From a6066d1fdf00689922b6f8979ac81c1071640d3e Mon Sep 17 00:00:00 2001
From: John <j@soft.fish>
Date: Tue, 9 Jul 2024 01:05:21 -0500
Subject: [PATCH] Implement DAA

---
 src/cpu.rs | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index 912f0e5..a63536a 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -414,7 +414,26 @@ mod instructions {
     /// Funky instructions
     impl CPU {
         pub fn daa(&mut self) -> IResult {
-            Err(UnimplementedInsn(self.ir))?
+            let mut carry = false;
+            let mut adjusted = self[R8::A];
+            let previous = adjusted.0;
+            let flags = self.flags();
+            // ones digit: if there was a carry out, or the value *grew* too large
+            if flags.h() || (!flags.n() && previous & 0xf > 9) {
+                adjusted += 0x06;
+            }
+            // tens digit:  if there was a carry out, or the value *grew* too large
+            if flags.c() || (!flags.n() && previous >> 4 > 9) {
+                adjusted += 0x60;
+                carry = true;
+            }
+            adjusted += previous;
+            self[R8::A] = adjusted;
+
+            let flags = self.flags_mut();
+            *flags = flags.with_z(adjusted.0 == 0).with_h(false).with_c(carry);
+
+            Ok(())
         }
         pub fn cpl(&mut self) -> IResult {
             self[R8::A] ^= 0xff;