fix(levm): keccak256 opcode (#1253)

Closes #1246.

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

@@ -31,14 +31,17 @@ impl VM {
 
         self.increase_consumed_gas(current_call_frame, gas_cost)?;
 
-        let value_bytes = current_call_frame.memory.load_range(offset, size)?;
+        let value_bytes = if size == 0 {
+            vec![]
+        } else {
+            current_call_frame.memory.load_range(offset, size)?
+        };
 
         let mut hasher = Keccak256::new();
         hasher.update(value_bytes);
-        let result = hasher.finalize();
         current_call_frame
             .stack
-            .push(U256::from_big_endian(&result))?;
+            .push(U256::from_big_endian(&hasher.finalize()))?;
 
         Ok(OpcodeSuccess::Continue)
     }

crates/vm/levm/tests/edge_case_tests.rs

@@ -1,3 +1,5 @@
+use std::str::FromStr;
+
 use bytes::Bytes;
 use ethrex_core::U256;
 use ethrex_levm::{
@@ -103,6 +105,22 @@ fn test_is_negative() {
     vm.execute(&mut current_call_frame);
 }
 
+#[test]
+fn test_non_compliance_keccak256() {
+    let mut vm = new_vm_with_bytecode(Bytes::copy_from_slice(&[88, 88, 32, 89])).unwrap();
+    let mut current_call_frame = vm.call_frames.pop().unwrap();
+    vm.execute(&mut current_call_frame);
+    assert_eq!(
+        *current_call_frame.stack.stack.first().unwrap(),
+        U256::from_str("0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470")
+            .unwrap()
+    );
+    assert_eq!(
+        *current_call_frame.stack.stack.get(1).unwrap(),
+        U256::zero()
+    );
+}
+
 #[test]
 fn test_sdiv_zero_dividend_and_negative_divisor() {
     let mut vm = new_vm_with_bytecode(Bytes::copy_from_slice(&[