From 2c1ac1833484f8744658f256399b483cc956813c Mon Sep 17 00:00:00 2001
From: Washi <washiwashi1337@gmail.com>
Date: Wed, 25 Jul 2018 00:51:26 +0200
Subject: [PATCH] DAA now conforms to testroms.

---
 Emux.GameBoy/Cpu/GameBoyAlu.cs       | 39 ++++++++++++----------------
 Emux/Expressions/ExpressionParser.cs |  5 ++--
 2 files changed, 19 insertions(+), 25 deletions(-)

diff --git a/Emux.GameBoy/Cpu/GameBoyAlu.cs b/Emux.GameBoy/Cpu/GameBoyAlu.cs
index c5c0646..005b2ea 100644
--- a/Emux.GameBoy/Cpu/GameBoyAlu.cs
+++ b/Emux.GameBoy/Cpu/GameBoyAlu.cs
@@ -337,37 +337,32 @@ namespace Emux.GameBoy.Cpu
 
         internal void Daa()
         {
-            var flags = RegisterFlags.None;
+            // Reference: https://ehaskins.com/2018-01-30%20Z80%20DAA/
+            
+            int a = _registers.A;
 
-            int value = _registers.A;
+            int correction = 0;
+            var setFlagC = RegisterFlags.None;
 
-            int correction = _registers.GetFlags(RegisterFlags.C) ? 0x60 : 0x00;
-
-            if (_registers.GetFlags(RegisterFlags.H))
+            if (_registers.GetFlags(RegisterFlags.H) || (!_registers.GetFlags(RegisterFlags.N) && (a & 0xF) > 9))
                 correction |= 0x6;
 
-            if (!_registers.GetFlags(RegisterFlags.N))
+            if (_registers.GetFlags(RegisterFlags.C) || (!_registers.GetFlags(RegisterFlags.N) && a > 0x99))
             {
-                if ((value & 0xF) > 0x9)
-                    correction |= 6;
-                if (value > 0x99)
-                    correction |= 0x60;
-                value += correction;
-            }
-            else
-            {
-                value -= correction;
+                correction |= 0x60;
+                setFlagC = RegisterFlags.C;
             }
 
-            if (((correction << 2) & 0x100) != 0)
-                flags |= RegisterFlags.C;
-            if (_registers.A == 0)
-                flags |= RegisterFlags.Z;
+            a += _registers.GetFlags(RegisterFlags.N) ? -correction : correction;
+            a &= 0xFF;
 
-            _registers.A = (byte) (value & 0xFF);
+            var setFlagZ = a == 0 ? RegisterFlags.Z : RegisterFlags.None;
 
-            _registers.ClearFlags(RegisterFlags.Z | RegisterFlags.H | RegisterFlags.C);
-            _registers.SetFlags(flags);
+            var newFlags = (RegisterFlags) _registers.F & ~(RegisterFlags.H | RegisterFlags.Z | RegisterFlags.C);
+            newFlags |= setFlagC | setFlagZ;
+            
+            _registers.OverwriteFlags(newFlags);
+            _registers.A = (byte) a;
         }
     }
 }
diff --git a/Emux/Expressions/ExpressionParser.cs b/Emux/Expressions/ExpressionParser.cs
index 83cda79..ab93604 100644
--- a/Emux/Expressions/ExpressionParser.cs
+++ b/Emux/Expressions/ExpressionParser.cs
@@ -34,10 +34,9 @@ namespace Emux.Expressions
         public static Predicate<GameBoyCpu> CompileExpression(string code)
         {
             var lexer = new ExpressionLexer(new StringReader(code));
-            var postFix = ToPostfix(lexer).ToArray();
-
+            
             var stack = new Stack<Expression>();
-            foreach (var token in postFix)
+            foreach (var token in ToPostfix(lexer))
             {
                 switch (token.Terminal)
                 {