Allow pushing negative addresses.

src/parse.rs

@@ -29,10 +29,8 @@ pub fn parse(stack: &mut Stack, file_content: &str) {
                 arg = splited_data.get(0).unwrap().clone();
             } else if name.chars().nth(0) == Some('$') || name.chars().nth(1) == Some('$') {
                 arg = command[1].clone();
-            } else if command[1] == "-1" { // required for
-                data = 65535;              // _unix_random
-            } else if let Ok(number) = command[1].parse() {
-                data = number;
+            } else if let Ok(number) = command[1].parse::<i32>() {
+                data = number as u16;
             } else {
                 eprintln!("{}", ParseError::ArgumentNotRequired(command[0].to_string(), i + 1, line.to_string()));
                 std::process::exit(2);
@@ -42,4 +40,4 @@ pub fn parse(stack: &mut Stack, file_content: &str) {
         let inst = Instruction { name, arg, data };
         stack.program.push(inst);
     }
-}
+}