
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return pNode->Level;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // visit the transitive fanin
    pNode->Level = 0;
    Abc_ObjForEachFanin( pNode, pNext, i )
    {
        Level = Abc_NtkLevel_rec( Abc_ObjFanin0Ntk(pNext) );
        if ( pNode->Level < (unsigned)Level )
            pNode->Level = Level;
    }
    if ( Abc_ObjFaninNum(pNode) > 0 )
        pNode->Level++;
    return pNode->Level;
}

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

  Synopsis    [Recursively counts the number of logic levels of one node.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Abc_NtkLevelReverse_rec( Abc_Obj_t * pNode )
{
    Abc_Obj_t * pNext;
    int i, Level;
    assert( !Abc_ObjIsNet(pNode) );
    // skip the PI
    if ( Abc_ObjIsCo(pNode) )
        return pNode->Level;
    assert( Abc_ObjIsNode( pNode ) || pNode->Type == ABC_OBJ_CONST1);
    // if this node is already visited, return
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return pNode->Level;
    // mark the node as visited
    Abc_NodeSetTravIdCurrent( pNode );
    // visit the transitive fanin
    pNode->Level = 0;
    Abc_ObjForEachFanout( pNode, pNext, i )
    {
        Level = Abc_NtkLevelReverse_rec( Abc_ObjFanout0Ntk(pNext) );
        if ( pNode->Level < (unsigned)Level )
            pNode->Level = Level;
    }
    if ( Abc_ObjFaninNum(pNode) > 0 )
        pNode->Level++;
    return pNode->Level;
}

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

  Synopsis    [Computes the number of logic levels not counting PIs/POs.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
Vec_Vec_t * Abc_NtkLevelize( Abc_Ntk_t * pNtk )
{
    Abc_Obj_t * pObj;
    Vec_Vec_t * vLevels;
    int nLevels, i;
    nLevels = Abc_NtkLevel( pNtk );
    vLevels = Vec_VecStart( nLevels + 1 );
    Abc_NtkForEachNode( pNtk, pObj, i )
    {
        assert( (int)pObj->Level <= nLevels );
        Vec_VecPush( vLevels, pObj->Level, pObj );
    }
    return vLevels;
}

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

  Synopsis    [Computes the number of logic levels not counting PIs/POs.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Abc_NtkLevel( Abc_Ntk_t * pNtk )
{
    Abc_Obj_t * pNode;
    int i, LevelsMax;
    // set the CI levels to zero
    Abc_NtkForEachCi( pNtk, pNode, i )
        pNode->Level = 0;
    // perform the traversal
    LevelsMax = 0;
    Abc_NtkIncrementTravId( pNtk );
    Abc_NtkForEachNode( pNtk, pNode, i )
    {
        Abc_NtkLevel_rec( pNode );
        if ( LevelsMax < (int)pNode->Level )
            LevelsMax = (int)pNode->Level;
    }
    return LevelsMax;
}

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

  Synopsis    [Computes the number of logic levels not counting PIs/POs.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Abc_NtkLevelReverse( Abc_Ntk_t * pNtk )
{
    Abc_Obj_t * pNode;
    int i, LevelsMax;
    // set the CO levels to zero
    Abc_NtkForEachCo( pNtk, pNode, i )
        pNode->Level = 0;
    // perform the traversal
    LevelsMax = 0;
    Abc_NtkIncrementTravId( pNtk );
    Abc_NtkForEachNode( pNtk, pNode, i )
    {
        Abc_NtkLevelReverse_rec( pNode );
        if ( LevelsMax < (int)pNode->Level )
            LevelsMax = (int)pNode->Level;
    }
    return LevelsMax;
}

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

  Synopsis    [Recursively detects combinational loops.]

  Description []
                
  SideEffects []

  SeeAlso     []

***********************************************************************/
bool Abc_NtkIsAcyclic_rec( Abc_Obj_t * pNode )
{
    Abc_Ntk_t * pNtk = pNode->pNtk;
    Abc_Obj_t * pFanin;
    int fAcyclic, i;
    assert( !Abc_ObjIsNet(pNode) );
    if ( Abc_ObjIsCi(pNode) || Abc_ObjIsBox(pNode) || (Abc_NtkIsStrash(pNode->pNtk) && Abc_AigNodeIsConst(pNode)) )
        return 1;
    assert( Abc_ObjIsNode(pNode) );
    // make sure the node is not visited
    assert( !Abc_NodeIsTravIdPrevious(pNode) );
    // check if the node is part of the combinational loop
    if ( Abc_NodeIsTravIdCurrent(pNode) )
    {
        fprintf( stdout, "Network \"%s\" contains combinational loop!\n", Abc_NtkName(pNtk) );
        fprintf( stdout, "Node \"%s\" is encountered twice on the following path to the COs:\n", Abc_ObjName(pNode) );
        return 0;
    }
    // mark this node as a node on the current path
    Abc_NodeSetTravIdCurrent( pNode );
    // visit the transitive fanin
    Abc_ObjForEachFanin( pNode, pFanin, i )
    {
        pFanin = Abc_ObjFanin0Ntk(pFanin);
        // make sure there is no mixing of networks
        assert( pFanin->pNtk == pNode->pNtk );
        // check if the fanin is visited
        if ( Abc_NodeIsTravIdPrevious(pFanin) ) 
            continue;
        // traverse the fanin's cone searching for the loop
        if ( fAcyclic = Abc_NtkIsAcyclic_rec(pFanin) )
            continue;
        // return as soon as the loop is detected
        fprintf( stdout, " %s ->", Abc_ObjName(pFanin) );
        return 0;
    }
    // visit choices
    if ( Abc_NtkIsStrash(pNode->pNtk) && Abc_AigNodeIsChoice(pNode) )
    {
        for ( pFanin = pNode->pData; pFanin; pFanin = pFanin->pData )
        {
            // check if the fanin is visited
            if ( Abc_NodeIsTravIdPrevious(pFanin) ) 
                continue;
            // traverse the fanin's cone searching for the loop
            if ( fAcyclic = Abc_NtkIsAcyclic_rec(pFanin) )
                continue;
            // return as soon as the loop is detected
            fprintf( stdout, " %s", Abc_ObjName(pFanin) );
            fprintf( stdout, " (choice of %s) -> ", Abc_ObjName(pNode) );
            return 0;
        }
    }
    // mark this node as a visited node
    Abc_NodeSetTravIdPrevious( pNode );
    return 1;
}

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

  Synopsis    [Detects combinational loops.]

  Description [This procedure is based on the idea suggested by Donald Chai. 
  As we traverse the network and visit the nodes, we need to distinquish 
  three types of nodes: (1) those that are visited for the first time, 
  (2) those that have been visited in this traversal but are currently not 
  on the traversal path, (3) those that have been visited and are currently 
  on the travesal path. When the node of type (3) is encountered, it means 
  that there is a combinational loop. To mark the three types of nodes, 
  two new values of the traversal IDs are used.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
bool Abc_NtkIsAcyclic( Abc_Ntk_t * pNtk )
{
    Abc_Obj_t * pNode;
    int fAcyclic, i;
    // set the traversal ID for this DFS ordering
    Abc_NtkIncrementTravId( pNtk );   
    Abc_NtkIncrementTravId( pNtk );   
    // pNode->TravId == pNet->nTravIds      means "pNode is on the path"
    // pNode->TravId == pNet->nTravIds - 1  means "pNode is visited but is not on the path"
    // pNode->TravId <  pNet->nTravIds - 1  means "pNode is not visited"
    // traverse the network to detect cycles
    fAcyclic = 1;
    Abc_NtkForEachCo( pNtk, pNode, i )
    {
        pNode = Abc_ObjFanin0Ntk(Abc_ObjFanin0(pNode));
        if ( Abc_NodeIsTravIdPrevious(pNode) )
            continue;
        // traverse the output logic cone
        if ( fAcyclic = Abc_NtkIsAcyclic_rec(pNode) )
            continue;
        // stop as soon as the first loop is detected
        fprintf( stdout, " CO \"%s\"\n", Abc_ObjName(Abc_ObjFanout0(pNode)) );
        break;
    }
    return fAcyclic;
}


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

  Synopsis    [Analyses choice nodes.]

  Description []
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Abc_NodeSetChoiceLevel_rec( Abc_Obj_t * pNode, int fMaximum )
{
    Abc_Obj_t * pTemp;
    int Level1, Level2, Level, LevelE;
    // skip the visited node
    if ( Abc_NodeIsTravIdCurrent( pNode ) )
        return (int)pNode->pCopy;
    Abc_NodeSetTravIdCurrent( pNode );
    // compute levels of the children nodes
    Level1 = Abc_NodeSetChoiceLevel_rec( Abc_ObjFanin0(pNode), fMaximum );
    Level2 = Abc_NodeSetChoiceLevel_rec( Abc_ObjFanin1(pNode), fMaximum );
    Level  = 1 + ABC_MAX( Level1, Level2 );
    if ( pNode->pData )
    {
        LevelE = Abc_NodeSetChoiceLevel_rec( pNode->pData, fMaximum );
        if ( fMaximum )
            Level = ABC_MAX( Level, LevelE );
        else
            Level = ABC_MIN( Level, LevelE );
        // set the level of all equivalent nodes to be the same minimum
        for ( pTemp = pNode->pData; pTemp; pTemp = pTemp->pData )
            pTemp->pCopy = (void *)Level;
    }
    pNode->pCopy = (void *)Level;
    return Level;
}

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

  Synopsis    [Resets the levels of the nodes in the choice graph.]

  Description [Makes the level of the choice nodes to be equal to the
  maximum of the level of the nodes in the equivalence class. This way
  sorting by level leads to the reverse topological order, which is
  needed for the required time computation.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Abc_AigSetChoiceLevels( Abc_Ntk_t * pNtk )
{
    Abc_Obj_t * pObj;
    int i, LevelMax, LevelCur;
    assert( Abc_NtkIsStrash(pNtk) );
    // set the new travid counter
    Abc_NtkIncrementTravId( pNtk );
    // set levels of the CI and constant
    Abc_NtkForEachCi( pNtk, pObj, i )
    {
        Abc_NodeSetTravIdCurrent( pObj );
        pObj->pCopy = NULL;
    }
    pObj = Abc_AigConst1( pNtk );
    Abc_NodeSetTravIdCurrent( pObj );
    pObj->pCopy = NULL;
    // set levels of all other nodes
    LevelMax = 0;
    Abc_NtkForEachCo( pNtk, pObj, i )
    {
        LevelCur = Abc_NodeSetChoiceLevel_rec( Abc_ObjFanin0(pObj), 1 );
        LevelMax = ABC_MAX( LevelMax, LevelCur );
    }
    return LevelMax;
}

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

  Synopsis    [Returns nodes by level from the smallest to the largest.]

  Description [Correctly handles the case of choice nodes, by first
  spreading them out across several levels and then collecting.]
               
  SideEffects [What happens with dangling nodes???]

  SeeAlso     []

***********************************************************************/
Vec_Ptr_t * Abc_AigGetLevelizedOrder( Abc_Ntk_t * pNtk, int fCollectCis )
{
    Vec_Ptr_t * vNodes, * vLevels;
    Abc_Obj_t * pNode, ** ppHead;
    int LevelMax, i;
    assert( Abc_NtkIsStrash(pNtk) );
    // set the correct levels
    Abc_NtkCleanCopy( pNtk );
    LevelMax = Abc_AigSetChoiceLevels( pNtk );
    // relink nodes by level
    vLevels = Vec_PtrStart( LevelMax + 1 );
    Abc_NtkForEachNode( pNtk, pNode, i )
    {
        ppHead = ((Abc_Obj_t **)vLevels->pArray) + (int)pNode->pCopy;
        pNode->pCopy = *ppHead;
        *ppHead = pNode;
    }
    // recollect nodes
    vNodes = Vec_PtrStart( Abc_NtkNodeNum(pNtk) );
    Vec_PtrForEachEntryStart( vLevels, pNode, i, !fCollectCis )
        for ( ; pNode; pNode = pNode->pCopy )
            Vec_PtrPush( vNodes, pNode );
    Vec_PtrFree( vLevels );
    return vNodes;
}

////////////////////////////////////////////////////////////////////////
///                       END OF FILE                                ///
////////////////////////////////////////////////////////////////////////


