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Clean up decimal SBC implementation.

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This commit is contained in:
Thomas Harte 2023-08-31 15:02:17 -04:00
parent 13be247495
commit 39ee75d94a
2 changed files with 22 additions and 13 deletions
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4
OSBindings/Mac/Clock SignalTests/BCDTest.swift
View File

@ -48,6 +48,10 @@ class BCDTest: XCTestCase, CSTestMachineTrapHandler {
testBCD(processor: .processor65C02)
}
// func test6816BCD() {
// testBCD(processor: .processor65816)
// }
private var output: String = ""
func testMachine(_ testMachine: CSTestMachine, didTrapAtAddress address: UInt16) {
let machine6502 = testMachine as! CSTestMachine6502

31
Processors/6502/Implementation/6502Implementation.hpp
View File

@ -286,25 +286,30 @@ template <Personality personality, typename T, bool uses_ready_line> void Proces
[[fallthrough]];
case OperationSBC:
if(flags_.decimal && has_decimal_mode(personality)) {
const uint16_t notCarry = flags_.carry ^ 0x1;
const uint16_t decimalResult = uint16_t(a_) - uint16_t(operand_) - notCarry;
uint16_t temp16;
operand_ ^= 0xff;
uint8_t result = a_ + operand_ + flags_.carry;
temp16 = (a_&0xf) - (operand_&0xf) - notCarry;
if(temp16 > 0xf) temp16 -= 0x6;
temp16 = (temp16&0x0f) | ((temp16 > 0x0f) ? 0xfff0 : 0x00);
temp16 += (a_&0xf0) - (operand_&0xf0);
// All flags are set based only on the decimal result.
flags_.zero_result = result;
flags_.carry = Numeric::carried_out<7>(a_, operand_, result);
flags_.negative_result = result;
flags_.overflow = (( (result ^ a_) & (result ^ operand_) ) & 0x80) >> 1;
flags_.overflow = ( ( (decimalResult^a_)&(~decimalResult^operand_) )&0x80) >> 1;
flags_.negative_result = uint8_t(temp16);
flags_.zero_result = uint8_t(decimalResult);
// The bottom nibble is adjusted if there was carry into the top nibble;
// this doesn't cause additional carry.
if(!Numeric::carried_in<4>(a_, operand_, result)) {
result = (result & 0xf0) | ((result + 0x0a) & 0xf);
}
if(temp16 > 0xff) temp16 -= 0x60;
// The top nibble is adjusted only if there wasn't carry out of the whole byte.
if(!flags_.carry) {
result += 0xa0;
}
flags_.carry = (temp16 > 0xff) ? 0 : Flag::Carry;
a_ = uint8_t(temp16);
a_ = result;
if(is_65c02(personality)) {
// 65C02 fix: set the N and Z flags based on the final, decimal result.
flags_.set_nz(a_);
read_mem(operand_, address_.full);
break;