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Imports 6502-esque test for decimal SBC overflow.

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All applicable krom tests now pass.
This commit is contained in:
Thomas Harte 2020-11-03 20:37:30 -05:00
parent cc5ec78156
commit d50b059a17
2 changed files with 8 additions and 6 deletions
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2
Processors/6502/AllRAM/6502AllRAM.cpp
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@ -11,7 +11,7 @@
#include <algorithm>
#include <cstring>
#define BE_NOISY
//#define BE_NOISY
using namespace CPU::MOS6502;

12
Processors/65816/Implementation/65816Implementation.hpp
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@ -865,6 +865,11 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
#undef cp
// As implemented below, both ADC and SBC apply the 6502 test for overflow (i.e. based
// on intermediate results) rather than the 65C02 (i.e. based on the final result).
// This tracks the online tests I found, which hail from Nintendo world. So I'm currently
// unclear whether this is correct or merely a figment of Nintendo's custom chip.
case SBC:
if(registers_.flags.decimal) {
// I've yet to manage to find a rational way to map this to an ADC,
@ -872,6 +877,7 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
const uint16_t a = registers_.a.full & registers_.m_masks[1];
unsigned int result = 0;
unsigned int borrow = registers_.flags.carry ^ 1;
const uint16_t decimal_result = uint16_t(registers_.a.full - data_buffer_.value - borrow);
#define nibble(mask, adjustment, carry) \
result += (a & mask) - (data_buffer_.value & mask) - borrow; \
@ -886,7 +892,7 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
#undef nibble
registers_.flags.overflow = ~(( (result ^ registers_.a.full) & (result ^ data_buffer_.value) ) >> (1 + registers_.m_shift))&0x40;
registers_.flags.overflow = (( (decimal_result ^ registers_.a.full) & (~decimal_result ^ data_buffer_.value) ) >> (1 + registers_.m_shift))&0x40;
registers_.flags.set_nz(uint16_t(result), registers_.m_shift);
registers_.flags.carry = ((borrow >> 16)&1)^1;
LD(registers_.a, result, registers_.m_masks);
@ -901,10 +907,6 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
int result;
const uint16_t a = registers_.a.full & registers_.m_masks[1];
// As implemented below, this applies the 6502 test for overflow (i.e. based on the result
// prior to fixing up the final nibble) rather than the 65C02 (i.e. based on the final result).
// This tracks the online tests I found, which hail from Nintendo world. So I'm currently unclear
// whether this is correct or merely a figment of Nintendo's custom chip.
if(registers_.flags.decimal) {
uint16_t partials = 0;
result = registers_.flags.carry;