Write dec B and update flags

sdslabs · Jan 21, 2023 · c4dab4b · c4dab4b
1 parent 3042c51
commit c4dab4b
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Showing 2 changed files with 38 additions and 6 deletions.
diff --git a/src/cpu.cpp b/src/cpu.cpp
@@ -58,9 +58,41 @@ int CPU::LD_BC_A()
 	return 8;
 }
 
-int CPU::INC_BC() { return 0; }
+int CPU::INC_BC()
+{
+	reg_BC.dat += 1;
+    reg_PC.dat += 1;
+    printf("INC BC\n");
+    return 8;
+}
 int CPU::INC_B() { return 0; }
-int CPU::DEC_B() { return 0; }
+int CPU::DEC_B()
+{
+	reg_BC.hi -= 1;
+	if (reg_BC.hi == 0)
+	{
+        reg_AF.lo |= FLAG_ZERO_z;
+    }
+    else
+    {
+        reg_AF.lo &= ~FLAG_ZERO_z;
+    }
+
+	reg_AF.lo |= FLAG_SUBTRACT_n;
+
+	if (reg_BC.hi == 0xFF)
+	{
+		reg_AF.lo |= FLAG_HALF_CARRY_h;
+    }
+    else
+    {
+        reg_AF.lo &= ~FLAG_HALF_CARRY_h;
+    }
+
+    reg_PC.dat += 1;
+    printf("DEC B\n");
+    return 4;
+}
 int CPU::LD_B_u8() { return 0; }
 int CPU::RLCA() { return 0; }
 int CPU::LD_u16_SP() { return 0; }

diff --git a/src/cpu.h b/src/cpu.h
@@ -44,10 +44,10 @@ class CPU
 	// Bit 0-3 are not used
 	enum Flags
 	{
-		FLAG_CARRY_c = 4,
-		FLAG_HALF_CARRY_h = 5,
-		FLAG_SUBTRACT_n = 6,
-		FLAG_ZERO_z = 7
+		FLAG_CARRY_c = 0x10,
+		FLAG_HALF_CARRY_h = 0x20,
+		FLAG_SUBTRACT_n = 0x40,
+		FLAG_ZERO_z = 0x80
 	};
 
 	// Memory Map