diff --git a/README.md b/README.md
index 6d676b5..f9c62da 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ While reading [Crafting Interpreters](https://craftinginterpreters.com/), after
 - [x] 27 - Classes and Instances
 - [x] 28 - Method and Initializers
 - [x] 29 - Superclasses
-- [ ] 30 - Optimization
+- [x] 30 - Optimization (without NaN boxing/NaN tagging)
 
 ## Build & run
 
diff --git a/src/constant.zig b/src/constant.zig
index 83d1904..0f390ff 100644
--- a/src/constant.zig
+++ b/src/constant.zig
@@ -10,14 +10,14 @@ pub const UINT8_COUNT = UINT8_MAX + 1;
 pub const FRAMES_MAX = 64;
 pub const STACK_MAX = (FRAMES_MAX * UINT8_MAX);
 
-pub const DEBUG_PRINT_CODE = true;
-pub const DEBUG_TRACE_EXECUTION = true;
+pub const DEBUG_PRINT_CODE = false;
+pub const DEBUG_TRACE_EXECUTION = false;
 pub const DEBUG_PRINT_INTERNAL_STRINGS = false;
 pub const DEBUG_PRINT_GLOBALS = false;
 
 pub const DEBUG_STRESS_GC = true;
 pub const DEBUG_LOG_GC = false;
 
-pub const USE_CUSTON_ALLOCATOR = false;
+pub const USE_CUSTON_ALLOCATOR = true;
 
 pub const GC_HEAP_GROW_FACTOR = 2;
diff --git a/src/table.zig b/src/table.zig
index 6ad4847..0af9747 100644
--- a/src/table.zig
+++ b/src/table.zig
@@ -61,7 +61,8 @@ pub const Table = struct {
 
     pub fn find_entry(entries: []Entry, key: *Obj.String) ?*Entry {
         var tombstone: ?*Entry = null;
-        var index = key.hash % entries.len;
+        // var index = key.hash % entries.len;
+        var index = key.hash & (entries.len - 1);
 
         while (true) {
             const entry = &entries[index];
@@ -84,7 +85,8 @@ pub const Table = struct {
                 return entry;
             }
 
-            index = (index + 1) % entries.len;
+            // index = (index + 1) % entries.len;
+            index = (index + 1) & (entries.len - 1);
         }
     }
 
@@ -179,7 +181,8 @@ pub const Table = struct {
             return null;
         }
 
-        var index = hash % self.capacity;
+        // var index = hash % self.capacity;
+        var index = hash & (self.capacity - 1);
         while (true) {
             const entry = &self.entries[index];
             if (entry.key == null) {
@@ -191,7 +194,8 @@ pub const Table = struct {
                 return entry.key;
             }
 
-            index = (index + 1) % self.capacity;
+            // index = (index + 1) % self.capacity;
+            index = (index + 1) & (self.capacity - 1);
         }
     }
 };