# UNDF: UNDF-2026-000001046
# UNDF: UNDF-2026-XXXXXXXXX
--- a/src/cheat.cpp
+++ b/src/cheat.cpp
@@ -67,6 +67,10 @@ CHEATF_SUBFAST SubCheats[256];
 uint32 numsubcheats = 0;
 int globalCheatDisabled = 0;
 int disableAutoLSCheats = 0;
 bool disableShowGG = 0;
 static _8BYTECHEATMAP* cheatMap = NULL;
 struct CHEATF *cheats = 0, *cheatsl = 0;
+
+// O(1) direct-address lookup replacing the O(C) SubCheats[] linear scan.
+// Index -1 means no cheat at this address.
+static int cheat_idx[0x10000];


 #define CHEATC_NONE     0x8000
@@ -79,16 +83,16 @@ static uint16 *CheatComp = 0;

 static DECLFR(SubCheatsRead)
 {
-	CHEATF_SUBFAST *s = SubCheats;
-	int x=numsubcheats;
-
-	do
-	{
-		if(s->addr==A)
-		{
-			if(s->compare>=0)
-			{
-				uint8 pv=s->PrevRead(A);
-
-				if(pv==s->compare)
-					return(s->val);
-				else return(pv);
-			}
-			else return(s->val);
-		}
-		s++;
-	} while(--x);
-	return(0);	/* We should never get here. */
+	// O(1): look up this address directly instead of scanning all active cheats.
+	int idx = cheat_idx[A];
+	if(idx < 0) return(0); /* should never happen if installed correctly */
+	CHEATF_SUBFAST *s = &SubCheats[idx];
+	if(s->compare>=0)
+	{
+		uint8 pv=s->PrevRead(A);
+		if(pv==s->compare)
+			return(s->val);
+		else return(pv);
+	}
+	return(s->val);
 }

 void RebuildSubCheats(void)
@@ -96,6 +100,8 @@ void RebuildSubCheats(void)
 	uint32 x;
 	struct CHEATF *c = cheats;
+	// Clear the direct-lookup table for addresses we're about to remove.
 	for (x = 0; x < numsubcheats; x++)
 	{
+		cheat_idx[SubCheats[x].addr] = -1;
 		SetReadHandler(SubCheats[x].addr, SubCheats[x].addr, SubCheats[x].PrevRead);
 		if (cheatMap)
 			FCEUI_SetCheatMapByte(SubCheats[x].addr, false);
@@ -113,6 +119,7 @@ void RebuildSubCheats(void)
 			SubCheats[numsubcheats].val = c->val;
 			SubCheats[numsubcheats].compare = c->compare;
 			SetReadHandler(c->addr, c->addr, SubCheatsRead);
+			cheat_idx[c->addr] = (int)numsubcheats;
 			if (cheatMap)
 				FCEUI_SetCheatMapByte(SubCheats[numsubcheats].addr, true);
 			numsubcheats++;
@@ -123,6 +130,14 @@ void RebuildSubCheats(void)
 	FrozenAddressCount = numsubcheats;
 }

+// Call once at startup to initialise the direct-lookup table.
+void FCEU_CheatIdxInit(void)
+{
+	for(int i = 0; i < 0x10000; i++)
+		cheat_idx[i] = -1;
+}