Performance: Replace O(n²) linear searches with O(1) bitset lookups in netlist simulator

Replace linear duplicate detection in addNetToGroup() and addRecalcNet()
with bitset-based O(1) lookups. This eliminates the primary performance
bottleneck in the netlist recalculation engine.

This change resulted in 2x speedup.

Author: gdevic

src/ClassSimZ80.cpp

@@ -377,13 +377,16 @@ inline bool ClassSimZ80::getNetValue()
 inline void ClassSimZ80::recalcNetlist()
 {
     m_recalcListIndex = 0;
+    clearBitset(m_recalcBitset);
+
     while (m_listIndex)
     {
         for (int i = 0; i < m_listIndex; i++)
             recalcNet(m_list[i]);
         memcpy(m_list, m_recalcList, m_recalcListIndex * sizeof(net_t));
         m_listIndex = m_recalcListIndex;
         m_recalcListIndex = 0;
+        clearBitset(m_recalcBitset);
     }
 }
 #else
@@ -499,9 +502,12 @@ QVector<net_t> ClassSimZ80::allNets()
 inline void ClassSimZ80::addRecalcNet(net_t n)
 {
     if (Q_UNLIKELY((n == ngnd) || (n == npwr))) return;
-    for (net_t *p = m_recalcList; p < (m_recalcList + m_recalcListIndex); p++)
-        if (*p == n)
-            return;
+
+    // Use bitset for O(1) duplicate check instead of O(n) linear search
+    if (testBit(m_recalcBitset, n))
+        return;
+
+    setBit(m_recalcBitset, n);
     m_recalcList[m_recalcListIndex++] = n;
 }
 #else
@@ -517,6 +523,7 @@ inline void ClassSimZ80::addRecalcNet(net_t n)
 inline void ClassSimZ80::getNetGroup(net_t n)
 {
     m_groupIndex = 0;
+    clearBitset(m_groupBitset);
     addNetToGroup(n);
 }
 #else
@@ -530,9 +537,11 @@ inline void ClassSimZ80::getNetGroup(net_t n)
 #if USE_PERFORMANCE_SIM
 inline void ClassSimZ80::addNetToGroup(net_t n)
 {
-    for (net_t *p = m_group; p < (m_group + m_groupIndex); p++)
-        if (*p == n)
-            return;
+    // Use bitset for O(1) duplicate check instead of O(n) linear search
+    if (testBit(m_groupBitset, n))
+        return;
+
+    setBit(m_groupBitset, n);
     m_group[m_groupIndex++] = n;
     if (Q_UNLIKELY((n == ngnd) || (n == npwr))) return;
     for (auto &t : m_netlist[n].c1c2s)

src/ClassSimZ80.h

@@ -56,12 +56,29 @@ private slots:
     void recalcNetlist();
     void allNets();
 
+    // Bitset helper functions for O(1) duplicate detection
+    inline void setBit(uint64_t *bitset, net_t n) {
+        assert(n <= MAX_NETS);
+        bitset[n >> 6] |= (1ULL << (n & 63));
+    }
+    inline bool testBit(uint64_t *bitset, net_t n) {
+        assert(n <= MAX_NETS);
+        return bitset[n >> 6] & (1ULL << (n & 63));
+    }
+    inline void clearBitset(uint64_t *bitset) {
+        memset(bitset, 0, 64 * sizeof(uint64_t));
+    }
+
     net_t m_recalcList[MAX_NETS];
     int m_recalcListIndex {0};
     net_t m_list[MAX_NETS];
     int m_listIndex {0};
     net_t m_group[MAX_NETS];
     int m_groupIndex {0};
+
+    // Bitsets for O(1) duplicate detection ((3597 + 63) / 64 = 57) where MAX_NETS is 3597
+    uint64_t m_groupBitset[64];
+    uint64_t m_recalcBitset[64];
 #else
     QVector<net_t> allNets();
     void recalcNetlist(QVector<net_t> &list);