pkg/chip8/chip8.go

@@ -5,17 +5,17 @@ import "fmt"
 const graphicsBufferSize = 64 * 32
 
 type Chip8 struct {
-	address_register uint16
+	addressRegister uint16
-	beep_timer       uint16
+	beepTimer       uint16
-	draw_required    bool
+	drawRequired    bool
-	delay_timer      uint16
+	delayTimer      uint16
-	graphics         [graphicsBufferSize]byte
+	graphics        [graphicsBufferSize]byte
-	keys             [16]byte
+	keys            [16]byte
-	memory           [4096]byte
+	memory          [4096]byte
-	opcode           uint16
+	opcode          uint16
-	pc               uint16
+	pc              uint16
-	registers        [16]byte // an array - has a fixed length
+	registers       [16]byte // an array - has a fixed length
-	stack            []uint16 // a slice - basically a c++ vector
+	stack           []uint16 // a slice - basically a c++ vector
 }
 
 // we can't have const arrays in go
@@ -60,7 +60,7 @@ func (cpu *Chip8) GetGraphicsBuffer() [graphicsBufferSize]byte {
 func (cpu *Chip8) clearDisplay() {
 	// fuck it the gc can do the hard work for us
 	cpu.graphics = [64 * 32]byte{}
-	cpu.draw_required = true
+	cpu.drawRequired = true
 }
 
 // what if there's nothing in the stack?
@@ -153,9 +153,32 @@ func (cpu *Chip8) BitOpsAndMath() {
 		// Store lsb of reg X in reg F and then shift reg X >> 1
 		cpu.registers[0x0F] = cpu.registers[regX] & 0x01
 		cpu.registers[regX] >>= 1
+	case 7:
+		// 8XY57
+		// Set register x to X=Y-X (Set VF to 1 when there's a carry and 0 if not)
+		res := cpu.registers[regY] - cpu.registers[regX]
+		if res < 0 {
+			cpu.registers[0x0F] = 0
+		} else {
+			cpu.registers[0x0f] = 1
+		}
+		cpu.registers[regX] = res & 0xFF
 	}
 }
 
+func (cpu *Chip8) SkipIfRegistersNotEqual() {
+	x, y := (cpu.opcode>>8)&0x0F, (cpu.opcode>>4)&0x0F
+	if cpu.registers[x] != cpu.registers[y] {
+		cpu.pc += 2
+	}
+}
+
+func (cpu *Chip8) SetAddressRegister() {
+	// ANNN
+	// Sets the address register to NNN
+	cpu.addressRegister = cpu.opcode & 0x0FFF
+}
+
 func main() {
 	fmt.Printf("Hello world!\n")
 	prog := []byte{1, 2, 3, 4}

pkg/chip8/chip8_test.go

@@ -21,8 +21,8 @@ func slicesEqual(x, y []byte) bool {
 // Maybe fix
 func TestCreateCPU(t *testing.T) {
 	prog := []byte{1, 2, 3, 4}
-	new_cpu := NewCHIP8(prog)
+	newCPU := NewCHIP8(prog)
-	if !slicesEqual(new_cpu.memory[200:204], prog) {
+	if !slicesEqual(newCPU.memory[200:204], prog) {
 		t.Errorf("CPU not initalized properly")
 	}
 }
@@ -33,10 +33,10 @@ func TestClearDisplay(t *testing.T) {
 		cpu.graphics[i] = byte(i % 255)
 	}
 	cpu.clearDisplay()
-	graphics_array := cpu.GetGraphicsBuffer()
+	graphicsArray := cpu.GetGraphicsBuffer()
-	graphics_slice := graphics_array[:]
+	graphicsSlice := graphicsArray[:]
-	empty_slice := make([]byte, len(cpu.graphics))
+	emptySlice := make([]byte, len(cpu.graphics))
-	if !slicesEqual(graphics_slice, empty_slice) {
+	if !slicesEqual(graphicsSlice, emptySlice) {
 		t.Errorf("Graphics buffer not cleared properly")
 	}
 }