From a58e599c7a2971bf579dfd7a26796845ed6ad276 Mon Sep 17 00:00:00 2001
From: Kevin Hamacher <kevin.hamacher@rub.de>
Date: Thu, 2 Jun 2016 13:49:21 +0200
Subject: [PATCH] Fix DAA

---
 src/cpu.rs | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index a8e8d14..5b5ceb8 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -1083,38 +1083,39 @@ impl CPU {
                 0x26 => self.ld_r_v(REG_N_H),
                 0x27 => {
                     // Logic copied from some other emulator
-                    let mut v = self.regs[REG_A] as u16;
+                    let a = self.regs[REG_A];
 
                     if self.debug {
                         println!("DAA");
                     }
 
-                    if self.flags & FLAG_N == 0 {
-                        // Lower nibble
-                        if ((self.flags & FLAG_H) == FLAG_H) || (v & 0xF) > 9 {
-                            v += 0x06;
-                        }
+                    let mut cor: u8 = 0;
+                    if (self.flags & FLAG_H) == FLAG_H {
+                        cor |= 0x06;
+                    }
+                    if (self.flags & FLAG_C) == FLAG_C {
+                        cor |= 0x60;
+                    }
 
-                        // Higher nibble
-                        if ((self.flags & FLAG_C) == FLAG_C) || v > 0x9F {
-                            v += 0x60;
-                        }
+                    if (self.flags & FLAG_N) == FLAG_N {
+                        self.regs[REG_A] = a.wrapping_sub(cor);
                     } else {
-                        // Lower nibble
-                        if (self.flags & FLAG_H) == FLAG_H {
-                            v = v.wrapping_sub(6) & 0xFF;
+                        if (a & 0x0F) > 0x09 {
+                            cor |= 0x06;
                         }
-
-                        // Higher nibble
-                        if (self.flags & FLAG_C) == FLAG_C {
-                            v = v.wrapping_sub(0x60);
+                        if a > 0x99 {
+                            cor |= 0x60;
                         }
+                        self.regs[REG_A] = a.wrapping_add(cor);
                     }
 
                     self.clear_flag(FLAG_H);
-                    self.set_clear_flag(FLAG_C, (v & 0x100) == 0x100);
-                    self.set_clear_flag(FLAG_Z, v as u8 == 0);
-                    self.regs[REG_A] = v as u8;
+                    if cor & 0x60 == 0x60 {
+                        self.set_flag(FLAG_C);
+                    }
+
+                    let a = self.regs[REG_A];
+                    self.set_clear_flag(FLAG_Z, a == 0);
 
                     4
                 },