diff --git a/src/map/if/acd/ac_wrapper.cpp b/src/map/if/acd/ac_wrapper.cpp
index 7268fcad4..441cb7008 100644
--- a/src/map/if/acd/ac_wrapper.cpp
+++ b/src/map/if/acd/ac_wrapper.cpp
@@ -70,18 +70,18 @@ int acd_decompose( word * pTruth, unsigned nVars, int lutSize, unsigned *pdelay,
   return 0;
 }
 
-int acd66_evaluate( word * pTruth, unsigned nVars, int verify )
+int acd66_evaluate( word * pTruth, unsigned nVars, int compute_decomposition )
 {
   using namespace acd;
 
   acd66_params ps;
-  ps.verify = static_cast<bool>( verify );
+  ps.verify = false;
   acd66_impl acd( nVars, ps );
 
   if ( acd.run( pTruth ) == 0 )
     return 0;
   
-  if ( !verify )
+  if ( !compute_decomposition )
     return 1;
 
   int val = acd.compute_decomposition();
diff --git a/src/map/if/acd/ac_wrapper.h b/src/map/if/acd/ac_wrapper.h
index 2b832c287..2e052c563 100644
--- a/src/map/if/acd/ac_wrapper.h
+++ b/src/map/if/acd/ac_wrapper.h
@@ -28,7 +28,7 @@ ABC_NAMESPACE_HEADER_START
 int acd_evaluate( word * pTruth, unsigned nVars, int lutSize, unsigned *pdelay, unsigned *cost, int try_no_late_arrival );
 int acd_decompose( word * pTruth, unsigned nVars, int lutSize, unsigned *pdelay, unsigned char *decomposition );
 
-int acd66_evaluate( word * pTruth, unsigned nVars, int verify );
+int acd66_evaluate( word * pTruth, unsigned nVars, int compute_decomposition );
 int acd66_decompose( word * pTruth, unsigned nVars, unsigned char *decomposition );
 
 ABC_NAMESPACE_HEADER_END
diff --git a/src/map/if/acd/acd66.hpp b/src/map/if/acd/acd66.hpp
index a1369db83..166402ca0 100644
--- a/src/map/if/acd/acd66.hpp
+++ b/src/map/if/acd/acd66.hpp
@@ -54,7 +54,7 @@ struct acd66_params
   uint32_t max_evaluations{ 3 };
 
   /*! \brief Run verification before returning. */
-  bool verify{ true };
+  bool verify{ false };
 };
 
 /*! \brief Statistics for acd66 */
diff --git a/src/map/if/ifDec66.c b/src/map/if/ifDec66.c
index 932f5feb2..3a836363d 100644
--- a/src/map/if/ifDec66.c
+++ b/src/map/if/ifDec66.c
@@ -1,6 +1,6 @@
 /**CFile****************************************************************
 
-  FileName    [ifDec16.c]
+  FileName    [ifDec66.c]
 
   SystemName  [ABC: Logic synthesis and verification system.]
 
@@ -8,13 +8,13 @@
 
   Synopsis    [Fast checking procedures.]
 
-  Author      [Alan Mishchenko]
+  Author      [Alessandro Tempia Calvino]
   
-  Affiliation [UC Berkeley]
+  Affiliation [EPFL]
 
-  Date        [Ver. 1.0. Started - November 21, 2006.]
+  Date        [Ver. 1.0. Started - Feb 8, 2024.]
 
-  Revision    [$Id: ifDec16.c,v 1.00 2006/11/21 00:00:00 alanmi Exp $]
+  Revision    [$Id: ifDec66.c,v 1.00 2008/02/08 00:00:00 tempia Exp $]
 
 ***********************************************************************/
 
@@ -24,10 +24,258 @@
 
 ABC_NAMESPACE_IMPL_START
 
+#define CLU_VAR_MAX  16
+#define CLU_MEM_MAX  1000  // 1 GB
+#define CLU_UNUSED   0xff
+
+////////////////////////////////////////////////////////////////////////
+///                        DECLARATIONS                              ///
+////////////////////////////////////////////////////////////////////////
+
+// decomposition
+typedef struct If_Grp_t_ If_Grp_t;
+struct If_Grp_t_
+{
+    char       nVars;
+    char       nMyu;
+    char       pVars[CLU_VAR_MAX];
+};
+
+// hash table entry
+typedef struct If_Hte_t_ If_Hte_t;
+struct If_Hte_t_
+{
+    If_Hte_t * pNext;
+    unsigned   Group;
+    unsigned   Counter;
+    word       pTruth[1];
+};
+
 ////////////////////////////////////////////////////////////////////////
 ///                     FUNCTION DEFINITIONS                         ///
 ////////////////////////////////////////////////////////////////////////
 
+static inline unsigned If_CluGrp2Uns2( If_Grp_t * pG )
+{
+    char * pChar = (char *)pG;
+    unsigned Res = 0;
+    int i;
+    for ( i = 0; i < 8; i++ )
+        Res |= ((pChar[i] & 15) << (i << 2));
+    return Res;
+}
+
+static inline void If_CluUns2Grp2( unsigned Group, If_Grp_t * pG )
+{
+    char * pChar = (char *)pG;
+    int i;
+    for ( i = 0; i < 8; i++ )
+        pChar[i] = ((Group >> (i << 2)) & 15);
+}
+
+unsigned int If_CluPrimeCudd2( unsigned int p )
+{
+    int i,pn;
+
+    p--;
+    do {
+        p++;
+        if (p&1) {
+        pn = 1;
+        i = 3;
+        while ((unsigned) (i * i) <= p) {
+        if (p % i == 0) {
+            pn = 0;
+            break;
+        }
+        i += 2;
+        }
+    } else {
+        pn = 0;
+    }
+    } while (!pn);
+    return(p);
+
+} /* end of Cudd_Prime */
+
+// hash table
+static inline int If_CluWordNum2( int nVars )
+{
+    return nVars <= 6 ? 1 : 1 << (nVars-6);
+}
+
+int If_CluHashFindMedian2( If_Man_t * p, int t )
+{
+    If_Hte_t * pEntry;
+    Vec_Int_t * vCounters;
+    int i, Max = 0, Total = 0, Half = 0;
+    vCounters = Vec_IntStart( 1000 );
+    for ( i = 0; i < p->nTableSize[t]; i++ )
+    {
+        for ( pEntry = ((If_Hte_t **)p->pHashTable[t])[i]; pEntry; pEntry = pEntry->pNext )
+        {
+            if ( Max < (int)pEntry->Counter )
+            {
+                Max = pEntry->Counter;
+                Vec_IntSetEntry( vCounters, pEntry->Counter, 0 );
+            }
+            Vec_IntAddToEntry( vCounters, pEntry->Counter, 1 );
+            Total++;
+        }
+    }
+    for ( i = Max; i > 0; i-- )
+    {
+        Half += Vec_IntEntry( vCounters, i );
+        if ( Half > Total/2 )
+            break;
+    }
+/*
+    printf( "total = %d  ", Total );
+    printf( "half = %d  ", Half );
+    printf( "i = %d  ", i );
+    printf( "Max = %d.\n", Max );
+*/
+    Vec_IntFree( vCounters );
+    return Abc_MaxInt( i, 1 );
+}
+
+int If_CluHashKey2( word * pTruth, int nWords, int Size )
+{
+    static unsigned BigPrimes[8] = {12582917, 25165843, 50331653, 100663319, 201326611, 402653189, 805306457, 1610612741};
+    unsigned Value = 0;
+    int i;
+    if ( nWords < 4 )
+    {
+        unsigned char * s = (unsigned char *)pTruth;
+        for ( i = 0; i < 8 * nWords; i++ )
+            Value ^= BigPrimes[i % 7] * s[i];
+    }
+    else
+    {
+        unsigned * s = (unsigned *)pTruth;
+        for ( i = 0; i < 2 * nWords; i++ )
+            Value ^= BigPrimes[i % 7] * s[i];
+    }
+    return Value % Size;
+}
+
+unsigned * If_CluHashLookup2( If_Man_t * p, word * pTruth, int t )
+{
+    If_Hte_t * pEntry, * pPrev;
+    int nWords, HashKey;
+    if ( p == NULL )
+        return NULL;
+    nWords = If_CluWordNum2(p->pPars->nLutSize);
+    if ( p->pMemEntries == NULL )
+        p->pMemEntries = Mem_FixedStart( sizeof(If_Hte_t) + sizeof(word) * (If_CluWordNum2(p->pPars->nLutSize) - 1) );
+    if ( p->pHashTable[t] == NULL )
+    {
+        // decide how large should be the table
+        int nEntriesMax1 = 4 * If_CluPrimeCudd2( Vec_PtrSize(p->vObjs) * p->pPars->nCutsMax );
+        int nEntriesMax2 = (int)(((double)CLU_MEM_MAX * (1 << 20)) / If_CluWordNum2(p->pPars->nLutSize) / 8);
+//        int nEntriesMax2 = 10000;
+        // create table
+        p->nTableSize[t] = If_CluPrimeCudd2( Abc_MinInt(nEntriesMax1, nEntriesMax2)/2 );
+        p->pHashTable[t] = ABC_CALLOC( void *, p->nTableSize[t] );
+    }
+    // check if this entry exists
+    HashKey = If_CluHashKey2( pTruth, nWords, p->nTableSize[t] );
+    for ( pEntry = ((If_Hte_t **)p->pHashTable[t])[HashKey]; pEntry; pEntry = pEntry->pNext )
+        if ( memcmp(pEntry->pTruth, pTruth, sizeof(word) * nWords) == 0 )
+        {
+            pEntry->Counter++;
+            return &pEntry->Group;
+        }
+    // resize the hash table
+    if ( p->nTableEntries[t] >= 2 * p->nTableSize[t] )
+    {
+        // collect useful entries
+        If_Hte_t * pPrev;
+        Vec_Ptr_t * vUseful = Vec_PtrAlloc( p->nTableEntries[t] );
+        int i, Median = If_CluHashFindMedian2( p, t );
+        for ( i = 0; i < p->nTableSize[t]; i++ )
+        {
+            for ( pEntry = ((If_Hte_t **)p->pHashTable[t])[i]; pEntry; )
+            {
+                if ( (int)pEntry->Counter > Median )
+                {
+                    Vec_PtrPush( vUseful, pEntry );
+                    pEntry = pEntry->pNext;
+                }
+                else
+                {
+                    pPrev = pEntry->pNext;
+                    Mem_FixedEntryRecycle( p->pMemEntries, (char *)pEntry );
+                    pEntry = pPrev;
+                }
+            }
+        }
+        // add useful entries
+        memset( p->pHashTable[t], 0, sizeof(void *) * p->nTableSize[t] );
+        Vec_PtrForEachEntry( If_Hte_t *, vUseful, pEntry, i )
+        {
+            HashKey = If_CluHashKey2( pEntry->pTruth, nWords, p->nTableSize[t] );
+            pPrev = ((If_Hte_t **)p->pHashTable[t])[HashKey];
+            if ( pPrev == NULL || pEntry->Counter >= pPrev->Counter )
+            {
+                pEntry->pNext = pPrev;
+                ((If_Hte_t **)p->pHashTable[t])[HashKey] = pEntry;
+            }
+            else
+            {
+                while ( pPrev->pNext && pEntry->Counter < pPrev->pNext->Counter )
+                    pPrev = pPrev->pNext;
+                pEntry->pNext = pPrev->pNext;
+                pPrev->pNext = pEntry;
+            }
+        }
+        p->nTableEntries[t] = Vec_PtrSize( vUseful );
+        Vec_PtrFree( vUseful );
+    }
+    // create entry
+    p->nTableEntries[t]++;
+    pEntry = (If_Hte_t *)Mem_FixedEntryFetch( p->pMemEntries );
+    memcpy( pEntry->pTruth, pTruth, sizeof(word) * nWords );
+    pEntry->Group = CLU_UNUSED;
+    pEntry->Counter = 1;
+    // insert at the beginning
+//    pEntry->pNext = ((If_Hte_t **)p->pHashTable[t])[HashKey];
+//    ((If_Hte_t **)p->pHashTable[t])[HashKey] = pEntry;
+    // insert at the end
+    pEntry->pNext = NULL;
+    for ( pPrev = ((If_Hte_t **)p->pHashTable[t])[HashKey]; pPrev && pPrev->pNext; pPrev = pPrev->pNext );
+    if ( pPrev == NULL )
+        ((If_Hte_t **)p->pHashTable[t])[HashKey] = pEntry;
+    else
+        pPrev->pNext = pEntry;
+    return &pEntry->Group;
+}
+
+// returns if successful
+int If_CluCheck66( If_Man_t * p, word * pTruth0, int nVars, int fHashing )
+{
+    If_Grp_t G1 = {0};
+    unsigned * pHashed = NULL;
+
+    if ( p && fHashing )
+    {
+        pHashed = If_CluHashLookup2( p, pTruth0, 0 );
+        if ( pHashed && *pHashed != CLU_UNUSED )
+            If_CluUns2Grp2( *pHashed, &G1 );
+    }
+
+    /* new entry */
+    if ( G1.nVars == 0 )
+    {
+        G1.nVars = acd66_evaluate( pTruth0, nVars, 0 );
+    }
+
+    if ( pHashed )
+        *pHashed = If_CluGrp2Uns2( &G1 );
+
+    return G1.nVars;
+}
+
 /**Function*************************************************************
 
   Synopsis    [Performs ACD into 66 cascade.]
@@ -79,7 +327,7 @@ int If_CutPerformCheck66( If_Man_t * p, unsigned * pTruth0, int nVars, int nLeav
         return 1;
 
     // derive the decomposition
-    return (int)(acd66_evaluate( (word *)pTruth, nVars, 1 ) > 0 );
+    return If_CluCheck66(p, (word*)pTruth, nVars, 1);
 }
 
 ////////////////////////////////////////////////////////////////////////