go/chip8-emulator
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SUBN + refactor

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This commit is contained in:
Jairinho 2022-02-24 16:14:05 -03:00
parent 3d4e91aa40
commit b10d6e6c81
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GPG Key ID: 954589B18A21D5B6
2 changed files with 21 additions and 13 deletions
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21
chip8/chip8.go
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@ -28,12 +28,10 @@ type Emulator struct {
I uint16 // address register
SP uint16 // stack pointer
PC uint16 // program counter
DT uint8 // delay timer
ST uint8 // sound timer
Memory [MemorySize]uint8 // 4KB of system RAM
Timer struct {
Delay uint8 // delay timer
Sound uint8 // sound timer
}
ROM []uint8
ROM []uint8 // game rom
}
func NewEmulator() *Emulator {
@ -47,17 +45,17 @@ func (emulator *Emulator) Reset() {
emulator.I = 0
emulator.SP = StackAddress
emulator.PC = ProgramAddress
emulator.DT = 0
emulator.ST = 0
emulator.Memory = [MemorySize]uint8{}
emulator.Timer.Delay = 0
emulator.Timer.Sound = 0
copy(emulator.Memory[ProgramAddress:], emulator.ROM)
}
func (emulator *Emulator) Cycle() {
pc := emulator.PC
emulator.Timer.Delay = uint8(math.Max(0, float64(emulator.Timer.Delay)-1))
emulator.Timer.Sound = uint8(math.Max(0, float64(emulator.Timer.Sound)-1))
emulator.DT = uint8(math.Max(0, float64(emulator.DT)-1))
emulator.ST = uint8(math.Max(0, float64(emulator.ST)-1))
instruction := binary.BigEndian.Uint16(emulator.Memory[emulator.PC:])
@ -85,7 +83,7 @@ func (emulator *Emulator) Cycle() {
case 0x8:
switch instruction & 0x000F {
case 0x0: // 8xy0 - LD Vx, Vy
emulator.LoadRegister(x, y)
emulator.Load(x, y)
case 0x1: // 8xy1 - OR Vx, Vy
emulator.Or(x, y)
case 0x2: // 8xy2 - AND Vx, Vy
@ -93,12 +91,13 @@ func (emulator *Emulator) Cycle() {
case 0x3: // 8xy3 - XOR Vx, Vy
emulator.Xor(x, y)
case 0x4: // 8xy4 - ADD Vx, Vy
emulator.AddRegisters(x, y)
emulator.Add(x, y)
case 0x5: // 8xy5 - SUB Vx, Vy
emulator.Sub(x, y)
case 0x6: // 8xy6 - SHR Vx {, Vy}
emulator.ShiftRight(x)
case 0x7: // 8xy7 - SUBN Vx, Vy
emulator.SubN(x, y)
case 0xE: // 8xyE - SHL Vx {, Vy}
emulator.ShiftLeft(x)
}

13
chip8/instructions.go
View File

@ -71,7 +71,7 @@ func (emulator *Emulator) AddByte(x uint8, kk uint8) {
// Set Vx = Vy.
//
// Stores the value of register Vy in register Vx.
func (emulator *Emulator) LoadRegister(x uint8, y uint8) {
func (emulator *Emulator) Load(x uint8, y uint8) {
emulator.V[x] = emulator.V[y]
}
@ -107,7 +107,7 @@ func (emulator *Emulator) Xor(x uint8, y uint8) {
// The values of Vx and Vy are added together.
// If the result is greater than 8 bits (i.e., > 255,) VF is set to 1,
// otherwise 0. Only the lowest 8 bits of the result are kept, and stored in Vx.
func (emulator *Emulator) AddRegisters(x uint8, y uint8) {
func (emulator *Emulator) Add(x uint8, y uint8) {
sum := uint16(emulator.V[x]) + uint16(emulator.V[y])
emulator.V[x] = uint8(sum)
emulator.V[0xF] = uint8(sum >> 8)
@ -132,6 +132,15 @@ func (emulator *Emulator) ShiftRight(x uint8) {
emulator.V[x] >>= 1
}
// Set Vx = Vy - Vx, set VF = NOT borrow.
//
// If Vy > Vx, then VF is set to 1, otherwise 0.
// Then Vx is subtracted from Vy, and the results stored in Vx.
func (emulator *Emulator) SubN(x uint8, y uint8) {
emulator.V[0xF] = map[bool]uint8{true: 1, false: 0}[emulator.V[y] > emulator.V[x]]
emulator.V[x] = emulator.V[y] - emulator.V[x]
}
// Set Vx = Vx SHL 1.
//
// If the most-significant bit of Vx is 1, then VF is set to 1, otherwise to 0.