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Implements ADC and SBC.

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This commit is contained in:
Thomas Harte 2021-01-21 18:53:24 -05:00
parent 04024ca159
commit c10c161d39
1 changed files with 63 additions and 2 deletions
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65
InstructionSets/M50740/Executor.cpp
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@ -350,7 +350,6 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
// TODO:
//
// BRK, STP
// ADC, SBC
case Operation::ASL:
carry_flag_ = *operand >> 7;
@ -408,6 +407,7 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
#undef op_eor
#undef op_and
#undef op_ora
#undef index
#define op_cmp(x) { \
const uint16_t temp16 = x - *operand; \
@ -425,7 +425,68 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
case Operation::CPY: op_cmp(y_); break;
#undef op_cmp
#undef index
case Operation::SBC:
case Operation::ADC: {
const uint8_t a = index_mode_ ? read(x_) : a_;
if(decimal_mode_) {
if(operation == Operation::ADC) {
uint16_t partials = 0;
int result = carry_flag_;
#define nibble(mask, limit, adjustment, carry) \
result += (a & mask) + (*operand & mask); \
partials += result & mask; \
if(result >= limit) result = ((result + (adjustment)) & (carry - 1)) + carry;
nibble(0x000f, 0x000a, 0x0006, 0x00010);
nibble(0x00f0, 0x00a0, 0x0060, 0x00100);
#undef nibble
overflow_result_ = uint8_t((partials ^ a) & (partials ^ *operand));
set_nz(uint8_t(result));
carry_flag_ = (result >> 8) & 1;
} else {
unsigned int result = 0;
unsigned int borrow = carry_flag_ ^ 1;
const uint16_t decimal_result = uint16_t(a - *operand - borrow);
#define nibble(mask, adjustment, carry) \
result += (a & mask) - (*operand & mask) - borrow; \
if(result > mask) result -= adjustment; \
borrow = (result > mask) ? carry : 0; \
result &= (carry - 1);
nibble(0x000f, 0x0006, 0x00010);
nibble(0x00f0, 0x0060, 0x00100);
#undef nibble
overflow_result_ = uint8_t((decimal_result ^ a) & (~decimal_result ^ *operand));
set_nz(uint8_t(result));
carry_flag_ = ((borrow >> 8)&1)^1;
}
} else {
int result;
if(operation == Operation::ADC) {
result = int(a + *operand + carry_flag_);
overflow_result_ = uint8_t((result ^ a) & (result ^ *operand));
} else {
result = int(a + ~*operand + carry_flag_);
overflow_result_ = uint8_t((result ^ a) & (result ^ ~*operand));
}
set_nz(uint8_t(result));
carry_flag_ = (result >> 8) & 1;
}
if(index_mode_) {
write(x_, a);
} else {
a_ = a;
}
} break;
/*
Already removed from the instruction stream: