diff --git a/src/cpu.rs b/src/cpu.rs index d3a79c8..19125f6 100644 --- a/src/cpu.rs +++ b/src/cpu.rs @@ -227,15 +227,15 @@ impl CPU { // | 2aaa | Pushes pc onto the stack, then jumps to a 0x2 => self.call(a, bus), // | 3xbb | Skips next instruction if register X == b - 0x3 => self.skip_if_x_equal_byte(x, b), + 0x3 => self.skip_equals_immediate(x, b), // | 4xbb | Skips next instruction if register X != b - 0x4 => self.skip_if_x_not_equal_byte(x, b), + 0x4 => self.skip_not_equals_immediate(x, b), // # Performs a register-register comparison // |opcode| effect | // |------|------------------------------------| // | 9XY0 | Skip next instruction if vX == vY | 0x5 => match n { - 0x0 => self.skip_if_x_equal_y(x, y), + 0x0 => self.skip_equals(x, y), _ => self.unimplemented(opcode), }, // 6xbb: Loads immediate byte b into register vX @@ -255,15 +255,15 @@ impl CPU { // | 8xy7 | X = Y - X; Set vF=carry | // | 8xyE | X = X << 1 | 0x8 => match n { - 0x0 => self.load_y_into_x(x, y), - 0x1 => self.x_orequals_y(x, y), - 0x2 => self.x_andequals_y(x, y), - 0x3 => self.x_xorequals_y(x, y), - 0x4 => self.x_addequals_y(x, y), - 0x5 => self.x_subequals_y(x, y), - 0x6 => self.shift_right_x(x), - 0x7 => self.backwards_subtract(x, y), - 0xE => self.shift_left_x(x), + 0x0 => self.load(x, y), + 0x1 => self.or(x, y), + 0x2 => self.and(x, y), + 0x3 => self.xor(x, y), + 0x4 => self.add(x, y), + 0x5 => self.sub(x, y), + 0x6 => self.shift_right(x, y), + 0x7 => self.backwards_sub(x, y), + 0xE => self.shift_left(x, y), _ => self.unimplemented(opcode), }, // # Performs a register-register comparison @@ -271,11 +271,11 @@ impl CPU { // |------|------------------------------------| // | 9XY0 | Skip next instruction if vX != vY | 0x9 => match n { - 0 => self.skip_if_x_not_equal_y(x, y), + 0 => self.skip_not_equals(x, y), _ => self.unimplemented(opcode), }, // Aaaa: Load address #a into register I - 0xa => self.load_indirect_register(a), + 0xa => self.load_i_immediate(a), // Baaa: Jump to &adr + v0 0xb => self.jump_indexed(a), // Cxbb: Stores a random number + the provided byte into vX @@ -286,11 +286,11 @@ impl CPU { // # Skips instruction on value of keypress // |opcode| effect | // |------|------------------------------------| - // | eX9e | Skip next instruction if key == #X | - // | eXa1 | Skip next instruction if key != #X | + // | eX9e | Skip next instruction if key == vX | + // | eXa1 | Skip next instruction if key != vX | 0xe => match b { - 0x9e => self.skip_if_key_equals_x(x), - 0xa1 => self.skip_if_key_not_x(x), + 0x9e => self.skip_key_equals(x), + 0xa1 => self.skip_key_not_equals(x), _ => self.unimplemented(opcode), }, @@ -307,15 +307,15 @@ impl CPU { // | fX55 | DMA Stor from I to registers 0..X | // | fX65 | DMA Load from I to registers 0..X | 0xf => match b { - 0x07 => self.get_delay_timer(x), + 0x07 => self.load_delay_timer(x), 0x0A => self.wait_for_key(x), - 0x15 => self.load_delay_timer(x), - 0x18 => self.load_sound_timer(x), - 0x1E => self.add_to_indirect(x), - 0x29 => self.load_sprite_x(x), - 0x33 => self.bcd_convert_i(x, bus), - 0x55 => self.dma_store(x, bus), - 0x65 => self.dma_load(x, bus), + 0x15 => self.store_delay_timer(x), + 0x18 => self.store_sound_timer(x), + 0x1E => self.add_i(x), + 0x29 => self.load_sprite(x), + 0x33 => self.bcd_convert(x, bus), + 0x55 => self.store_dma(x, bus), + 0x65 => self.load_dma(x, bus), _ => self.unimplemented(opcode), }, _ => unimplemented!("Extracted nibble from byte, got >nibble?"), @@ -398,6 +398,9 @@ impl Default for CPU { } } +// Below this point, comments may be duplicated per impl' block, +// since some opcodes handle multiple instructions. + // | 0aaa | Issues a "System call" (ML routine) // // |opcode| effect | @@ -460,7 +463,7 @@ impl CPU { impl CPU { /// 3xbb: Skips the next instruction if register X == b #[inline] - fn skip_if_x_equal_byte(&mut self, x: Reg, b: u8) { + fn skip_equals_immediate(&mut self, x: Reg, b: u8) { if self.v[x] == b { self.pc = self.pc.wrapping_add(2); } @@ -471,7 +474,7 @@ impl CPU { impl CPU { /// 4xbb: Skips the next instruction if register X != b #[inline] - fn skip_if_x_not_equal_byte(&mut self, x: Reg, b: u8) { + fn skip_not_equals_immediate(&mut self, x: Reg, b: u8) { if self.v[x] != b { self.pc = self.pc.wrapping_add(2); } @@ -486,7 +489,7 @@ impl CPU { impl CPU { /// 5xy0: Skips the next instruction if register X != register Y #[inline] - fn skip_if_x_equal_y(&mut self, x: Reg, y: Reg) { + fn skip_equals(&mut self, x: Reg, y: Reg) { if self.v[x] == self.v[y] { self.pc = self.pc.wrapping_add(2); } @@ -526,32 +529,44 @@ impl CPU { // | 8xyE | X = X << 1 | impl CPU { /// 8xy0: Loads the value of y into x + /// + /// # Authenticity + /// The original chip-8 interpreter will clobber vF for any 8-series instruction #[inline] - fn load_y_into_x(&mut self, x: Reg, y: Reg) { + fn load(&mut self, x: Reg, y: Reg) { self.v[x] = self.v[y]; if self.flags.authentic { self.v[0xf] = 0; } } /// 8xy1: Performs bitwise or of vX and vY, and stores the result in vX + /// + /// # Authenticity + /// The original chip-8 interpreter will clobber vF for any 8-series instruction #[inline] - fn x_orequals_y(&mut self, x: Reg, y: Reg) { + fn or(&mut self, x: Reg, y: Reg) { self.v[x] |= self.v[y]; if self.flags.authentic { self.v[0xf] = 0; } } /// 8xy2: Performs bitwise and of vX and vY, and stores the result in vX + /// + /// # Authenticity + /// The original chip-8 interpreter will clobber vF for any 8-series instruction #[inline] - fn x_andequals_y(&mut self, x: Reg, y: Reg) { + fn and(&mut self, x: Reg, y: Reg) { self.v[x] &= self.v[y]; if self.flags.authentic { self.v[0xf] = 0; } } /// 8xy3: Performs bitwise xor of vX and vY, and stores the result in vX + /// + /// # Authenticity + /// The original chip-8 interpreter will clobber vF for any 8-series instruction #[inline] - fn x_xorequals_y(&mut self, x: Reg, y: Reg) { + fn xor(&mut self, x: Reg, y: Reg) { self.v[x] ^= self.v[y]; if self.flags.authentic { self.v[0xf] = 0; @@ -559,37 +574,47 @@ impl CPU { } /// 8xy4: Performs addition of vX and vY, and stores the result in vX #[inline] - fn x_addequals_y(&mut self, x: Reg, y: Reg) { + fn add(&mut self, x: Reg, y: Reg) { let carry; (self.v[x], carry) = self.v[x].overflowing_add(self.v[y]); self.v[0xf] = carry.into(); } /// 8xy5: Performs subtraction of vX and vY, and stores the result in vX #[inline] - fn x_subequals_y(&mut self, x: Reg, y: Reg) { + fn sub(&mut self, x: Reg, y: Reg) { let carry; (self.v[x], carry) = self.v[x].overflowing_sub(self.v[y]); self.v[0xf] = (!carry).into(); } /// 8xy6: Performs bitwise right shift of vX + /// + /// # Authenticity + /// On the original chip-8 interpreter, this would perform the operation on vY + /// and store the result in vX. This behavior was left out, for now. #[inline] - fn shift_right_x(&mut self, x: Reg) { - let shift_out = self.v[x] & 1; - self.v[x] >>= 1; + fn shift_right(&mut self, x: Reg, y: Reg) { + let src: Reg = if self.flags.authentic {y} else {x}; + let shift_out = self.v[src] & 1; + self.v[x] = self.v[src] >> 1; self.v[0xf] = shift_out; } /// 8xy7: Performs subtraction of vY and vX, and stores the result in vX #[inline] - fn backwards_subtract(&mut self, x: Reg, y: Reg) { + fn backwards_sub(&mut self, x: Reg, y: Reg) { let carry; (self.v[x], carry) = self.v[y].overflowing_sub(self.v[x]); self.v[0xf] = (!carry).into(); } /// 8X_E: Performs bitwise left shift of vX + /// + /// # Authenticity + /// On the original chip-8 interpreter, this would perform the operation on vY + /// and store the result in vX. This behavior was left out, for now. #[inline] - fn shift_left_x(&mut self, x: Reg) { - let shift_out: u8 = self.v[x] >> 7; - self.v[x] <<= 1; + fn shift_left(&mut self, x: Reg, y: Reg) { + let src: Reg = if self.flags.authentic {y} else {x}; + let shift_out: u8 = self.v[src] >> 7; + self.v[x] = self.v[src] << 1; self.v[0xf] = shift_out; } } @@ -602,7 +627,7 @@ impl CPU { impl CPU { /// 9xy0: Skip next instruction if X != y #[inline] - fn skip_if_x_not_equal_y(&mut self, x: Reg, y: Reg) { + fn skip_not_equals(&mut self, x: Reg, y: Reg) { if self.v[x] != self.v[y] { self.pc = self.pc.wrapping_add(2); } @@ -613,7 +638,7 @@ impl CPU { impl CPU { /// Aadr: Load address #adr into register I #[inline] - fn load_indirect_register(&mut self, a: Adr) { + fn load_i_immediate(&mut self, a: Adr) { self.i = a; } } @@ -675,7 +700,7 @@ impl CPU { impl CPU { /// Ex9E: Skip next instruction if key == #X #[inline] - fn skip_if_key_equals_x(&mut self, x: Reg) { + fn skip_key_equals(&mut self, x: Reg) { let x = self.v[x] as usize; if self.keys[x] { self.pc += 2; @@ -683,7 +708,7 @@ impl CPU { } /// ExaE: Skip next instruction if key != #X #[inline] - fn skip_if_key_not_x(&mut self, x: Reg) { + fn skip_key_not_equals(&mut self, x: Reg) { let x = self.v[x] as usize; if !self.keys[x] { self.pc += 2; @@ -710,7 +735,7 @@ impl CPU { /// vX = DT /// ``` #[inline] - fn get_delay_timer(&mut self, x: Reg) { + fn load_delay_timer(&mut self, x: Reg) { self.v[x] = self.delay; } /// Fx0A: Wait for key, then vX = K @@ -733,7 +758,7 @@ impl CPU { /// DT = vX /// ``` #[inline] - fn load_delay_timer(&mut self, x: Reg) { + fn store_delay_timer(&mut self, x: Reg) { self.delay = self.v[x]; } /// Fx18: Load vX into ST @@ -741,7 +766,7 @@ impl CPU { /// ST = vX; /// ``` #[inline] - fn load_sound_timer(&mut self, x: Reg) { + fn store_sound_timer(&mut self, x: Reg) { self.sound = self.v[x]; } /// Fx1e: Add vX to I, @@ -749,7 +774,7 @@ impl CPU { /// I += vX; /// ``` #[inline] - fn add_to_indirect(&mut self, x: Reg) { + fn add_i(&mut self, x: Reg) { self.i += self.v[x] as u16; } /// Fx29: Load sprite for character x into I @@ -757,20 +782,24 @@ impl CPU { /// I = sprite(X); /// ``` #[inline] - fn load_sprite_x(&mut self, x: Reg) { + fn load_sprite(&mut self, x: Reg) { self.i = self.font + (5 * (self.v[x] as Adr % 0x10)); } /// Fx33: BCD convert X into I`[0..3]` #[inline] - fn bcd_convert_i(&mut self, x: Reg, bus: &mut Bus) { + fn bcd_convert(&mut self, x: Reg, bus: &mut Bus) { let x = self.v[x]; bus.write(self.i.wrapping_add(2), x % 10); bus.write(self.i.wrapping_add(1), x / 10 % 10); bus.write(self.i, x / 100 % 10); } /// Fx55: DMA Stor from I to registers 0..X + /// + /// # Authenticity + /// The original chip-8 interpreter uses I to directly index memory, + /// with the side effect of leaving I as I+X+1 after the transfer is done. #[inline] - fn dma_store(&mut self, x: Reg, bus: &mut Bus) { + fn store_dma(&mut self, x: Reg, bus: &mut Bus) { let i = self.i as usize; for (reg, value) in bus .get_mut(i..=i + x) @@ -785,8 +814,12 @@ impl CPU { } } /// Fx65: DMA Load from I to registers 0..X + /// + /// # Authenticity + /// The original chip-8 interpreter uses I to directly index memory, + /// with the side effect of leaving I as I+X+1 after the transfer is done. #[inline] - fn dma_load(&mut self, x: Reg, bus: &mut Bus) { + fn load_dma(&mut self, x: Reg, bus: &mut Bus) { let i = self.i as usize; for (reg, value) in bus .get(i + 0..=i + x)