implement the value opcode

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/src/lib.rs

@@ -188,6 +188,27 @@ mod tests {
         assert_eq!(received, expected);
     }
 
+    #[test]
+    fn transferred_value() {
+        sol!(
+            contract Value {
+                function value() public payable returns (uint);
+            }
+        );
+        let code = crate::compile_blob("Value", include_str!("../contracts/Value.sol"));
+        let mut state = State::new(Value::valueCall::SELECTOR.to_vec());
+        state.value = 0x1;
+
+        let (mut instance, export) = mock_runtime::prepare(&code, None);
+        let state = crate::mock_runtime::call(state, &mut instance, export);
+
+        assert_eq!(state.output.flags, 0);
+
+        let expected = I256::try_from(state.value).unwrap();
+        let received = I256::from_be_bytes::<32>(state.output.data.try_into().unwrap());
+        assert_eq!(received, expected);
+    }
+
     #[test]
     fn msize_non_word_sized_access() {
         sol!(

crates/integration/src/mock_runtime.rs

@@ -88,7 +88,7 @@ fn link_host_functions(engine: &Engine) -> Linker<State> {
             |caller: Caller<State>, out_ptr: u32, out_len_ptr: u32| -> Result<(), Trap> {
                 let (mut caller, state) = caller.split();
 
-                let value = state.value.encode();
+                let value = state.value.to_le_bytes();
 
                 caller.write_memory(out_ptr, &value)?;
                 caller.write_memory(out_len_ptr, &(value.len() as u32).encode())?;