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Tidy arithmetic overflow handling in M6502 core

This commit is contained in:
Adrian Conlon 2024-01-07 14:35:12 +00:00
parent 4f4bc5355d
commit 86ef340650
2 changed files with 11 additions and 3 deletions
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8
M6502/inc/mos6502.h
View File

@ -145,6 +145,14 @@ namespace EightBit {
adjustNegative(datum);
}
constexpr void adjustOverflow_add(uint8_t operand, uint8_t data, uint8_t intermediate) noexcept {
set_flag(VF, negative(~(operand ^ data) & (operand ^ intermediate)));
}
constexpr void adjustOverflow_subtract(uint8_t operand, uint8_t data, uint8_t intermediate) noexcept {
set_flag(VF, negative((operand ^ data) & (operand ^ intermediate)));
}
// Miscellaneous
void branch(int condition) noexcept;

6
M6502/src/mos6502.cpp
View File

@ -549,7 +549,7 @@ uint8_t EightBit::MOS6502::sbc(const uint8_t operand, const uint8_t data) noexce
const auto difference = m_intermediate;
adjustNZ(difference.low);
set_flag(VF, negative((operand ^ data) & (operand ^ difference.low)));
adjustOverflow_subtract(operand, data, difference.low);
reset_flag(CF, difference.high);
return returned;
@ -591,7 +591,7 @@ uint8_t EightBit::MOS6502::add(uint8_t operand, uint8_t data, int carrying) noex
uint8_t EightBit::MOS6502::add_b(uint8_t operand, uint8_t data, int carrying) noexcept {
m_intermediate.word = operand + data + carrying;
set_flag(VF, negative(~(operand ^ data) & (operand ^ m_intermediate.low)));
adjustOverflow_add(operand, data, m_intermediate.low);
set_flag(CF, carry(m_intermediate.high));
adjustNZ(m_intermediate.low);
@ -612,7 +612,7 @@ uint8_t EightBit::MOS6502::add_d(uint8_t operand, uint8_t data, int carry) noexc
}
adjustNegative(high.low);
set_flag(VF, negative(~(operand ^ data) & (operand ^ high.low)));
adjustOverflow_add(operand, data, high.low);
if (high.word > 0x90)
high += 0x60;