perf(levm): improve codecopy

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Perf
 
+### 2025-07-07
+
+- Improve CODECOPY opdcode handling [#3497](https://github.com/lambdaclass/ethrex/pull/3497)
+
 ### 2025-06-30
 
 - Use a stack pool [#3386](https://github.com/lambdaclass/ethrex/pull/3386)

crates/vm/levm/src/opcode_handlers/environment.rs

@@ -210,27 +210,49 @@ impl<'a> VM<'a> {
             return Ok(OpcodeResult::Continue { pc_increment: 1 });
         }
 
-        let mut data = vec![0u8; size];
+        // Here we verified indexing is in bounds.
+        #[expect(clippy::indexing_slicing, clippy::arithmetic_side_effects)]
         if code_offset < current_call_frame.bytecode.len().into() {
             let code_offset: usize = code_offset
                 .try_into()
                 .map_err(|_| InternalError::TypeConversion)?;
 
-            for (i, byte) in current_call_frame
-                .bytecode
-                .iter()
-                .skip(code_offset)
-                .take(size)
-                .enumerate()
-            {
-                if let Some(data_byte) = data.get_mut(i) {
-                    *data_byte = *byte;
-                }
+            let available = size.min(
+                current_call_frame
+                    .bytecode
+                    .len()
+                    .saturating_sub(code_offset),
+            );
+
+            if size <= 32 {
+                let mut data = [0u8; 32];
+
+                data[..available].copy_from_slice(
+                    &current_call_frame.bytecode[code_offset..code_offset + available],
+                );
+
+                memory::try_store_data(
+                    &mut current_call_frame.memory,
+                    destination_offset,
+                    &data[..size],
+                )?;
+            } else {
+                let mut data = vec![0u8; size];
+
+                data[..available].copy_from_slice(
+                    &current_call_frame.bytecode[code_offset..code_offset + available],
+                );
+
+                memory::try_store_data(&mut current_call_frame.memory, destination_offset, &data)?;
             }
+        } else {
+            memory::try_store_data(
+                &mut current_call_frame.memory,
+                destination_offset,
+                &vec![0u8; size],
+            )?;
         }
 
-        memory::try_store_data(&mut current_call_frame.memory, destination_offset, &data)?;
-
         Ok(OpcodeResult::Continue { pc_increment: 1 })
     }