aig, gia: reduce the structural hash key without a divide

src/aig/aig/aigTable.c

@@ -36,14 +36,25 @@ ABC_NAMESPACE_IMPL_START
 // terms multiply a 0/1 flag by a small constant. Doing those two in unsigned
 // arithmetic is defined for every Id and keeps the result a function of the
 // operands alone.
-static unsigned long Aig_Hash( Aig_Obj_t * pObj, int TableSize ) 
+//
+// The mixed key is reduced to a bucket with two multiplies rather than with a
+// remainder, which is a hardware divide by a runtime value on the hottest path
+// this package has. The key is multiplied by an odd 64-bit constant and the
+// high half of the product taken, which every input bit has had an effect on;
+// that is then mapped onto the table by multiplying it by the table size and
+// taking the high half again. Neither step needs the size to be a power of
+// two: nTableSize is a public field and a client may size the table itself.
+#define AIG_HASH_MULT ABC_CONST(0x9E3779B97F4A7C15)
+
+static unsigned Aig_Hash( Aig_Obj_t * pObj, int TableSize )
 {
-    unsigned long Key = Aig_ObjIsExor(pObj) * 1699;
+    unsigned Key = Aig_ObjIsExor(pObj) * 1699, Hash;
     Key ^= (unsigned)Aig_ObjFanin0(pObj)->Id * 7937u;
     Key ^= (unsigned)Aig_ObjFanin1(pObj)->Id * 2971u;
     Key ^= Aig_ObjFaninC0(pObj) * 911;
     Key ^= Aig_ObjFaninC1(pObj) * 353;
-    return Key % TableSize;
+    Hash = (unsigned)(((word)Key * AIG_HASH_MULT) >> 32);
+    return (unsigned)(((word)Hash * (word)(unsigned)TableSize) >> 32);
 }
 
 // returns the place where this node is stored (or should be stored)
@@ -76,38 +87,34 @@ static Aig_Obj_t ** Aig_TableFind( Aig_Man_t * p, Aig_Obj_t * pObj )
 ***********************************************************************/
 void Aig_TableResize( Aig_Man_t * p )
 {
-    Aig_Obj_t * pEntry, * pNext;
-    Aig_Obj_t ** pTableOld, ** ppPlace;
-    int nTableSizeOld, Counter, i;
-    abctime clk;
+    Aig_Obj_t * pEntry;
+    Aig_Obj_t ** ppPlace;
+    int Counter, i;
     assert( p->pTable != NULL );
-clk = Abc_Clock();
-    // save the old table
-    pTableOld = p->pTable;
-    nTableSizeOld = p->nTableSize;
-    // get the new table
-    p->nTableSize = Abc_PrimeCudd( 2 * Aig_ManNodeNum(p) ); 
+    // The table is rebuilt from vObjs rather than from the old buckets, so
+    // the old array can be freed before the new one is allocated: the
+    // resize transient is max(old, new) instead of their sum, and the
+    // sweep reads the nodes sequentially where chain-chasing did not.
+    // Membership is unchanged -- the table holds exactly the AND and EXOR
+    // nodes, which is the invariant the Counter assert below has always
+    // stated, and the hash is recomputed from each node's fanins either
+    // way. Stale pNext values from the freed chains are never read: a
+    // node's pNext is only walked once it is in the new table, and it is
+    // nulled at insertion.
+    ABC_FREE( p->pTable );
+    p->nTableSize = Abc_PrimeCudd( 2 * Aig_ManNodeNum(p) );
     p->pTable = ABC_ALLOC( Aig_Obj_t *, p->nTableSize );
     memset( p->pTable, 0, sizeof(Aig_Obj_t *) * p->nTableSize );
-    // rehash the entries from the old table
     Counter = 0;
-    for ( i = 0; i < nTableSizeOld; i++ )
-    for ( pEntry = pTableOld[i], pNext = pEntry? pEntry->pNext : NULL; 
-          pEntry; pEntry = pNext, pNext = pEntry? pEntry->pNext : NULL )
+    Aig_ManForEachNode( p, pEntry, i )
     {
-        // get the place where this entry goes in the table 
         ppPlace = Aig_TableFind( p, pEntry );
         assert( *ppPlace == NULL ); // should not be there
-        // add the entry to the list
         *ppPlace = pEntry;
         pEntry->pNext = NULL;
         Counter++;
     }
     assert( Counter == Aig_ManNodeNum(p) );
-//    printf( "Increasing the structural table size from %6d to %6d. ", nTableSizeOld, p->nTableSize );
-//    ABC_PRT( "Time", Abc_Clock() - clk );
-    // replace the table and the parameters
-    ABC_FREE( pTableOld );
 }
 
 /**Function*************************************************************

src/aig/gia/giaHash.c

@@ -31,6 +31,12 @@ ABC_NAMESPACE_IMPL_START
 ///                     FUNCTION DEFINITIONS                         ///
 ////////////////////////////////////////////////////////////////////////
 
+// The mixed key is reduced to a bucket with two multiplies rather than with a
+// remainder, for the reason given over Aig_Hash() in aigTable.c: a remainder
+// by a runtime table size is a hardware divide on every lookup and every
+// insert, and this reduction needs no power-of-two table to avoid it.
+#define GIA_HASH_MULT ABC_CONST(0x9E3779B97F4A7C15)
+
 /**Function*************************************************************
 
   Synopsis    [Returns the place where this node is stored (or should be stored).]
@@ -44,12 +50,13 @@ ABC_NAMESPACE_IMPL_START
 ***********************************************************************/
 static inline int Gia_ManHashOne( int iLit0, int iLit1, int iLitC, int TableSize ) 
 {
-    unsigned Key = iLitC * 2011;
+    unsigned Key = iLitC * 2011, Hash;
     Key += Abc_Lit2Var(iLit0) * 7937;
     Key += Abc_Lit2Var(iLit1) * 2971;
     Key += Abc_LitIsCompl(iLit0) * 911;
     Key += Abc_LitIsCompl(iLit1) * 353;
-    return (int)(Key % TableSize);
+    Hash = (unsigned)(((word)Key * GIA_HASH_MULT) >> 32);
+    return (int)(((word)Hash * (word)(unsigned)TableSize) >> 32);
 }
 static inline int * Gia_ManHashFind( Gia_Man_t * p, int iLit0, int iLit1, int iLitC )
 {