From 5c39f3b5af4f2814505163adf62b40b5e42673ab Mon Sep 17 00:00:00 2001
From: Jared Burce <jaredr@gmail.com>
Date: Fri, 5 Mar 2021 05:06:15 -0800
Subject: [PATCH] emu ops can get multiple args, mem no longer implicit,
 implement RET

---
 src/emu/i8088.rs | 48 +++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 41 insertions(+), 7 deletions(-)

diff --git a/src/emu/i8088.rs b/src/emu/i8088.rs
index e9bff09..52a259f 100644
--- a/src/emu/i8088.rs
+++ b/src/emu/i8088.rs
@@ -56,26 +56,53 @@ mod ops {
     cpu.push16(mem, cpu.ip);
     cpu.ip = target;
   }
+
+  pub fn ret(cpu: &mut super::i8088, mem: &[u8]) {
+    trace!("RET");
+    cpu.ip = cpu.pop16(mem)
+  }
 }
 
 macro_rules! step {
-  (@code $cpu:ident, $bus:ident, ($name:ident, $cycles:literal, $arg:tt)) => {
-    step!(@$arg $name $cpu, $bus)
+  // Base case: all args processed and ready to call op
+  (@code ( $($args:tt)* ),
+         $cpu:ident, $bus:ident, $name:ident, $cycles:literal,
+         ()) => {
+    ops::$name($($args),*);
   };
 
-  (@rel16 $name:ident $cpu:ident, $bus:ident) => { {
+  // Inductive case: decode next arg to be placed in list
+  (@code ( $($args:tt)* ),
+         $cpu:ident, $bus:ident, $name:ident, $cycles:literal,
+         ($next:tt $($rest:tt)*)) => {
+    step!(@$next ( ($($args)*), $cpu, $bus, $name, $cycles, ($($rest)*) ), $cpu, $bus)
+  };
+
+  // accept an argument from a decoder and recur to look for next arg
+  (@arg ( ($($args:tt)*), $cpu:ident, $bus:ident, $name:ident, $cycles:literal, ( $($rest:tt)* ) ),
+        $arg:expr) => {
+    step!(@code ($($args)* $arg), $cpu, $bus, $name, $cycles, ( $($rest)* ))
+  };
+
+  // Argument Decoders
+
+  (@mem $cookie:tt, $cpu:ident, $bus:ident) => {
+    step!(@arg $cookie, &mut $bus.ram)
+  };
+
+  (@rel16 $cookie:tt, $cpu:ident, $bus:ident) => { {
     let mut buf = [0; 2];
     buf[0] = $cpu.next_ip($bus);
     buf[1] = $cpu.next_ip($bus);
-    ops::$name($cpu, &mut $bus.ram, LittleEndian::read_i16(&buf));
+    step!(@arg $cookie, LittleEndian::read_i16(&buf))
   } };
 
   // Entry Point
-  (($cpu:ident, $bus:ident) => { $( $code:literal => $impl:tt ),* } )  => {
+  (($cpu:ident, $bus:ident) => { $( $code:literal => $name:ident[$($args:tt),*] / $cycles:literal ),*$(,)? } )  => {
     {
       let opcode = $cpu.next_ip($bus);
       match(opcode) {
-        $( $code => step!(@code $cpu, $bus, $impl) )*,
+        $( $code => step!(@code ($cpu), $cpu, $bus, $name, $cycles, ($($args)*)) ),*,
         _ => unimplemented!("opcode: {:02X}", opcode)
       }
     }
@@ -91,7 +118,8 @@ impl i8088 {
   pub fn run(&mut self, bus: &mut Bus) {
     loop {
       step!((self, bus) => {
-        0xE8 => (call, 23, rel16)
+        0xC3 => ret[mem] / 20,
+        0xE8 => call[mem, rel16] / 23,
       })
     }
   }
@@ -102,6 +130,12 @@ impl i8088 {
     LittleEndian::write_u16(&mut mem[segoff_to_addr(self.ss, self.sp)..], val);
   }
 
+  fn pop16(&mut self, mem: &[u8]) -> u16 {
+    let val = LittleEndian::read_u16(&mem[segoff_to_addr(self.ss, self.sp)..]);
+    self.sp += 2;
+    val
+  }
+
   fn next_ip<'a>(&mut self, bus: &Bus) -> u8 {
     let eip = segoff_to_addr(self.cs, self.ip);
     self.ip += 1;