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decode.go
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decode.go
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/*
Copyright (c) 2019-2021 Andreas T Jonsson
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
*/
package cpu
import (
"log"
"runtime"
"time"
"github.com/andreas-jonsson/virtualxt/emulator/memory"
"github.com/andreas-jonsson/virtualxt/emulator/processor"
"github.com/andreas-jonsson/virtualxt/emulator/processor/validator"
)
var zero16 uint16
type instructionState struct {
opcode, modRegRM,
repeatMode byte
isWide, rmToReg,
halted bool
decodeAt uint16
segOverride *uint16
cycleCount int
}
func (p *CPU) getReg() byte {
return (p.modRegRM >> 3) & 7
}
func (p *CPU) regLocation() dataLocation {
return dataLocation(p.getReg()) | registerLocation
}
func (p *CPU) segLocation() dataLocation {
return dataLocation(p.getReg()) | segmentLocation
}
func (p *CPU) rmLocation() dataLocation {
idx := p.modRegRM & 0xC7
f := modRMLookup[idx]
return f(p)
}
func (p *CPU) peakOpcodeStream() byte {
return p.ReadByte(memory.NewPointer(p.CS, p.IP))
}
func (p *CPU) readOpcodeStream() byte {
v := p.peakOpcodeStream()
p.IP++
return v
}
func (p *CPU) readOpcodeImm16() uint16 {
v := p.ReadWord(memory.NewPointer(p.CS, p.IP))
p.IP += 2
return v
}
func (p *CPU) readModRegRM() {
p.modRegRM = p.readOpcodeStream()
}
func (p *CPU) parseOperands() (dataLocation, dataLocation) {
p.readModRegRM()
reg, rm := p.regLocation(), p.rmLocation()
if p.rmToReg {
return reg, rm
}
return rm, reg
}
func (p *CPU) parseOpcode() {
p.segOverride = nil
p.repeatMode = 0
p.decodeAt = p.IP
var op byte
loop:
for {
switch op = p.readOpcodeStream(); op {
case 0x26: // ES:
p.segOverride = &p.ES
case 0x2E: // CS:
p.segOverride = &p.CS
case 0x36: // SS:
p.segOverride = &p.SS
case 0x3E: // DS:
p.segOverride = &p.DS
case 0xF0: // LOCK
// NOP...
case 0xF2, 0xF3: // REPNE/REPNZ,REP/REPE/REPZ
p.repeatMode = op
default:
break loop
}
}
p.opcode = op
p.isWide = op&1 != 0
p.rmToReg = op&2 != 0
}
func (p *CPU) packFlags8() byte {
var flags byte = 0x2
if p.CF {
flags |= 0x001
}
if p.PF {
flags |= 0x004
}
if p.AF {
flags |= 0x010
}
if p.ZF {
flags |= 0x040
}
if p.SF {
flags |= 0x080
}
return flags
}
func (p *CPU) packFlags16() uint16 {
flags := uint16(p.packFlags8())
if p.TF {
flags |= 0x100
}
if p.IF {
flags |= 0x200
}
if p.DF {
flags |= 0x400
}
if p.OF {
flags |= 0x800
}
return flags
}
func (p *CPU) unpackFlags8(flags byte) {
p.CF = flags&0x001 != 0
p.PF = flags&0x004 != 0
p.AF = flags&0x010 != 0
p.ZF = flags&0x040 != 0
p.SF = flags&0x080 != 0
}
func (p *CPU) unpackFlags16(flags uint16) {
p.unpackFlags8(byte(flags & 0xFF))
p.TF = flags&0x100 != 0
p.IF = flags&0x200 != 0
p.DF = flags&0x400 != 0
p.OF = flags&0x800 != 0
}
func signExtend16(v byte) uint16 {
if v&0x80 != 0 {
return uint16(v) | 0xFF00
}
return uint16(v)
}
func signExtend32(v uint16) uint32 {
if v&0x8000 != 0 {
return uint32(v) | 0xFFFF0000
}
return uint32(v)
}
func (p *CPU) stackTop() memory.Pointer {
return memory.NewPointer(p.SS, p.SP)
}
func (p *CPU) push16(v uint16) {
p.SP -= 2
p.WriteWord(p.stackTop(), v)
}
func (p *CPU) pop16() uint16 {
v := p.ReadWord(p.stackTop())
p.SP += 2
return v
}
func (p *CPU) updateFlagsSZP8(res byte) {
p.SF = res&0x80 != 0
p.ZF = res == 0
p.PF = parityLookup[res]
}
func (p *CPU) updateFlagsSZP16(res uint16) {
p.SF = res&0x8000 != 0
p.ZF = res == 0
p.PF = parityLookup[res&0xFF]
}
func (p *CPU) getFlagsMask() (uint32, uint32) {
maskC := uint32(0xFF00)
maskO := uint32(0x0080)
if p.isWide {
maskC = 0xFFFF0000
maskO = 0x00008000
}
return maskC, maskO
}
func (p *CPU) clearFlagsOC() {
p.CF = false
p.OF = false
}
func (p *CPU) updateFlagsOSZPCLog8(res byte) {
p.updateFlagsSZP8(res)
p.clearFlagsOC()
}
func (p *CPU) updateFlagsOSZPCLog16(res uint16) {
p.updateFlagsSZP16(res)
p.clearFlagsOC()
}
func (p *CPU) updateFlagsOACAdd(res, a, b uint32) {
maskC, maskO := p.getFlagsMask()
p.CF = res&maskC != 0
p.AF = ((a ^ b ^ res) & 0x10) == 0x10
p.OF = ((res ^ a) & (res ^ b) & maskO) == maskO
}
func (p *CPU) updateFlagsOACSub(res, a, b uint32) {
maskC, maskO := p.getFlagsMask()
p.CF = res&maskC != 0
p.AF = ((a ^ b ^ res) & 0x10) != 0
p.OF = ((res ^ a) & (a ^ b) & maskO) != 0
}
func (p *CPU) updateFlagsOACSubCarry(res, a, b uint32) {
b += b2ui32(p.CF)
p.updateFlagsOACSub(res, a, b)
}
func b2ui16(b bool) uint16 {
if b {
return 1
}
return 0
}
func b2ui32(b bool) uint32 {
return uint32(b2ui16(b))
}
func opXCHG(a, b *uint16) {
tmp := *a
*a = *b
*b = tmp
}
func (p *CPU) getSeg(seg uint16) uint16 {
if p.segOverride != nil {
return *p.segOverride
}
return seg
}
func (p *CPU) divisionByZero() {
p.IP = p.decodeAt
p.doInterrupt(0)
}
func (p *CPU) doInterrupt(n int) {
p.stats.NumInterrupts++
validator.Discard()
p.halted = false
if handler := p.interceptors[n]; handler != nil {
if err := handler.HandleInterrupt(n); err == nil {
p.TF, p.IF = false, false
return
} else if err != processor.ErrInterruptNotHandled {
log.Panic(err)
}
}
p.push16(p.packFlags16())
p.push16(p.CS)
p.push16(p.IP)
offset := n * 4
p.CS = p.ReadWord(memory.Pointer(offset + 2))
p.IP = p.ReadWord(memory.Pointer(offset))
p.TF, p.IF = false, false
}
func (p *CPU) Step() (int, error) {
// Reset cycle counter.
p.cycleCount = 0
if p.trap {
p.doInterrupt(1)
}
p.trap = p.TF
if !p.trap && p.IF {
if n, err := p.pic.GetInterrupt(); err == nil {
p.doInterrupt(n)
}
}
if p.halted {
return 0, processor.ErrCPUHalt
}
p.parseOpcode()
if p.repeatMode != 0 {
err := p.doRepeat()
return p.cycleCount, err
}
validator.Begin(p.opcode, p.Registers)
if err := p.execute(); err != nil {
return p.cycleCount, err
}
validator.End(p.Registers)
for _, d := range p.peripherals {
if err := d.Step(p.cycleCount); err != nil {
return p.cycleCount, err
}
}
return p.cycleCount, nil
}
func (p *CPU) execute() error {
// All instructions are 1 cycle right now.
p.cycleCount++
op := p.opcode
carry := op > 0x0F && p.CF
carryOp := b2ui32(carry)
switch op {
case 0x00, 0x02, 0x10, 0x12: // ADD/ADC r/m8,r8
dest, src := p.parseOperands()
a, b := uint32(dest.readByte(p)), uint32(src.readByte(p))
res := a + b + carryOp
dest.writeByte(p, byte(res))
p.updateFlagsSZP8(byte(res))
p.updateFlagsOACAdd(res, a, b)
case 0x01, 0x03, 0x11, 0x13: // ADD/ADC r/m16,r16
dest, src := p.parseOperands()
a, b := uint32(dest.readWord(p)), uint32(src.readWord(p))
res := a + b + carryOp
dest.writeWord(p, uint16(res))
p.updateFlagsSZP16(uint16(res))
p.updateFlagsOACAdd(res, a, b)
case 0x04, 0x14: // ADD/ADC AL,d8
a, b := uint32(p.AL()), uint32(p.readOpcodeStream())
res := a + b + carryOp
p.SetAL(byte(res))
p.updateFlagsSZP8(byte(res))
p.updateFlagsOACAdd(res, a, b)
case 0x05, 0x15: // ADD/ADC AX,d16
a, b := uint32(p.AX), uint32(p.readOpcodeImm16())
res := a + b + carryOp
p.AX = uint16(res)
p.updateFlagsSZP16(uint16(res))
p.updateFlagsOACAdd(res, a, b)
case 0x06: // PUSH ES
p.push16(p.ES)
case 0x07: // POP ES
p.ES = p.pop16()
case 0x08, 0x0A: // OR r/m8,r8
dest, src := p.parseOperands()
a, b := dest.readByte(p), src.readByte(p)
res := a | b
dest.writeByte(p, res)
p.updateFlagsOSZPCLog8(res)
case 0x09, 0x0B: // OR r/m16,r16
dest, src := p.parseOperands()
a, b := dest.readWord(p), src.readWord(p)
res := a | b
dest.writeWord(p, res)
p.updateFlagsOSZPCLog16(res)
case 0x0C: // OR AL,d8
a, b := p.AL(), p.readOpcodeStream()
res := a | b
p.SetAL(res)
p.updateFlagsOSZPCLog8(res)
case 0x0D: // OR AX,d16
p.AX = p.AX | p.readOpcodeImm16()
p.updateFlagsOSZPCLog16(p.AX)
case 0x0E: // PUSH CS
p.push16(p.CS)
case 0x0F: // *POP CS
if !p.isV20 {
p.CS = p.pop16()
}
// 0x1x
case 0x16: // PUSH SS
p.push16(p.SS)
case 0x17: // POP SS
p.SS = p.pop16()
case 0x18, 0x1A: // SBB r/m8,r8
dest, src := p.parseOperands()
a, b := uint32(dest.readByte(p)), uint32(src.readByte(p))
res := a - (b + carryOp)
dest.writeByte(p, byte(res))
p.updateFlagsSZP8(byte(res))
p.updateFlagsOACSubCarry(res, a, b)
case 0x19, 0x1B: // SBB r/m16,r16
dest, src := p.parseOperands()
a, b := uint32(dest.readWord(p)), uint32(src.readWord(p))
res := a - (b + carryOp)
dest.writeWord(p, uint16(res))
p.updateFlagsSZP16(uint16(res))
p.updateFlagsOACSubCarry(res, a, b)
case 0x1C: // SBB AL,d8
a, b := uint32(p.AL()), uint32(p.readOpcodeStream())
res := a - (b + carryOp)
p.SetAL(byte(res))
p.updateFlagsSZP8(byte(res))
p.updateFlagsOACSubCarry(res, a, b)
case 0x1D: // SBB AX,d16
a, b := uint32(p.AX), uint32(p.readOpcodeImm16())
res := a - (b + carryOp)
p.updateFlagsSZP16(uint16(res))
p.updateFlagsOACSubCarry(res, a, b)
case 0x1E: // PUSH DS
p.push16(p.DS)
case 0x1F: // POP DS
p.DS = p.pop16()
// 0x2x
case 0x20, 0x22: // AND r/m8,r8
dest, src := p.parseOperands()
a, b := dest.readByte(p), src.readByte(p)
res := uint16(a) & uint16(b)
dest.writeByte(p, byte(res))
p.updateFlagsOSZPCLog8(byte(res))
case 0x21, 0x23: // AND r/m16,r16
dest, src := p.parseOperands()
a, b := dest.readWord(p), src.readWord(p)
res := uint32(a) & uint32(b)
dest.writeWord(p, uint16(res))
p.updateFlagsOSZPCLog16(uint16(res))
case 0x24: // AND AL,d8
a, b := p.AL(), p.readOpcodeStream()
res := uint16(a) & uint16(b)
p.SetAL(byte(res))
p.updateFlagsOSZPCLog8(byte(res))
case 0x25: // AND AX,d16
b := p.readOpcodeImm16()
res := uint32(p.AX) & uint32(b)
p.AX = uint16(res)
p.updateFlagsOSZPCLog16(uint16(res))
case 0x27: // DAA
if al := p.AL(); ((al & 0xF) > 9) || p.AF {
v := uint16(al) + 6
p.SetAL(byte(v & 0xFF))
p.CF = (v & 0xFF00) != 0
p.AF = true
} else {
p.AF = false
}
if al := p.AL(); ((al & 0xF0) > 0x90) || p.CF {
p.SetAL(al + 0x60)
p.CF = true
} else {
p.CF = false
}
al := p.AL()
p.SetAL(al)
p.updateFlagsSZP8(al)
case 0x28, 0x2A: // SUB r/m8,r8
dest, src := p.parseOperands()
a, b := uint32(dest.readByte(p)), uint32(src.readByte(p))
res := a - b
dest.writeByte(p, byte(res))
p.updateFlagsSZP8(byte(res))
p.updateFlagsOACSub(res, a, b)
case 0x29, 0x2B: // SUB r/m16,r16
dest, src := p.parseOperands()
a, b := uint32(dest.readWord(p)), uint32(src.readWord(p))
res := a - b
dest.writeWord(p, uint16(res))
p.updateFlagsSZP16(uint16(res))
p.updateFlagsOACSub(res, a, b)
case 0x2C: // SUB AL,d8
a, b := uint32(p.AL()), uint32(p.readOpcodeStream())
res := a - b
p.SetAL(byte(res))
p.updateFlagsSZP8(byte(res))
p.updateFlagsOACSub(res, a, b)
case 0x2D: // SUB AX,d16
a, b := uint32(p.AX), uint32(p.readOpcodeImm16())
res := a - b
p.AX = uint16(res)
p.updateFlagsSZP16(uint16(res))
p.updateFlagsOACSub(res, a, b)
case 0x2F: // DAS
if al := p.AL(); ((al & 15) > 9) || p.AF {
v := uint16(al) - 6
p.SetAL(byte(v & 0xFF))
p.CF = (v & 0xFF00) != 0
p.AF = true
} else {
p.AF = false
}
if al := p.AL(); ((al & 0xF0) > 0x90) || p.CF {
p.SetAL(al - 0x60)
p.CF = true
} else {
p.CF = false
}
p.updateFlagsSZP8(p.AL())
// 0x3x
case 0x30, 0x32: // XOR r/m8,r8
dest, src := p.parseOperands()
a, b := dest.readByte(p), src.readByte(p)
res := uint16(a) ^ uint16(b)
dest.writeByte(p, byte(res))
p.updateFlagsOSZPCLog8(byte(res))
case 0x31, 0x33: // XOR r/m16,r16
dest, src := p.parseOperands()
a, b := dest.readWord(p), src.readWord(p)
res := uint32(a) ^ uint32(b)
dest.writeWord(p, uint16(res))
p.updateFlagsOSZPCLog16(uint16(res))
case 0x34: // XOR AL,d8
a, b := p.AL(), p.readOpcodeStream()
res := uint16(a) ^ uint16(b)
p.SetAL(byte(res))
p.updateFlagsOSZPCLog8(byte(res))
case 0x35: // XOR AX,d16
b := p.readOpcodeImm16()
res := uint32(p.AX) ^ uint32(b)
p.AX = uint16(res)
p.updateFlagsOSZPCLog16(uint16(res))
case 0x37: // AAA
if al := p.AL(); ((al & 0xF) > 9) || p.AF {
p.SetAL(al + 6)
p.SetAH(p.AH() + 1)
p.AF, p.CF = true, true
} else {
p.AF, p.CF = false, false
}
al := p.AL() & 0xF
p.SetAL(al)
p.updateFlagsSZP8(al)
case 0x38, 0x3A: // CMP r/m8,r8
dest, src := p.parseOperands()
a, b := uint32(dest.readByte(p)), uint32(src.readByte(p))
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP8(byte(res))
case 0x39, 0x3B: // CMP r/m16,r16
dest, src := p.parseOperands()
a, b := uint32(dest.readWord(p)), uint32(src.readWord(p))
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP16(uint16(res))
case 0x3C: // CMP AL,d8
a, b := uint32(p.AL()), uint32(p.readOpcodeStream())
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP8(byte(res))
case 0x3D: // CMP AX,d16
a, b := uint32(p.AX), uint32(p.readOpcodeImm16())
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP16(uint16(res))
case 0x3F: // AAS
if al := p.AL(); ((al & 0xF) > 9) || p.AF {
p.SetAL(al - 6)
p.SetAH(p.AH() - 1)
p.AF, p.CF = true, true
} else {
p.AF, p.CF = false, false
}
al := p.AL() & 0xF
p.SetAL(al)
p.updateFlagsSZP8(al)
// 0x4x
case 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47: // INC AX/CX/DX/BX/SP/BP/SI/DI
reg := dataLocation(op-0x40) | registerLocation
a := reg.readWord(p)
res := a + 1
reg.writeWord(p, res)
cf := p.CF
p.updateFlagsOACAdd(uint32(res), uint32(a), 1)
p.updateFlagsSZP16(res)
p.CF = cf
case 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F: // DEC AX/CX/DX/BX/SP/BP/SI/DI
reg := dataLocation(op-0x40) | registerLocation
a := reg.readWord(p)
res := a - 1
reg.writeWord(p, res)
cf := p.CF
p.updateFlagsOACSub(uint32(res), uint32(a), 1)
p.updateFlagsSZP16(res)
p.CF = cf
// 0x5x
case 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57: // PUSH AX/CX/DX/BX/SP/BP/SI/DI
p.push16((dataLocation(op-0x50) | registerLocation).readWord(p))
case 0x58, 0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F: // POP AX/CX/DX/BX/SP/BP/SI/DI
(dataLocation(op-0x58) | registerLocation).writeWord(p, p.pop16())
// 0x6x
case 0x60: // PUSHA (80186)
if p.isV20 {
sp := p.SP
p.push16(p.AX)
p.push16(p.CX)
p.push16(p.DX)
p.push16(p.BX)
p.push16(sp)
p.push16(p.BP)
p.push16(p.SI)
p.push16(p.DI)
} else {
p.invalidOpcode()
}
case 0x61: // POPA (80186)
if p.isV20 {
p.DI = p.pop16()
p.SI = p.pop16()
p.BP = p.pop16()
p.pop16()
p.BX = p.pop16()
p.DX = p.pop16()
p.CX = p.pop16()
p.AX = p.pop16()
} else {
p.invalidOpcode()
}
case 0x62: // BOUND (80186)
if p.isV20 {
p.readModRegRM()
idx := signExtend32(p.regLocation().readWord(p))
addr := p.rmLocation().getAddress()
if idx < signExtend32(p.ReadWord(addr.Pointer())) || idx > signExtend32(p.ReadWord(addr.AddInt(2).Pointer())) {
p.IP = p.decodeAt
p.doInterrupt(5)
}
} else {
p.invalidOpcode()
}
case 0x68: // PUSH d16 (80186)
if p.isV20 {
p.push16(p.readOpcodeImm16())
} else {
p.invalidOpcode()
}
case 0x69, 0x6B: // IMUL r/m16,d8/d16 (80186)
if p.isV20 {
p.readModRegRM()
dest := p.rmLocation()
a := signExtend32(dest.readWord(p))
var res uint32
if op == 69 {
res = a * signExtend32(signExtend16(p.readOpcodeStream()))
} else {
res = a * signExtend32(p.readOpcodeImm16())
}
res16 := uint16(res & 0xFFFF)
upper := uint16(res >> 16)
dest.writeWord(p, res16)
p.updateFlagsSZP16(res16)
if res16&0x8000 == 0x8000 {
p.CF = upper != 0xFFFF
} else {
p.CF = upper != 0x0
}
p.OF = p.CF
} else {
p.invalidOpcode()
}
case 0x6A: // PUSH d8 (80186)
if p.isV20 {
p.push16(uint16(p.readOpcodeStream()))
} else {
p.invalidOpcode()
}
case 0x6C: // INSB (80186)
if p.isV20 {
p.WriteByte(memory.NewPointer(p.getSeg(p.DS), p.SI), p.InByte(p.DX))
p.updateDISI()
} else {
p.invalidOpcode()
}
case 0x6D: // INSW (80186)
if p.isV20 {
p.WriteWord(memory.NewPointer(p.getSeg(p.DS), p.SI), p.InWord(p.DX))
p.updateDISI()
} else {
p.invalidOpcode()
}
case 0x6E: // OUTSB (80186)
if p.isV20 {
p.OutByte(p.DX, p.ReadByte(memory.NewPointer(p.getSeg(p.DS), p.SI)))
p.updateDISI()
} else {
p.invalidOpcode()
}
case 0x6F: // OUTSW (80186)
if p.isV20 {
p.OutWord(p.DX, p.ReadWord(memory.NewPointer(p.getSeg(p.DS), p.SI)))
p.updateDISI()
} else {
p.invalidOpcode()
}
// 0x7x
case 0x70: // JO rel8
p.jmpRel8Cond(p.OF)
case 0x71: // JNO rel8
p.jmpRel8Cond(!p.OF)
case 0x72: // JB/JNAE rel8
p.jmpRel8Cond(p.CF)
case 0x73: // JNB/JAE rel8
p.jmpRel8Cond(!p.CF)
case 0x74: // JE/JZ rel8
p.jmpRel8Cond(p.ZF)
case 0x75: // JNE/JNZ rel8
p.jmpRel8Cond(!p.ZF)
case 0x76: // JBE/JNA rel8
p.jmpRel8Cond(p.CF || p.ZF)
case 0x77: // JNBE/JA rel8
p.jmpRel8Cond(!p.CF && !p.ZF)
case 0x78: // JS rel8
p.jmpRel8Cond(p.SF)
case 0x79: // JNS rel8
p.jmpRel8Cond(!p.SF)
case 0x7A: // JP/JPE rel8
p.jmpRel8Cond(p.PF)
case 0x7B: // JNP/JPO rel8
p.jmpRel8Cond(!p.PF)
case 0x7C: // JL/JNGE rel8
p.jmpRel8Cond(p.SF != p.OF)
case 0x7D: // JNL/JGE rel8
p.jmpRel8Cond(p.SF == p.OF)
case 0x7E: // JLE/JNG rel8
p.jmpRel8Cond(p.SF != p.OF || p.ZF)
case 0x7F: // JNLE/JG rel8
p.jmpRel8Cond(!p.ZF && p.SF == p.OF)
// 0x8x
case 0x80, 0x82: // _ALU1 r/m8,d8
p.grp1()
case 0x81, 0x83: // _ALU1 r/m16,d16
p.grp1w()
case 0x84: // TEST r/m8,r8
p.readModRegRM()
a, b := p.rmLocation().readByte(p), p.regLocation().readByte(p)
p.updateFlagsOSZPCLog8(a & b)
case 0x85: // TEST r/m16,r16
p.readModRegRM()
a, b := p.rmLocation().readWord(p), p.regLocation().readWord(p)
p.updateFlagsOSZPCLog16(a & b)
case 0x86: // XCHG r8,r/m8
p.readModRegRM()
dst, src := p.regLocation(), p.rmLocation()
d, s := dst.readByte(p), src.readByte(p)
dst.writeByte(p, s)
src.writeByte(p, d)
case 0x87: // XCHG r16,r/m16
p.readModRegRM()
dst, src := p.regLocation(), p.rmLocation()
d, s := dst.readWord(p), src.readWord(p)
dst.writeWord(p, s)
src.writeWord(p, d)
case 0x88, 0x8A: // MOV r/m8,r8
dest, src := p.parseOperands()
dest.writeByte(p, src.readByte(p))
case 0x89, 0x8B: // MOV r/m16,r16
dest, src := p.parseOperands()
dest.writeWord(p, src.readWord(p))
case 0x8C: // _MOV r/m16,sr
p.readModRegRM()
p.rmLocation().writeWord(p, p.segLocation().readWord(p))
case 0x8D: // LEA r16,r/m16
p.readModRegRM()
p.segOverride = &zero16
addr := p.rmLocation().getPointer()
p.regLocation().writeWord(p, uint16(addr))
case 0x8E: // _MOV sr,r/m16
p.readModRegRM()
p.segLocation().writeWord(p, p.rmLocation().readWord(p))
case 0x8F: // _POP r/m16
p.readModRegRM()
p.rmLocation().writeWord(p, p.pop16())
// 0x9x
case 0x90: // NOP
p.stats.NOP++
case 0x91: // XCHG AX,CX
opXCHG(&p.AX, &p.CX)
case 0x92: // XCHG AX,DX
opXCHG(&p.AX, &p.DX)
case 0x93: // XCHG AX,BX
opXCHG(&p.AX, &p.BX)
case 0x94: // XCHG AX,SP
opXCHG(&p.AX, &p.SP)
case 0x95: // XCHG AX,BP
opXCHG(&p.AX, &p.BP)
case 0x96: // XCHG AX,SI
opXCHG(&p.AX, &p.SI)
case 0x97: // XCHG AX,DI
opXCHG(&p.AX, &p.DI)
case 0x98: // CBW
p.AX = signExtend16(p.AL())
case 0x99: // CWD
if p.AX&0x8000 != 0 {
p.DX = 0xFFFF
} else {
p.DX = 0
}
case 0x9A: // CALL seg:a16
ip := p.readOpcodeImm16()
cs := p.readOpcodeImm16()
p.push16(p.CS)
p.push16(p.IP)
p.IP, p.CS = ip, cs
case 0x9B: // WAIT
case 0x9C: // PUSHF
p.push16(p.packFlags16())
case 0x9D: // POPF
p.unpackFlags16(p.pop16())
case 0x9E: // SAHF
p.unpackFlags8(p.AH())
case 0x9F: // LAHF
p.SetAH(p.packFlags8())
// 0xAx
case 0xA0: // MOV AL,[addr]
p.SetAL(p.ReadByte(memory.NewPointer(p.getSeg(p.DS), p.readOpcodeImm16())))
case 0xA1: // MOV AX,[addr]
p.AX = p.ReadWord(memory.NewPointer(p.getSeg(p.DS), p.readOpcodeImm16()))
case 0xA2: // MOV [addr],AL
p.WriteByte(memory.NewPointer(p.getSeg(p.DS), p.readOpcodeImm16()), p.AL())
case 0xA3: // MOV [addr],AX
p.WriteWord(memory.NewPointer(p.getSeg(p.DS), p.readOpcodeImm16()), p.AX)
case 0xA4: // MOVSB
p.WriteByte(memory.NewPointer(p.ES, p.DI), p.ReadByte(memory.NewPointer(p.getSeg(p.DS), p.SI)))
p.updateDISI()
case 0xA5: // MOVSW
p.WriteWord(memory.NewPointer(p.ES, p.DI), p.ReadWord(memory.NewPointer(p.getSeg(p.DS), p.SI)))
p.updateDISI()
case 0xA6: // CMPSB
a, b := uint32(p.ReadByte(memory.NewPointer(p.getSeg(p.DS), p.SI))), uint32(p.ReadByte(memory.NewPointer(p.ES, p.DI)))
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP8(byte(res))
p.updateDISI()
case 0xA7: // CMPSW
a, b := uint32(p.ReadWord(memory.NewPointer(p.getSeg(p.DS), p.SI))), uint32(p.ReadWord(memory.NewPointer(p.ES, p.DI)))
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP16(uint16(res))
p.updateDISI()
case 0xA8: // TEST AL,d8
p.updateFlagsSZP8(p.AL() & p.readOpcodeStream())
case 0xA9: // TEST AX,d16
p.updateFlagsSZP16(p.AX & p.readOpcodeImm16())
case 0xAA: // STOSB
p.WriteByte(memory.NewPointer(p.ES, p.DI), p.AL())
p.updateDI()
case 0xAB: // STOSW
p.WriteWord(memory.NewPointer(p.ES, p.DI), p.AX)
p.updateDI()
case 0xAC: // LODSB
p.SetAL(p.ReadByte(memory.NewPointer(p.getSeg(p.DS), p.SI)))
p.updateSI()
case 0xAD: // LODSW
p.AX = p.ReadWord(memory.NewPointer(p.getSeg(p.DS), p.SI))
p.updateSI()
case 0xAE: // SCASB
a, b := uint32(p.AL()), uint32(p.ReadByte(memory.NewPointer(p.ES, p.DI)))
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP8(byte(res))
p.updateDI()
case 0xAF: // SCASW
a, b := uint32(p.AX), uint32(p.ReadWord(memory.NewPointer(p.ES, p.DI)))
res := a - b
p.updateFlagsOACSub(res, a, b)
p.updateFlagsSZP16(uint16(res))
p.updateDI()
// 0xBx
case 0xB0, 0xB1, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7: // MOV AL/CL/DL/BL/AH/CH/DH/BH,d8
(dataLocation(op-0xB0) | registerLocation).writeByte(p, p.readOpcodeStream())
case 0xB8, 0xB9, 0xBA, 0xBB, 0xBC, 0xBD, 0xBE, 0xBF: // MOV AX/CX/DX/BX/SP/BP/SI/DI,d16
(dataLocation(op-0xB8) | registerLocation).writeWord(p, p.readOpcodeImm16())
// 0xCx
case 0xC0: // SHL r/m8,d8 (80186)
if p.isV20 {
p.readModRegRM()
dest := p.rmLocation()
dest.writeByte(p, p.shiftOrRotate8(p.getReg(), dest.readByte(p), p.readOpcodeStream()))
} else {
p.invalidOpcode()
}
case 0xC1: // SHL r/m16,d16 (80186)
if p.isV20 {
p.readModRegRM()
dest := p.rmLocation()
dest.writeWord(p, p.shiftOrRotate16(p.getReg(), dest.readWord(p), p.readOpcodeStream()))
} else {
p.invalidOpcode()
}
case 0xC2: // RET d16
ip := p.pop16()
p.SP += p.readOpcodeImm16()
p.IP = ip
case 0xC3: // RET
p.IP = p.pop16()
case 0xC4: // LES r16,m32
p.readModRegRM()
addr := p.rmLocation().getAddress()
p.regLocation().writeWord(p, p.ReadWord(addr.Pointer()))
p.ES = p.ReadWord(addr.AddInt(2).Pointer())
case 0xC5: // LDS r16,m32
p.readModRegRM()
addr := p.rmLocation().getAddress()
p.regLocation().writeWord(p, p.ReadWord(addr.Pointer()))
p.DS = p.ReadWord(addr.AddInt(2).Pointer())
case 0xC6: // _MOV r/m8,d8
p.readModRegRM()
p.rmLocation().writeByte(p, p.readOpcodeStream())
case 0xC7: // _MOV r/m16,d16
p.readModRegRM()
p.rmLocation().writeWord(p, p.readOpcodeImm16())
case 0xC8: // ENTER (80186)
if p.isV20 {
size := p.readOpcodeImm16()
level := p.readOpcodeStream()
p.push16(p.BP)
sp := p.SP
if level > 0 {
for i := 1; i < int(level); i++ {
p.BP -= 2
p.push16(p.BP)
}
p.push16(p.SP)
}
p.BP = sp
p.SP = sp - size
} else {