# UNDF: UNDF-2026-000001055
# UNDF: UNDF-2026-XXXXXXXXX
--- a/Core/debugger.c
+++ b/Core/debugger.c
@@ -1421,6 +1421,8 @@ static unsigned should_break(GB_gameboy_t *gb, uint16_t addr, bool jump_to)
 static unsigned should_break(GB_gameboy_t *gb, uint16_t addr, bool jump_to)
 {
     if (unlikely(gb->backstep_instructions)) return false;
+    /* O(1) fast-path: no breakpoint registered at this address */
+    if (!gb->breakpoint_address_set[addr]) return 0;
     uint16_t bank = bank_for_addr(gb, addr);
     for (unsigned i = 0; i < gb->n_breakpoints; i++) {
         struct GB_breakpoint_s *breakpoint = &gb->breakpoints[i];
@@ -1093,6 +1093,10 @@ static bool breakpoint(GB_gameboy_t *gb, char *arguments, char *modifiers, const
     gb->breakpoints[gb->n_breakpoints++] = (struct GB_breakpoint_s){
         .id = id, .key = key, .condition = condition? strdup(condition) : NULL,
         .is_jump_to = is_jump_to, .length = length, .inclusive = inclusive,
     };
+    /* Mark all addresses covered by this breakpoint range in O(1) lookup */
+    for (uint32_t a = result.value; a <= (uint32_t)result.value + length + inclusive; a++) {
+        gb->breakpoint_address_set[(uint16_t)a] = true;
+    }

--- a/Core/gb.h
+++ b/Core/gb.h
@@ -749,6 +749,8 @@ struct GB_gameboy_internal_s {
         uint16_t n_breakpoints;
         struct GB_breakpoint_s *breakpoints;
         bool has_jump_to_breakpoints, has_software_breakpoints;
+        /* Boolean lookup table: true if any breakpoint covers this 16-bit address.
+           Provides O(1) per-instruction bail-out in should_break() hot path. */
+        bool breakpoint_address_set[0x10000];

--- a/Core/debugger.c (rebuild helper)
+++ b/Core/debugger.c (rebuild helper)
+static void rebuild_breakpoint_address_set(GB_gameboy_t *gb)
+{
+    memset(gb->breakpoint_address_set, 0, sizeof(gb->breakpoint_address_set));
+    for (unsigned i = 0; i < gb->n_breakpoints; i++) {
+        struct GB_breakpoint_s *bp = &gb->breakpoints[i];
+        for (uint32_t a = bp->addr; a <= (uint32_t)bp->addr + bp->length + bp->inclusive; a++) {
+            gb->breakpoint_address_set[(uint16_t)a] = true;
+        }
+    }
+}