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◆ main openmsx / src / cpu / Dasm.cc
5.9 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#include "Dasm.hh"
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#include "DasmTables.hh"
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#include "MSXCPUInterface.hh"
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#include "narrow.hh"
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#include "strCat.hh"
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namespace openmsx {
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using namespace std::literals;
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static constexpr char sign(uint8_t a)
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{
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	return (a & 128) ? '-' : '+';
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}
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static constexpr int abs(uint8_t a)
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{
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	return (a & 128) ? (256 - a) : a;
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}
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void appendAddrAsHex(std::string& output, uint16_t addr)
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{
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	strAppend(output, '#', hex_string<4>(addr));
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}
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std::optional<unsigned> instructionLength(std::span<const uint8_t> bin)
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{
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	if (bin.empty()) return {};
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	auto t = instr_len_tab[bin[0]];
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	if (t < 4) return t;
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	if (bin.size() < 2) return {};
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	t = instr_len_tab[64 * t + bin[1]];
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	if (t > bin.size()) return {};
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	return t;
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}
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unsigned dasm(std::span<const uint8_t> opcode, uint16_t pc, std::string& dest,
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              function_ref<void(std::string&, uint16_t)> appendAddr)
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{
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	std::string_view r;
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	auto [s, i] = [&] -> std::pair<const char*, unsigned> {
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		switch (opcode[0]) {
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			case 0xCB:
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				return {mnemonic_cb[opcode[1]], 2};
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			case 0xED:
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				return {mnemonic_ed[opcode[1]], 2};
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			case 0xDD:
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			case 0xFD:
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				r = (opcode[0] == 0xDD) ? "ix"sv : "iy"sv;
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				if (opcode[1] != 0xCB) {
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					return {mnemonic_xx[opcode[1]], 2};
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				} else {
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					return {mnemonic_xx_cb[opcode[3]], 4};
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				}
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			default:
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				return {mnemonic_main[opcode[0]], 1};
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		}
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	}();
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	for (int j = 0; s[j]; ++j) {
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		switch (s[j]) {
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		case 'B':
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			strAppend(dest, '#', hex_string<2>(
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				static_cast<uint16_t>(opcode[i])));
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			i += 1;
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			break;
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		case 'R':
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			appendAddr(dest, uint16_t(pc + 2 + static_cast<int8_t>(opcode[i])));
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			i += 1;
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			break;
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		case 'A':
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		case 'W':
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			appendAddr(dest, opcode[i] + opcode[i + 1] * 256);
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			i += 2;
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			break;
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		case 'X':
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			strAppend(dest, '(', r, sign(opcode[i]), '#',
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			     hex_string<2>(abs(opcode[i])), ')');
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			i += 1;
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			break;
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		case 'Y':
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			strAppend(dest, '(', r, sign(opcode[2]), '#',
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			     hex_string<2>(abs(opcode[2])), ')');
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			break;
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		case 'I':
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			dest += r;
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			break;
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		case '!':
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		case '@':
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		case '#': // invalid z80 instruction
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			strAppend(dest, "db");
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			for (auto k : xrange(i)) {
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				strAppend(dest, ((k == 0) ? ' ' : ','), '#', hex_string<2>(opcode[k]));
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			}
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			break;
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		case ' ': {
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			dest.resize(7, ' ');
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			break;
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		}
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		default:
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			dest += s[j];
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			break;
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		}
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	}
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	return i; // only used by unittest
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}
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std::span<uint8_t> fetchInstruction(const MSXCPUInterface& interface, uint16_t addr,
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                                    std::span<uint8_t, 4> buffer, EmuTime time)
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{
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	uint16_t idx = 0;
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	buffer[idx++] = interface.peekMem(addr, time);
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	auto len = instr_len_tab[buffer[0]];
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	if (len >= 4) {
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		buffer[idx++] = interface.peekMem(addr + 1, time);
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		len = instr_len_tab[64 * len + buffer[1]];
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		assert(len <= 4);
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	}
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	for (/**/; idx < len; ++idx) {
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		buffer[idx] = interface.peekMem(addr + idx, time);
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	}
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	return buffer.subspan(0, len);
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}
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unsigned dasm(const MSXCPUInterface& interface, uint16_t pc, std::span<uint8_t, 4> buf,
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              std::string& dest, EmuTime time,
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              function_ref<void(std::string&, uint16_t)> appendAddr)
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{
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	auto opcodes = fetchInstruction(interface, pc, buf, time);
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	dasm(opcodes, pc, dest, appendAddr);
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	return narrow_cast<unsigned>(opcodes.size());
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}
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static unsigned instructionLength(const MSXCPUInterface& interface, uint16_t pc,
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                                  EmuTime time)
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{
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	auto op0 = interface.peekMem(pc, time);
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	auto t = instr_len_tab[op0];
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	if (t < 4) return t;
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	auto op1 = interface.peekMem(pc + 1, time);
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	return instr_len_tab[64 * t + op1];
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}
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// Calculates an address smaller or equal to the given 'addr' where there is for
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// sure a boundary. Though this is not (yet) necessarily the largest address
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// with this property.
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// In addition return the length of the instruction at the resulting address.
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static std::pair<uint16_t, unsigned> findGuaranteedBoundary(const MSXCPUInterface& interface, uint16_t addr, EmuTime time)
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{
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	if (addr < 3) {
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		// address 0 (the top) is a boundary
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		return {0, instructionLength(interface, 0, time)};
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	}
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	std::array<unsigned, 4> length;
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	for (auto i : xrange(4)) {
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		length[i] = instructionLength(interface, uint16_t(addr - i), time);
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	}
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	while (true) {
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		// Criteria:
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		//   * Assuming a maximum instruction length of 4:
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		//   * IF  at 'addr - 1' starts an instruction with length 1
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		//   * and at 'addr - 2' starts an instruction with length 1 or 2
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		//   * and at 'addr - 3' starts an instruction with length 1 or 2 or 3
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		//   * THEN 'addr' must be the start of an instruction.
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		if ((length[1] == 1) && (length[2] <= 2) && (length[3] <= 3)) {
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			return {addr, length[0]};
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		}
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		if (addr == 3) {
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			// address 0 (the top) is a boundary
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			return {0, length[3]};
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		}
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		--addr;
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		length[0] = length[1];
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		length[1] = length[2];
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		length[2] = length[3];
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		length[3] = instructionLength(interface, addr - 3, time);
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	}
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}
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static std::pair<uint16_t, unsigned> instructionBoundaryAndLength(
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	const MSXCPUInterface& interface, uint16_t addr, EmuTime time)
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{
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	// scan backwards for a guaranteed boundary
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	auto [candidate, len] = findGuaranteedBoundary(interface, addr, time);
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	// scan forwards for the boundary with the largest address
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	while (true) {
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		if ((candidate + len) > addr) return {candidate, len};
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		candidate += len;
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		len = instructionLength(interface, candidate, time);
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	}
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}
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uint16_t instructionBoundary(const MSXCPUInterface& interface, uint16_t addr,
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                             EmuTime time)
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{
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	auto [result, len] = instructionBoundaryAndLength(interface, addr, time);
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	return result;
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}
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uint16_t nInstructionsBefore(const MSXCPUInterface& interface, uint16_t addr,
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                             EmuTime time, int n)
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{
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	auto start = uint16_t(std::max(0, int(addr - 4 * n))); // for sure small enough
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	auto [tmp, len] = instructionBoundaryAndLength(interface, start, time);
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	std::vector<uint16_t> addresses;
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	while ((tmp + len) <= addr) {
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		addresses.push_back(tmp);
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		tmp += len;
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		len = instructionLength(interface, tmp, time);
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	}
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	addresses.push_back(tmp);
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	return addresses[std::max(0, narrow<int>(addresses.size()) - 1 - n)];
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}
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} // namespace openmsx