abc/src/opt/fxu/fxuReduce.c

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

  FileName    [fxuReduce.c]

  PackageName [MVSIS 2.0: Multi-valued logic synthesis system.]

  Synopsis    [Procedures to reduce the number of considered cube pairs.]

  Author      [MVSIS Group]
  
  Affiliation [UC Berkeley]

  Date        [Ver. 1.0. Started - February 1, 2003.]

  Revision    [$Id: fxuReduce.c,v 1.0 2003/02/01 00:00:00 alanmi Exp $]

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

#include "base/abc/abc.h"
#include "fxuInt.h"
#include "fxu.h"

ABC_NAMESPACE_IMPL_START


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

static int Fxu_CountPairDiffs( char * pCover, unsigned char pDiffs[] );

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///                     FUNCTION DEFINITIONS                         ///
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/**Function*************************************************************

  Synopsis    [Precomputes the pairs to use for creating two-cube divisors.]

  Description [This procedure takes the matrix with variables and cubes 
  allocated (p), the original covers of the nodes (i-sets) and their number 
  (ppCovers,nCovers). The maximum number of pairs to compute and the total 
  number of pairs in existence. This procedure adds to the storage of
  divisors exactly the given number of pairs (nPairsMax) while taking
  first those pairs that have the smallest number of literals in their
  cube-free form.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Fxu_PreprocessCubePairs( Fxu_Matrix * p, Vec_Ptr_t * vCovers, int nPairsTotal, int nPairsMax )
{
    unsigned char * pnLitsDiff;   // storage for the counters of diff literals
    int * pnPairCounters;         // the counters of pairs for each number of diff literals
    Fxu_Cube * pCubeFirst, * pCubeLast;
    Fxu_Cube * pCube1, * pCube2;
    Fxu_Var * pVar;
    int nCubes, nBitsMax, nSum;
    int CutOffNum = -1, CutOffQuant = -1; // Suppress "might be used uninitialized"
    int iPair, iQuant, k, c;
//    clock_t clk = clock();
    char * pSopCover;
    int nFanins;

    assert( nPairsMax < nPairsTotal );

    // allocate storage for counter of diffs
    pnLitsDiff = ABC_FALLOC( unsigned char, nPairsTotal );
    // go through the covers and precompute the distances between the pairs
    iPair    =  0;
    nBitsMax = -1;
    for ( c = 0; c < vCovers->nSize; c++ )
        if ( (pSopCover = (char *)vCovers->pArray[c]) )
        {
            nFanins = Abc_SopGetVarNum(pSopCover);
            // precompute the differences
            Fxu_CountPairDiffs( pSopCover, pnLitsDiff + iPair );
            // update the counter
            nCubes = Abc_SopGetCubeNum( pSopCover );
            iPair += nCubes * (nCubes - 1) / 2;
            if ( nBitsMax < nFanins )
                nBitsMax = nFanins;
        }
    assert( iPair == nPairsTotal );

    // allocate storage for counters of cube pairs by difference
    pnPairCounters = ABC_FALLOC( int, 2 * nBitsMax );
    memset( pnPairCounters, 0, sizeof(int) * 2 * nBitsMax );
    // count the number of different pairs
    for ( k = 0; k < nPairsTotal; k++ )
        pnPairCounters[ pnLitsDiff[k] ]++;
    // determine what pairs to take starting from the lower
    // so that there would be exactly pPairsMax pairs
    if ( pnPairCounters[0] != 0 )
    {
        ABC_FREE( pnLitsDiff );
        ABC_FREE( pnPairCounters );
        printf( "The SOPs of the nodes contain duplicated cubes. Run \"bdd; sop\" before \"fx\".\n" );
        return 0;
    }
    if ( pnPairCounters[1] != 0 )
    {
        ABC_FREE( pnLitsDiff );
        ABC_FREE( pnPairCounters );
        printf( "The SOPs of the nodes are not SCC-free. Run \"bdd; sop\" before \"fx\".\n" );
        return 0;
    }
    assert( pnPairCounters[0] == 0 ); // otherwise, covers are not dup-free
    assert( pnPairCounters[1] == 0 ); // otherwise, covers are not SCC-free
    nSum = 0;
    for ( k = 0; k < 2 * nBitsMax; k++ )
    {
        nSum += pnPairCounters[k];
        if ( nSum >= nPairsMax )
        {
            CutOffNum   = k;
            CutOffQuant = pnPairCounters[k] - (nSum - nPairsMax);
            break;
        }
    }
    ABC_FREE( pnPairCounters );

    // set to 0 all the pairs above the cut-off number and quantity
    iQuant = 0;
    iPair  = 0;
    for ( k = 0; k < nPairsTotal; k++ )
        if ( pnLitsDiff[k] > CutOffNum ) 
            pnLitsDiff[k] = 0;
        else if ( pnLitsDiff[k] == CutOffNum )
        {
            if ( iQuant++ >= CutOffQuant )
                pnLitsDiff[k] = 0;
            else
                iPair++;
        }
        else
            iPair++;
    assert( iPair == nPairsMax );

    // collect the corresponding pairs and add the divisors
    iPair = 0;
    for ( c = 0; c < vCovers->nSize; c++ )
        if ( (pSopCover = (char *)vCovers->pArray[c]) )
        {
            // get the var
            pVar = p->ppVars[2*c+1];
            // get the first cube
            pCubeFirst = pVar->pFirst;
            // get the last cube
            pCubeLast = pCubeFirst;
            for ( k = 0; k < pVar->nCubes; k++ )
                pCubeLast = pCubeLast->pNext;
            assert( pCubeLast == NULL || pCubeLast->pVar != pVar );

            // go through the cube pairs
            for ( pCube1 = pCubeFirst; pCube1 != pCubeLast; pCube1 = pCube1->pNext )
                for ( pCube2 = pCube1->pNext; pCube2 != pCubeLast; pCube2 = pCube2->pNext )
                    if ( pnLitsDiff[iPair++] )
                    {   // create the divisors for this pair
                        Fxu_MatrixAddDivisor( p, pCube1, pCube2 );
                    }
        }
    assert( iPair == nPairsTotal );
    ABC_FREE( pnLitsDiff );
//ABC_PRT( "Preprocess", clock() - clk );
    return 1;
}


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

  Synopsis    [Counts the differences in each cube pair in the cover.]

  Description [Takes the cover (pCover) and the array where the
  diff counters go (pDiffs). The array pDiffs should have as many
  entries as there are different pairs of cubes in the cover: n(n-1)/2.
  Fills out the array pDiffs with the following info: For each cube
  pair, included in the array is the number of literals in both cubes
  after they are made cube free.]
               
  SideEffects []

  SeeAlso     []

***********************************************************************/
int Fxu_CountPairDiffs( char * pCover, unsigned char pDiffs[] )
{
    char * pCube1, * pCube2;
    int nOnes, nCubePairs, nFanins, v;
    nCubePairs = 0;
    nFanins = Abc_SopGetVarNum(pCover);
    Abc_SopForEachCube( pCover, nFanins, pCube1 )
    Abc_SopForEachCube( pCube1, nFanins, pCube2 )
    {
        if ( pCube1 == pCube2 )
            continue;
        nOnes = 0;
        for ( v = 0; v < nFanins; v++ )
            nOnes += (pCube1[v] != pCube2[v]);
        pDiffs[nCubePairs++] = nOnes;
    }
    return 1;
}

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///                       END OF FILE                                ///
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ABC_NAMESPACE_IMPL_END