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https://github.com/SourMesen/Mesen-S.git
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120 lines
2.5 KiB
C++
120 lines
2.5 KiB
C++
#include "stdafx.h"
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#include "AluMulDiv.h"
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#include "Cpu.h"
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#include "InternalRegisterTypes.h"
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#include "../Utilities/Serializer.h"
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void AluMulDiv::Initialize(Cpu* cpu)
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{
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_cpu = cpu;
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_state = {};
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_state.MultOperand1 = 0xFF;
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_state.Dividend = 0xFFFF;
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}
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void AluMulDiv::Run(bool isRead)
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{
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uint64_t cpuCycle = _cpu->GetCycleCount();
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if(isRead) {
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//Run 1 cycle less for read operations, since they occur earlier within the CPU cycle, compared to a write
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cpuCycle--;
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}
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if(_multCounter != 0 || _divCounter != 0) {
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uint64_t cyclesToRun = cpuCycle - _prevCpuCycle;
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while(cyclesToRun--) {
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if(!_multCounter && !_divCounter) {
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break;
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}
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if(_multCounter > 0) {
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_multCounter--;
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if(_state.DivResult & 0x01) {
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_state.MultOrRemainderResult += _shift;
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}
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_shift <<= 1;
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_state.DivResult >>= 1;
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}
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if(_divCounter > 0) {
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_divCounter--;
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_shift >>= 1;
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_state.DivResult <<= 1;
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if(_state.MultOrRemainderResult >= _shift) {
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_state.MultOrRemainderResult -= _shift;
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_state.DivResult |= 1;
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}
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}
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}
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}
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_prevCpuCycle = cpuCycle;
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}
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uint8_t AluMulDiv::Read(uint16_t addr)
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{
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Run(true);
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switch(addr) {
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case 0x4214: return (uint8_t)_state.DivResult;
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case 0x4215: return (uint8_t)(_state.DivResult >> 8);
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case 0x4216: return (uint8_t)_state.MultOrRemainderResult;
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case 0x4217: return (uint8_t)(_state.MultOrRemainderResult >> 8);
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}
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throw std::runtime_error("ALU: invalid address");
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}
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void AluMulDiv::Write(uint16_t addr, uint8_t value)
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{
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Run(false);
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switch(addr) {
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case 0x4202: _state.MultOperand1 = value; break;
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case 0x4203:
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_state.MultOrRemainderResult = 0;
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if(!_divCounter && !_multCounter) {
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_multCounter = 8;
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_state.MultOperand2 = value;
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_state.DivResult = (value << 8) | _state.MultOperand1;
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_shift = value;
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}
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break;
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case 0x4204: _state.Dividend = (_state.Dividend & 0xFF00) | value; break;
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case 0x4205: _state.Dividend = (_state.Dividend & 0xFF) | (value << 8); break;
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case 0x4206:
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_state.MultOrRemainderResult = _state.Dividend;
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if(!_divCounter && !_multCounter) {
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_divCounter = 16;
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_state.Divisor = value;
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_shift = (value << 16);
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}
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break;
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default: throw std::runtime_error("ALU: invalid address");
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}
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}
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AluState AluMulDiv::GetState()
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{
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return _state;
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}
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void AluMulDiv::Serialize(Serializer &s)
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{
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s.Stream(
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_state.MultOperand1, _state.MultOperand2, _state.MultOrRemainderResult, _state.Dividend, _state.Divisor, _state.DivResult,
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_divCounter, _multCounter, _shift, _prevCpuCycle
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);
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}
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