daa was wrong

src/instructions/misc.rs

@@ -7,36 +7,26 @@ pub fn stop(gameboy: &mut Gameboy) -> u8 {
 }
 
 pub fn daa(gameboy: &mut Gameboy) -> u8 {
-    // note: assumes a is a uint8_t and wraps from 0xff to 0
-    // if (!n_flag) {  // after an addition, adjust if (half-)carry occurred or if result is out of bounds
-    //     if (c_flag || a > 0x99) { a += 0x60; c_flag = 1; }
-    //     if (h_flag || (a & 0x0f) > 0x09) { a += 0x6; }
-    //   } else {  // after a subtraction, only adjust if (half-)carry occurred
-    //     if (c_flag) { a -= 0x60; }
-    //     if (h_flag) { a -= 0x6; }
-    //   }
-    //   // these flags are always updated
-    //   z_flag = (a == 0); // the usual z flag
-    //   h_flag = 0; // h flag is always cleared
-    let value = gameboy.cpu.registers.a;
+    let mut value = gameboy.cpu.registers.a;
     let flags = gameboy.cpu.registers.f;
     if flags.subtract {
         if flags.carry {
-            gameboy.cpu.registers.a = value.wrapping_sub(0x60);
+            value = value.wrapping_sub(0x60);
         }
         if flags.half_carry {
-            gameboy.cpu.registers.a = value.wrapping_sub(0x6);
+            value = value.wrapping_sub(0x6);
         }
     } else {
         if flags.carry || value > 0x99 {
-            gameboy.cpu.registers.a = value.wrapping_add(0x60);
+            value = value.wrapping_add(0x60);
             gameboy.cpu.registers.f.carry = true;
         }
         if flags.half_carry || (value & 0x0f) > 0x09 {
-            gameboy.cpu.registers.a = value.wrapping_add(0x6);
+            value = value.wrapping_add(0x6);
         }
     }
-    gameboy.cpu.registers.f.zero = gameboy.cpu.registers.a == 0;
+    gameboy.cpu.registers.a = value;
+    gameboy.cpu.registers.f.zero = value == 0;
     gameboy.cpu.registers.f.half_carry = false;
     const TICKS: u8 = 4;
     TICKS
@@ -49,7 +39,10 @@ mod tests {
     #[test]
     fn test_daa() {
         let mut gameboy = Gameboy::default();
-
+        gameboy.cpu.registers.a = 0x9A;
         daa(&mut gameboy);
+        assert_eq!(gameboy.cpu.registers.a, 0x00);
+        assert!(gameboy.cpu.registers.f.zero);
+        assert!(gameboy.cpu.registers.f.carry);
     }
 }