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Clean up decimal ADC.

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This commit is contained in:
Thomas Harte
2023-08-30 23:04:38 -04:00
parent 7b569b1a6c
commit 139a1a2acc
4 changed files with 59 additions and 9 deletions
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Processors/6502/6502.hpp
+1
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@@ -15,6 +15,7 @@
#include "../6502Esque/6502Esque.hpp"
#include "../6502Esque/Implementation/LazyFlags.hpp"
#include "../../Numeric/Carry.hpp"
#include "../../Numeric/RegisterSizes.hpp"
#include "../../ClockReceiver/ClockReceiver.hpp"
Processors/6502/Implementation/6502Implementation.hpp
+25 -9
View File
@@ -317,18 +317,34 @@ template <Personality personality, typename T, bool uses_ready_line> void Proces
case OperationADC:
if(flags_.decimal && has_decimal_mode(personality)) {
const uint16_t decimalResult = uint16_t(a_) + uint16_t(operand_) + uint16_t(flags_.carry);
uint8_t result = a_ + operand_ + flags_.carry;
flags_.zero_result = result;
flags_.carry = Numeric::carried_out<7>(a_, operand_, result);
uint8_t low_nibble = (a_ & 0xf) + (operand_ & 0xf) + flags_.carry;
if(low_nibble >= 0xa) low_nibble = ((low_nibble + 0x6) & 0xf) + 0x10;
uint16_t result = uint16_t(a_ & 0xf0) + uint16_t(operand_ & 0xf0) + uint16_t(low_nibble);
// The following effects the rule that only a single bit of carry can flow from the
// bottom nibble to the top: if that carry already happened, fix up the bottom without
// permitting another; otherwise if a fix up is required anyway due to the low digit nibble
// being out of range, permit the carry to happen (and check whether carry then left bit 7).
if(Numeric::carried_in<4>(a_, operand_, result)) {
result = (result & 0xf0) | ((result + 0x06) & 0x0f);
} else if((result & 0xf) > 0x9) {
flags_.carry |= result >= 0x100 - 0x6;
result += 0x06;
}
// 6502 quirk: N and V are set before the full result is computed but after the low nibble
// has been corrected.
flags_.negative_result = uint8_t(result);
flags_.overflow = (( (result^a_)&(result^operand_) )&0x80) >> 1;
if(result >= 0xa0) result += 0x60;
flags_.overflow = (( (result ^ a_) & (result ^ operand_) ) & 0x80) >> 1;
flags_.carry = (result >> 8) ? 1 : 0;
a_ = uint8_t(result);
flags_.zero_result = uint8_t(decimalResult);
if(Numeric::carried_out<7>(a_, operand_, result)) {
result += 0x60;
} else if (result >= 0xa0) {
flags_.carry = 1; // There'll now definitely be carry.
result += 0x60;
}
a_ = result;
if(is_65c02(personality)) {
flags_.set_nz(a_);