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https://github.com/mre/mos6502.git
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Add tests for stack over- and underflow
This commit is contained in:
Sam M W
parent
ad40c72dfe
commit
34bbe55712
219
src/cpu.rs
219
src/cpu.rs
@ -37,6 +37,12 @@ pub struct CPU {
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pub memory: Memory,
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}
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impl Default for CPU {
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fn default() -> Self {
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Self::new()
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}
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}
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impl CPU {
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pub fn new() -> CPU {
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CPU {
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@ -515,115 +521,125 @@ impl CPU {
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);
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}
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fn add_with_carry(&mut self, value: i8) {
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let a_before: i8 = self.registers.accumulator;
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let c_before: i8 = if self.registers.status.contains(Status::PS_CARRY) {
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1
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} else {
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0
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};
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let a_after: i8 = a_before.wrapping_add(c_before).wrapping_add(value);
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fn add_with_carry(&mut self, value: i8) {
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let a_before: i8 = self.registers.accumulator;
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let c_before: i8 = if self.registers.status.contains(Status::PS_CARRY) {
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1
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} else {
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0
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};
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let a_after: i8 = a_before.wrapping_add(c_before).wrapping_add(value);
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debug_assert_eq!(
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a_after as u8,
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a_before.wrapping_add(c_before).wrapping_add(value) as u8
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);
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debug_assert_eq!(
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a_after as u8,
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a_before.wrapping_add(c_before).wrapping_add(value) as u8
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);
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let bcd1: i8 = if (a_after & 0x0f) as u8 > 0x09 {
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0x06
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} else {
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0x00
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};
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let bcd1: i8 = if (a_after & 0x0f) as u8 > 0x09 {
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0x06
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} else {
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0x00
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};
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let bcd2: i8 = if (a_after.wrapping_add(bcd1) as u8 & 0xf0) as u8 > 0x90 {
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0x60
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} else {
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0x00
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};
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let bcd2: i8 = if (a_after.wrapping_add(bcd1) as u8 & 0xf0) as u8 > 0x90 {
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0x60
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} else {
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0x00
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};
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let result: i8 = if self.registers.status.contains(Status::PS_DECIMAL_MODE) {
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a_after.wrapping_add(bcd1).wrapping_add(bcd2)
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} else {
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a_after
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};
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let result: i8 = if self.registers.status.contains(Status::PS_DECIMAL_MODE) {
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a_after.wrapping_add(bcd1).wrapping_add(bcd2)
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} else {
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a_after
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};
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let did_carry = (result as u8) < (a_before as u8);
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let did_carry = (result as u8) < (a_before as u8);
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let did_overflow = (a_before < 0 && value < 0 && a_after >= 0)
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|| (a_before > 0 && value > 0 && a_after <= 0);
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let did_overflow = (a_before < 0 && value < 0 && a_after >= 0)
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|| (a_before > 0 && value > 0 && a_after <= 0);
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let mask = Status::PS_CARRY | Status::PS_OVERFLOW;
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let mask = Status::PS_CARRY | Status::PS_OVERFLOW;
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self.registers.status.set_with_mask( mask, Status::new(StatusArgs { carry: did_carry, overflow: did_overflow, ..StatusArgs::none() }),);
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self.registers.status.set_with_mask(
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mask,
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Status::new(StatusArgs {
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carry: did_carry,
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overflow: did_overflow,
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..StatusArgs::none()
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}),
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);
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self.load_accumulator(result);
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self.load_accumulator(result);
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debug!("accumulator: {}", self.registers.accumulator);
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}
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debug!("accumulator: {}", self.registers.accumulator);
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}
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fn and(&mut self, value: i8) {
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let a_after = self.registers.accumulator & value;
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self.load_accumulator(a_after);
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}
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fn subtract_with_carry(&mut self, value: i8) {
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// A - M - (1 - C)
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fn subtract_with_carry(&mut self, value: i8) {
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// A - M - (1 - C)
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// nc -- 'not carry'
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let nc: i8 = if self.registers.status.contains(Status::PS_CARRY) {
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0
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} else {
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1
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};
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// nc -- 'not carry'
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let nc: i8 = if self.registers.status.contains(Status::PS_CARRY) {
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0
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} else {
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1
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};
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let a_before: i8 = self.registers.accumulator;
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let a_before: i8 = self.registers.accumulator;
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let a_after = a_before.wrapping_sub(value).wrapping_sub(nc);
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let a_after = a_before.wrapping_sub(value).wrapping_sub(nc);
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// The overflow flag is set on two's-complement overflow.
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//
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// range of A is -128 to 127
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// range of - M - (1 - C) is -128 to 128
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// -(127 + 1) to -(-128 + 0)
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//
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let over =
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((nc == 0 && value < 0) || (nc == 1 && value < -1)) && a_before >= 0 && a_after < 0;
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// The overflow flag is set on two's-complement overflow.
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//
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// range of A is -128 to 127
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// range of - M - (1 - C) is -128 to 128
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// -(127 + 1) to -(-128 + 0)
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//
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let over =
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((nc == 0 && value < 0) || (nc == 1 && value < -1)) && a_before >= 0 && a_after < 0;
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let under = (a_before < 0) && (-value - nc < 0) && a_after >= 0;
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let under = (a_before < 0) && (-value - nc < 0) && a_after >= 0;
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let did_overflow = over || under;
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let did_overflow = over || under;
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let mask = Status::PS_CARRY | Status::PS_OVERFLOW;
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let mask = Status::PS_CARRY | Status::PS_OVERFLOW;
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let bcd1: i8 = if (a_before & 0x0f).wrapping_sub(nc) < (value & 0x0f) {
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0x06
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} else {
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0x00
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};
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let bcd1: i8 = if (a_before & 0x0f).wrapping_sub(nc) < (value & 0x0f) {
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0x06
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} else {
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0x00
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};
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let bcd2: i8 = if (a_after.wrapping_sub(bcd1) as u8 & 0xf0) as u8 > 0x90 {
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0x60
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} else {
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0x00
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};
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let result: i8 = if self.registers.status.contains(Status::PS_DECIMAL_MODE) {
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a_after.wrapping_sub(bcd1).wrapping_sub(bcd2)
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} else {
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a_after
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};
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let bcd2: i8 = if (a_after.wrapping_sub(bcd1) as u8 & 0xf0) as u8 > 0x90 {
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0x60
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} else {
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0x00
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};
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// The carry flag is set on unsigned overflow.
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let did_carry = (result as u8) > (a_before as u8);
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let result: i8 = if self.registers.status.contains(Status::PS_DECIMAL_MODE) {
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a_after.wrapping_sub(bcd1).wrapping_sub(bcd2)
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} else {
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a_after
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};
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self.registers.status.set_with_mask(
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mask,
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Status::new(StatusArgs { carry: did_carry, overflow: did_overflow, ..StatusArgs::none() }),
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);
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// The carry flag is set on unsigned overflow.
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let did_carry = (result as u8) > (a_before as u8);
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self.registers.status.set_with_mask(
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mask,
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Status::new(StatusArgs {
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carry: did_carry,
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overflow: did_overflow,
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..StatusArgs::none()
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}),
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);
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self.load_accumulator(result);
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}
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self.load_accumulator(result);
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}
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fn decrement_memory(&mut self, addr: Address) {
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let value_new = self.memory.get_byte(addr).wrapping_sub(1);
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@ -779,51 +795,54 @@ mod tests {
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use super::*;
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use num::range_inclusive;
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#[test]
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fn decimal_add_test() {
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let mut cpu = CPU::new();
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cpu.registers.status.or(Status::PS_DECIMAL_MODE);
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cpu.add_with_carry(0x09);
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#[test]
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fn decimal_add_test() {
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let mut cpu = CPU::new();
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cpu.registers.status.or(Status::PS_DECIMAL_MODE);
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cpu.add_with_carry(0x09);
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assert_eq!(cpu.registers.accumulator, 0x09);
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assert_eq!(cpu.registers.status.contains(Status::PS_CARRY), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_ZERO), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_NEGATIVE), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_OVERFLOW), false);
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cpu.add_with_carry(0x43);
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cpu.add_with_carry(0x43);
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assert_eq!(cpu.registers.accumulator, 0x52);
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assert_eq!(cpu.registers.status.contains(Status::PS_CARRY), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_ZERO), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_NEGATIVE), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_OVERFLOW), false);
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cpu.add_with_carry(0x48);
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cpu.add_with_carry(0x48);
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assert_eq!(cpu.registers.accumulator, 0x00);
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assert_eq!(cpu.registers.status.contains(Status::PS_CARRY), true);
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assert_eq!(cpu.registers.status.contains(Status::PS_ZERO), true);
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assert_eq!(cpu.registers.status.contains(Status::PS_NEGATIVE), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_OVERFLOW), true);
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}
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}
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#[test]
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fn decimal_subtract_test() {
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let mut cpu = CPU::new();
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cpu.registers.status.or(Status::PS_DECIMAL_MODE);
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cpu.subtract_with_carry(0x48);
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#[test]
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fn decimal_subtract_test() {
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let mut cpu = CPU::new();
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cpu.registers
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.status
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.or(Status::PS_DECIMAL_MODE | Status::PS_CARRY);
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cpu.registers.accumulator = 0;
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cpu.subtract_with_carry(0x48);
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assert_eq!(cpu.registers.accumulator as u8, 0x52);
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assert_eq!(cpu.registers.status.contains(Status::PS_CARRY), true);
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assert_eq!(cpu.registers.status.contains(Status::PS_ZERO), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_NEGATIVE), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_OVERFLOW), false);
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cpu.subtract_with_carry(0x43);
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cpu.subtract_with_carry(0x43);
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assert_eq!(cpu.registers.status.contains(Status::PS_CARRY), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_ZERO), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_NEGATIVE), false);
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assert_eq!(cpu.registers.status.contains(Status::PS_OVERFLOW), false);
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}
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}
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#[test]
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fn add_with_carry_test() {
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@ -1342,5 +1361,11 @@ mod tests {
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}
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}
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}
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}
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#[test]
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fn stack_underflow() {
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let mut cpu = CPU::new();
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let _val: u8 = cpu.pull_from_stack();
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}
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}
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