Implement SBC fully, and finalize ADC/SBC

Both main arithmetic operations are now complete. Before turning in for the day, going to try to test/implement the rest of the basic arithmatic operations so I can finally hit v0.1.1. IT ONLY TOOK A YEAR. SBC also has the same hold on decimal mode, going to add a note about SBC on Issue #1.
Spalynx · Nov 19, 2018 · ffdc6ce · ffdc6ce
1 parent e9aa613
commit ffdc6ce
Show file tree

Hide file tree

Showing 3 changed files with 43 additions and 10 deletions.
diff --git a/doc/NES_TODO.org b/doc/NES_TODO.org
@@ -30,7 +30,7 @@ CLOSED: [2018-11-18 Sun 12:37]
 CLOSED: [2018-11-18 Sun 12:38]
 - State "DONE"       from "TODO"       [2018-11-18 Sun 12:38]
 **** DONE testOP_LDY()
-** TODO [20%] v0.1.1 : "Primary Arithmetic Operations"
+** TODO [40%] v0.1.1 : "Primary Arithmetic Operations"
 *** DONE ADC : "Add with Carry"
 CLOSED: [2018-11-19 Mon 09:59]
 - State "DONE"       from "TODO"       [2018-11-19 Mon 09:59]
@@ -47,10 +47,19 @@ CLOCK: [2018-11-18 Sun 10:51]--[2018-11-18 Sun 12:06] =>  1:15
 CLOSED: [2018-11-19 Mon 09:58]
 - State "WAIT"       from              [2018-11-19 Mon 09:58] \\
   See documentation on issue #1, or src/core/cpu_test.rs::testOP_ADC_decimal().
-*** TODO SBC : "Subtract with Borrow"
-**** TODO testOP_SBC()
-**** TODO testOP_SBC_signed()
-**** TODO testOP_SBC_decimal()
+*** DONE SBC : "Subtract with Borrow"
+CLOSED: [2018-11-19 Mon 11:39]
+- State "DONE"       from "TODO"       [2018-11-19 Mon 11:39]
+**** DONE testOP_SBC()
+CLOSED: [2018-11-19 Mon 11:38]
+- State "DONE"       from "TODO"       [2018-11-19 Mon 11:38]
+**** DONE testOP_SBC_signed()
+CLOSED: [2018-11-19 Mon 11:38]
+- State "DONE"       from "TODO"       [2018-11-19 Mon 11:38]
+**** WAIT testOP_SBC_decimal()
+CLOSED: [2018-11-19 Mon 11:38]
+- State "WAIT"       from              [2018-11-19 Mon 11:38] \\
+  Same as [[testOP_ADC_decimal()]]...
 *** TODO AND : "Bitwise AND with Accumulator"
 **** TODO testOP_AND()
 *** TODO EOR : "Bitwise Exclusive OR with Accumulator"

diff --git a/src/core/cpu.rs b/src/core/cpu.rs
@@ -214,8 +214,8 @@ impl CPU {
     //#! Flag OPCODES.
     //   Why not set_status_old()? Simply: Not fast enough.
     //   Wondering if I should make /fake/ OPs for other flags.
-    /// CLC - Clear Carry. Sets carry to false.
 
+    /// CLC - Clear Carry. Sets carry to false.
     pub fn CLC(&mut self) {     self.status = self.status ^ (1);}
     /// CLD - Clear Decimal. Sets decimal to false.
     pub fn CLD(&mut self) {     self.status = self.status ^ (1 << 3);   }
@@ -281,7 +281,15 @@ impl CPU {
 
     /// SBC
     /// Subtract with borrow.
-    pub fn SBC(&self) {}
+    /// This function implements all of ADC functionality by simply negating the
+    ///  value of the operand.
+    /// NOTE: Without carry being added, the sent value is off-by-one. Supposedly
+    ///       it is common practice to call SEC() prior to SBC(val).
+    pub fn SBC <AM: AddressingMode>(&mut self, am: AM){
+        let b: u8 = am.load(self) as u8;
+
+        self.ADC(ImmediateAM{address: b^0xFF});
+    }
 
     /// AND
     /// Bitwise AND with accumulator, takes memory address as parameter,

diff --git a/src/core/cpu_test.rs b/src/core/cpu_test.rs
@@ -339,7 +339,6 @@ pub mod cpu_test {
 
     #[test]
     fn testOP_ADC_signed (){
-        //Testing signed arithmetic.
         let mut test_cpu = super::CPU::new();
 
         test_cpu.LDA(ImmediateAM{address: 0b01111111u8}); //+127
@@ -376,14 +375,31 @@ pub mod cpu_test {
     }
     #[test]
     fn testOP_SBC() {
-        assert!(false);
+        let mut cpu = super::CPU::new();
+
+        cpu.SEC(); //C is set in subtraction.
+        cpu.memory.set(0x755, 237); 
+        cpu.LDA(AbsoluteAM{address:  0x755}); //Filling register a with first value.
+        cpu.SBC(ImmediateAM{address: 20});   //Subtracting second value to A.
+
+        assert_eq!(cpu.a, 217);
     }
     #[test]
     fn testOP_SBC_signed() {
-        assert!(false);
+        let mut cpu = super::CPU::new();
+
+        cpu.SEC(); //C is set in subtraction.
+        cpu.LDA(ImmediateAM{address: 0b00000001u8}); //+1
+        cpu.SBC(ImmediateAM{address: 0b00000010u8}); //+2
+
+        //Tests of this addition:
+        assert_eq!(cpu.a, 0b11111111u8); // = -1 (254)
+        assert_eq!(cpu.get_status("C"), false, "SBC-Signed-Borrow Required"); 
     }
     #[test]
     fn testOP_SBC_decimal() {
+        ///Same hold as testOP_ADC_decimal()...
+        /// Task state on WAIT.
         assert!(false);
     }
     #[test]