ft(interpreter): impl push/pop

src/interpreter/register.rs

@@ -1,6 +1,8 @@
 use crate::operands::{Byte, ImmediateOperand, Word};
 use core::fmt;
 
+use super::interpreter::InterpreterError;
+
 #[derive(Debug, Clone, Copy)]
 pub struct Register {
     pub ax: AX,
@@ -20,13 +22,33 @@ impl Register {
             bx: BX::new(),
             cx: CX::new(),
             dx: DX::new(),
-            sp: 0,
+            sp: 0xffff,
             bp: 0,
             si: 0,
             di: 0,
         }
     }
 
+    /// Decrement stack pointer
+    pub fn push(&mut self) -> Result<(), InterpreterError> {
+        if self.sp <= 2 {
+            return Err(InterpreterError::InvalidRegisterState(*self));
+        } else {
+            self.sp -= 2;
+            Ok(())
+        }
+    }
+
+    /// Increment stack pointer
+    pub fn pop(&mut self) -> Result<(), InterpreterError> {
+        if self.sp >= 0xffff - 2 {
+            return Err(InterpreterError::InvalidRegisterState(*self));
+        } else {
+            self.sp += 2;
+            Ok(())
+        }
+    }
+
     /// Read value from a [`crate::register::Register`].
     pub fn read(&self, reg: crate::register::Register) -> ImmediateOperand {
         match reg {