/*
 *      Interactive disassembler (IDA).
 *      Copyright (c) 1990-98 by Ilfak Guilfanov.
 *      ALL RIGHTS RESERVED.
 *                              E-mail: ig@estar.msk.su, ig@datarescue.com
 *                              FIDO:   2:5020/209
 *
 */

#include "xa.hpp"

static int ana_basic(void);

//----------------------------------------------------------------------
inline int ua_next_word_be(void)
{
  long result;
  result = ((uchar)ua_next_byte()) << 8;
  result += (uchar)ua_next_byte();
  return (int)result;
}

//----------------------------------------------------------------------
inline void opC(op_t &op)
{
  op.type = o_reg;
  op.reg = rC;
}

//----------------------------------------------------------------------
// register direct
static int op_rd(op_t &x, int reg, int dtyp)
{
  x.type = o_reg;
  x.dtyp = dtyp;
  x.reg  = (dtyp == dt_byte ? rR0L : rR0) + reg;
  return 1;
}

//----------------------------------------------------------------------
// register indirect
static int op_ph(op_t &x, int phrase, int reg, int dtyp)
{
  x.type = o_phrase;
  x.dtyp = dtyp;
  x.phrase  = phrase; // union with x.reg
  x.indreg = reg;
  if ((phrase != fRlistL) && (phrase != fRlistH)) x.indreg += rR0;
  return 1;
}

//----------------------------------------------------------------------
// register indirect with displacement
static int op_ds(op_t &x, int phrase, int ireg, sval_t disp, int dtyp)
{
  if (disp > 0xFD00L)
  {
    disp = disp - 0x10000L; // heuristics: treat large values from -300h as negative
  }
  x.type = o_displ;
  x.dtyp = dtyp;
  x.phrase = phrase;
  x.indreg = rR0 + ireg;
  x.addr = disp;
  return 1;
}

//----------------------------------------------------------------------
inline void op_mm(op_t &x, uval_t addr, int dtyp)
{
  x.type = o_mem;
  x.dtyp = dtyp;
  x.addr = addr;
}

//----------------------------------------------------------------------
inline void op_rel(op_t &x, sval_t addr)
{
  if (addr>32767) addr -= 0x10000L;
  x.type = o_near;
  x.dtyp = dt_code;
  x.addr = (cmd.ip + cmd.size + 2*addr) & (~1L);
}

//----------------------------------------------------------------------
inline void op_near(op_t &x, uval_t addr)
{
  x.type = o_near;
  x.dtyp = dt_word;
  x.addr = addr;
}

//----------------------------------------------------------------------
inline void op_im(op_t &x, uval_t value, int dtyp)
{
  x.type  = o_imm;
  x.dtyp  = dtyp;
  x.value = value;
}

//----------------------------------------------------------------------
inline void op_bit(op_t &x, int type, uval_t addr)
{
  x.type = type;
  x.dtyp = dt_word;
  x.addr = addr;
}

//----------------------------------------------------------------------
// analyze an basic instruction
static int ana_basic(void)
{

  static enum nameNum xa_basic[] = {
	XA_add, XA_addc, XA_sub, XA_subb, XA_cmp, XA_and, XA_or, XA_xor, XA_mov,
  };

  static enum nameNum xa_branches[] = {
	XA_bcc, XA_bcs, XA_bne, XA_beq, XA_bnv, XA_bov, XA_bpl, XA_bmi, XA_bg,
	XA_bl, XA_bge, XA_blt, XA_bgt, XA_ble, XA_br, XA_bkpt,
  };

  static enum nameNum xa_pushpop[] = {
	XA_push, XA_pushu, XA_pop, XA_popu,
  };

  static enum nameNum xa_bitops[] = {
	XA_clr, XA_setb, XA_mov, XA_mov, XA_anl, XA_anl, XA_orl, XA_orl,
  };

  static enum nameNum xa_Jxx[] = {
	XA_jb, XA_jnb, XA_jbc, XA_null,
  };

  static enum nameNum xa_misc[] = {
	XA_da, XA_sext, XA_cpl, XA_neg,
  };

  static enum nameNum xa_shifts[] = {
	XA_lsr, XA_asl, XA_asr, XA_norm,
  };

  ushort code = ua_next_byte();

  ushort nibble0 = (code & 0xF);
  ushort nibble1 = (code >> 4);
  signed char off;
  int size;
  ushort b1;

  if (nibble1 <= 0xB)
  {
    switch (nibble0 & 0x7)
    {
      case 0: // Specials
      case 7: // dtto
        switch (code)
        {
          case 0x00: // 00 - NOP
            cmd.itype = XA_nop;
            break;

          case 0x07: // PUSH.B Rlist
          case 0x0F: // PUSH.W Rlist
          case 0x17: // PUSHU.B Rlist
          case 0x1F: // PUSHU.W Rlist
          case 0x27: // POP.B Rlist
          case 0x2F: // POP.W Rlist
          case 0x37: // POPU.B Rlist
          case 0x3F: // POPU.W Rlist
          case 0x47: // PUSH.B Rlist
          case 0x4F: // PUSH.W Rlist
          case 0x57: // PUSHU.B Rlist
          case 0x5F: // PUSHU.W Rlist
          case 0x67: // POP.B Rlist
          case 0x6F: // POP.W Rlist
          case 0x77: // POPU.B Rlist
          case 0x7F: // POPU.W Rlist
            size = (nibble0 < 8) ? dt_byte : dt_word;
            b1 = ua_next_byte(); // Rlist
            cmd.itype = xa_pushpop[nibble1 & 3];
            if (nibble1 & 4) // High
              op_ph(cmd.Op1, fRlistH, b1, size);
            else
              op_ph(cmd.Op1, fRlistL, b1, size);
            break;

          case 0x08: // 08 - misc
            b1 = ua_next_byte();
            switch (b1 & 0xfc)
            {
              case 0x00: // CLR
              case 0x10: // SETB
                cmd.itype = xa_bitops[(b1>>4) & 7];
                op_bit(cmd.Op1, o_bit, ((b1&3)<<8) + (uchar)ua_next_byte());
                break;
              case 0x20: // MOV C,bit
                cmd.itype = xa_bitops[(b1>>4) & 7];
                opC(cmd.Op1);
                op_bit(cmd.Op2, o_bit, ((b1&3)<<8) + (uchar)ua_next_byte());
                break;
              case 0x30: // MOV bit,C
                cmd.itype = xa_bitops[(b1>>4) & 7];
                op_bit(cmd.Op1, o_bit, ((b1&3)<<8) + (uchar)ua_next_byte());
                opC(cmd.Op2);
                break;
              case 0x40: // ANL C, bit
              case 0x50: // ANL C, /bit
              case 0x60: // ORL C, bit
              case 0x70: // ORL C, /bit
                cmd.itype = xa_bitops[(b1>>4) & 7];
                opC(cmd.Op1);
                op_bit(cmd.Op2,
                  (b1&0x10)?o_bitnot:o_bit, ((b1&3)<<8) + (uchar)ua_next_byte());
                break;
              default: // undefined
                return 0;
            }
            break;

          case 0x40: // LEA
          case 0x48: // LEA
            cmd.itype = XA_lea;
            b1 = ua_next_byte();
            if (b1 & 0x88) return 0;
            op_rd(cmd.Op1, b1>>4, dt_word);
            if (code & 0x8) // 16bit offset
              op_ds(cmd.Op2, fRid16, b1&0x07, (long)ua_next_word_be(), dt_word);
            else
              op_ds(cmd.Op2, fRid8, b1&0x07, (signed char)ua_next_byte(), dt_word);
            break;

          case 0x50: // XCH.B Rd,[Rs]
          case 0x58: // XCH.W Rd,[Rs]
          case 0x60: // XCH.B Rd,Rs
          case 0x68: // XCH.W Rd,Rs
            cmd.itype = XA_xch;
            size = (nibble0 < 8) ? dt_byte : dt_word;
            b1 = ua_next_byte();
            op_rd(cmd.Op1, b1>>4, size);
            switch (nibble1)
            {
              case 0x5: // Rd,[Rs]
                if (b1 & 8) return 0;
                op_ds(cmd.Op2, fRi, b1&7, 0, size);
                break;
              case 0x6: // Rd,Rs
                op_rd(cmd.Op2, b1&0xf, size);
                break;
            }
            break;

          case 0x80: // MOVC
          case 0x88: // MOVC
            b1 = ua_next_byte();
            size = (nibble0 < 8) ? dt_byte : dt_word;
            if (b1 & 8) return 0;
            cmd.itype = XA_movc;
            op_rd(cmd.Op1, b1>>4, size);
            op_ph(cmd.Op2, fRip, b1&7, size);
            break;

          case 0x87: // DJNZ Rd, rel8
          case 0x8F: // POP, POPU, PUSH, PUSHU direct
            b1 = ua_next_byte();
            size = (nibble0 < 8) ? dt_byte : dt_word;
            if (b1 & 8) // DJNZ
            {
              if (b1 & 7) return 0;
              cmd.itype = XA_djnz;
              op_rd(cmd.Op1, b1>>4, size);
              op_rel(cmd.Op2, (signed char)ua_next_byte());
            } else { //POP, POPU, PUSH, PUSHU
              if (b1 & 0xc0) return 0;
              cmd.itype = xa_pushpop[3-((b1>>4)&3)];
              op_mm(cmd.Op1, ((b1 & 7) << 8) + ua_next_byte(), size);
            }
            break;

          case 0x90: // CPL, DA, SEXT
          case 0x98: // CPL & MOV [Rd+], [Rs+] & MOV direct, [Rs]
             b1 = ua_next_byte();
             size = (nibble0 < 8) ? dt_byte : dt_word;
             switch (b1 & 0x0f)
             {
               case 0x0: // MOV [Rd+], [Rs+]
               case 0x1:
               case 0x2:
               case 0x3:
               case 0x4:
               case 0x5:
               case 0x6:
               case 0x7: // MOV [Rd+], [Rs+]
                 if (b1 & 0x80) return 0;
                 cmd.itype = XA_mov;
                 op_ph(cmd.Op1, fRip, (b1>>4)&7, size);
                 op_ph(cmd.Op2, fRip, (b1&7), size);
                 break;

               case 0x8: // DA
               case 0x9: // SEXT
               case 0xA: // CPL
               case 0xB: // NEG
                 cmd.itype = xa_misc[b1&3];
                 op_rd(cmd.Op1, b1>>4, size);
                 if ((nibble0&8) && (cmd.itype==XA_da)) return 0;
                 break;

               case 0xC: // MOVC A,[A+PC] 904C
                 if ((nibble0 != 0) & ((b1&0xf0) != 0xc0)) return 0;
                 cmd.itype = XA_movc;
                 op_rd(cmd.Op1, rA, dt_byte);
                 op_ph(cmd.Op2, fApc, 0, dt_byte);
                 break;

               case 0xE: // MOVC A,[A+DPTR] 904E
                 if ((nibble0 != 0) & ((b1&0xf0) != 0xc0)) return 0;
                 cmd.itype = XA_movc;
                 op_rd(cmd.Op1, rA, dt_byte);
                 op_ph(cmd.Op2, fAdptr, 0, dt_byte);
                 break;

               case 0xF: // MOV Rd,USP & MOV USP, Rs
                 cmd.itype = XA_mov;
                 if (nibble0&8) // USP,Rs
                 {
                   op_rd(cmd.Op1, rUSP-rR0, dt_word);
                   op_rd(cmd.Op2, b1>>4, dt_word);
                 } else {
                   op_rd(cmd.Op1, b1>>4, dt_word);
                   op_rd(cmd.Op2, rUSP-rR0, dt_word);
                 }
                 break;

               default:
                 return 0;
             }
             break;

          case 0x97: // {JB,JBC,JNB} bit, rel8 & MOV direct, direct
          case 0x9F: // {JB,JBC,JNB} bit, rel8 & MOV direct, direct
             b1 = ua_next_byte();
             if ((b1 & 0x88) == 0x00) // MOV direct, direct
             {
               cmd.itype = XA_mov;
               size = (nibble0 < 8) ? dt_byte : dt_word;
               op_mm(cmd.Op1, ((b1 & 0x70) << 4) + (uchar)ua_next_byte(), size);
               op_mm(cmd.Op2, ((b1 & 0x7) << 8) + (uchar)ua_next_byte(), size);
             } else {
               if (nibble0 & 8) return 0;
               switch (b1 & 0xfc)
               {
                 case 0x80: // JB
                 case 0xA0: // JNB
                 case 0xC0: // JBC
                   cmd.itype = xa_Jxx[(b1>>5)&3];
                   op_bit(cmd.Op1, o_bit, ((b1&3)<<8) + (uchar)ua_next_byte());
                   op_rel(cmd.Op2, (signed char)ua_next_byte());
                   break;
                 default:
                   return 0;
               }
             }
             break;

          case 0xA0: // MOV.B direct, [Rs] & [Rd], direct & XCH
          case 0xA8: // MOV.W direct, [Rs] & [Rd], direct & XCH
            b1 = ua_next_byte();
            size = (nibble0 < 8) ? dt_byte : dt_word;
            if (b1 & 8) // XCH
            {
              cmd.itype = XA_xch;
              op_rd(cmd.Op1, b1>>4, size);
              op_mm(cmd.Op2, ((b1 & 7) << 8) + (uchar)ua_next_byte(), size);
            } else { // MOV
              cmd.itype = XA_mov;
              if (b1 & 0x80) // [Rd], direct
              {
                op_ds(cmd.Op1, fRi, (b1>>4)&7, 0, size);
                op_mm(cmd.Op2, ((b1 & 7) << 8) + (uchar)ua_next_byte(), size);
              } else {
                op_mm(cmd.Op1, ((b1 & 7) << 8) + (uchar)ua_next_byte(), size);
                op_ds(cmd.Op2, fRi, (b1>>4)&7, 0, size);
              }
            }
            break;

          case 0xA7: // MOVX
          case 0xAF: // MOVX
            cmd.itype = XA_movx;
            size = (nibble0 < 8) ? dt_byte : dt_word;
            b1 = ua_next_byte();
            if (b1 & 8) // [Rd],Rs
            {
              op_ds(cmd.Op1, fRi, b1&0x7, 0, size);
              op_rd(cmd.Op2, b1>>4, size);
            } else { // Rd,[Rs]
              op_rd(cmd.Op1, b1>>4, size);
              op_ds(cmd.Op2, fRi, b1&0x7, 0, size);
            }
            break;

          case 0xB0: // RR
          case 0xB7: // RRC
          case 0xB8: // RR
          case 0xBF: // RRC
            cmd.itype = (nibble0 & 7) ? XA_rrc : XA_rr;
            size = (nibble0 < 8) ? dt_byte : dt_word;
            b1 = ua_next_byte();
            op_rd(cmd.Op1, b1>>4, size);
            op_im(cmd.Op2, b1&0xf, size);
            break;

          default:
            return 0;
        }
        break;

      default:
        switch (nibble1)
        {
          case 0: // ADD
          case 1: // ADDC
          case 2: // SUB
          case 3: // SUBB
          case 4: // CMP
          case 5: // AND
          case 6: // OR
          case 7: // XOR
          case 8: // MOV
            cmd.itype = xa_basic[nibble1];
            size = (nibble0 < 8) ? dt_byte : dt_word;
            b1 = ua_next_byte();
            switch ( nibble0  & 0x7)
            {
              case 0x1: // OP Rd,Rs
                op_rd(cmd.Op1, b1>>4, size);
                op_rd(cmd.Op2, b1&0xF, size);
                break;

              case 0x2: // OP Rd,[Rs]
               if (b1 & 8) // [Rd], Rs
               {
                 op_ds(cmd.Op1, fRi, b1&7, 0, size);
                 op_rd(cmd.Op2, b1>>4, size);
               } else {
                 op_rd(cmd.Op1, b1>>4, size);
                 op_ds(cmd.Op2, fRi, b1&7, 0, size);
               }
               break;

             case 0x3: // OP Rd,[Rs+]
  	     if (b1 & 8) // [Rd], Rs
               {
                 op_ph(cmd.Op1, fRip, (b1&7), size);
                 op_rd(cmd.Op2, b1>>4, size);
               } else {
                 op_rd(cmd.Op1, b1>>4, size);
                 op_ph(cmd.Op2, fRip, (b1&7), size);
               }
               break;

             case 0x4: // OP Rd,[Rs+o8]
               if (b1 & 8) // [Rd], Rs
               {
                  op_ds(cmd.Op1, fRid8, (b1&7), (signed char)ua_next_byte(), size);
                  op_rd(cmd.Op2, b1>>4, size);
               } else {
                  op_rd(cmd.Op1, b1>>4, size);
                  op_ds(cmd.Op2, fRid8, (b1&7), (signed char)ua_next_byte(), size);
               }
               break;

             case 0x5: // OP Rd,[Rs+o16]
               if (b1 & 8) // [Rd], Rs
               {
                 op_ds(cmd.Op1, fRid16, (b1&7), (int)ua_next_word_be(), size);
  		 op_rd(cmd.Op2, b1>>4, size);
               } else {
                  op_rd(cmd.Op1, b1>>4, size);
                  op_ds(cmd.Op2, fRid16, (b1&7), (int)ua_next_word_be(), size);
               }
               break;

             case 0x6: // OP Rd,direct
               if (b1 & 8) // direct, Rs
               {
                 op_mm(cmd.Op1, ((b1 & 7) << 8) + ua_next_byte(), size);
                 op_rd(cmd.Op2, b1>>4, size);
               } else {
                 op_rd(cmd.Op1, b1>>4, size);
                 op_mm(cmd.Op2, ((b1 & 7) << 8) + ua_next_byte(), size);
               }
               break;
            }
            break;

          case 9: // Immediate operations
            b1 = ua_next_byte();
            cmd.itype = xa_basic[b1 & 0x0f];
            size = (nibble0 < 8) ? dt_byte : dt_word;
            switch (nibble0 & 0x7)
            {
              case 0x1:
                op_rd(cmd.Op1, b1>>4, size);
                op_im(cmd.Op2, (size == dt_byte) ? ua_next_byte() : ua_next_word_be(), size);
                break;

              case 0x2:
                op_ds(cmd.Op1, fRi, (b1>>4) & 0x7, 0, size);
                op_im(cmd.Op2, (size == dt_byte) ? ua_next_byte() : ua_next_word_be(), size);
                break;

              case 0x3:
                op_ph(cmd.Op1, fRip, (b1>>4) & 0x7, size);
                op_im(cmd.Op2, (size == dt_byte) ? ua_next_byte() : ua_next_word_be(), size);
                break;

              case 0x4:
                op_ds(cmd.Op1, fRid8, (b1>>4) & 0x7, (signed char)ua_next_byte(), size);
                op_im(cmd.Op2, (size == dt_byte) ? ua_next_byte() : ua_next_word_be(), size);
                break;

              case 0x5:
                op_ds(cmd.Op1, fRid16, (b1>>4) & 0x7, (int)ua_next_word_be(), size);
                op_im(cmd.Op2, (size == dt_byte) ? ua_next_byte() : ua_next_word_be(), size);
                break;

              case 0x6:
                op_mm(cmd.Op1, (((b1>>4) & 0x7) << 8) + ua_next_byte(), size);
                op_im(cmd.Op2, (size == dt_byte) ? ua_next_byte() : ua_next_word_be(), size);
                break;
            }
            break;

          case 0xA: // ADDS
          case 0xB: // MOVS
            b1 = ua_next_byte();
            cmd.itype = (nibble1 == 0x0A) ? XA_adds : XA_movs;
            size = (nibble0 < 8) ? dt_byte : dt_word;
            off = b1 & 0xf;
            if (off > 7)
            {
              off -= 16;
            }
            op_im(cmd.Op2, (long)off, size);
            switch (nibble0 & 0x7)
            {
              case 0x1:
                op_rd(cmd.Op1, b1>>4, size);
                break;

              case 0x2:
                op_ds(cmd.Op1, fRi, (b1>>4) & 0x7, 0, size);
                break;

              case 0x3:
                op_ph(cmd.Op1, fRip, (b1>>4) & 0x7, size);
                break;

              case 0x4:
                op_ds(cmd.Op1, fRid8, (b1>>4) & 0x7, (signed char)ua_next_byte(), size);
                break;

              case 0x5:
                op_ds(cmd.Op1, fRid16, (b1>>4) & 0x7, (int)ua_next_word_be(), size);
                break;

              case 0x6:
                op_mm(cmd.Op1, (((b1>>4) & 0x7) << 8) + (uchar)ua_next_byte(), size);
                break;
            }
            break;

        }
    }
  } else { // nibble1 > B
    switch (nibble1)
    {
      case 0xC: // Shifts, CALL, FCALL
        switch (nibble0 & 0xc)
        {
          case 0x0:
            size = dt_byte;
            break;
          case 0x8:
            size = dt_word;
            break;
          case 0xC:
            size = dt_dword;
            break;
          case 0x4: // Special instructions
            switch (nibble0)
            {
              case 4: // FCALL addr24
                cmd.itype = XA_fcall;
                cmd.Op1.type = o_far;
                cmd.Op1.dtyp = dt_code;
                cmd.Op1.addr = (ushort)ua_next_word_be();
                cmd.Op1.specval = (uchar)ua_next_byte();
                break;
              case 5: // CALL rel16
                cmd.itype = XA_call;
                op_rel(cmd.Op1, (int)ua_next_word_be());
                break;
              case 6: // CALL [Rs]
                b1 = ua_next_byte();
                if (b1 & 0xf8) return 0;
                cmd.itype = XA_call;
                op_ds(cmd.Op1, fRi, b1&7, 0, dt_word);
                break;
              default:
                return 0;
            }
            break;
        }
        if (cmd.itype == XA_null)
        {
          cmd.itype = xa_shifts[nibble0 & 3];
          b1 = ua_next_byte();
          op_rd(cmd.Op1, b1>>4, size);
          op_rd(cmd.Op2, b1&0xf, size);
        }
        break;

      case 0xD: // JMP, FJMP, rotations & shifts with #d4/#d5
        switch (nibble0 & 0xC)
        {
          case 0x4: // Special instructions
            switch (nibble0)
            {
              case 7: // rotate
                break;
              case 4: // FJMP addr24
                cmd.itype = XA_fjmp;
                cmd.Op1.type = o_far;
                cmd.Op1.dtyp = dt_code;
                cmd.Op1.addr = (ushort)ua_next_word_be();
                cmd.Op1.specval = (uchar)ua_next_byte();
                break;
              case 5: // JMP rel16
                cmd.itype = XA_jmp;
                op_rel(cmd.Op1, (int)ua_next_word_be());
                break;
              case 6: // specials
                cmd.itype = XA_jmp;
                b1 = ua_next_byte();
                switch (b1 & 0xf8)
                {
                  case 0x10: // RESET
                    if (b1 & 7) return 0;
                    cmd.itype = XA_reset;
                    break;
                  case 0x30: // TRAP
                  case 0x38: // TRAP
                    cmd.itype = XA_trap;
                    op_im(cmd.Op1, b1 & 0xf, dt_byte);
                    break;
                  case 0x40: // JMP [A+DPTR]
                    if ((b1&7) != 6) return 0;
                    op_ph(cmd.Op1, fAdptr, 0, dt_word);
                    break;
                  case 0x60: // JMP [[Rs+]]
                    op_ph(cmd.Op1, fRipi, b1&7, dt_word);
                    break;
                  case 0x70: // JMP [Rs]
                    op_ph(cmd.Op1, fRi, b1&7, dt_word);
                    break;
                  case 0x80: // RET
                    if (b1 & 7) return 0;
                    cmd.itype = XA_ret;
                    break;
                  case 0x90: // RETI
                    if (b1 & 7) return 0;
                    cmd.itype = XA_reti;
                    break;
                  default:
                    return 0;
                }
                break;
              default:
                return 0;
            }
            break;

          case 0x0:
            size = dt_byte;
            break;

          case 0x8:
            size = dt_word;
            break;

          case 0xC:
            size = dt_dword;
            break;
        }
        if (cmd.itype == XA_null)
        {
          cmd.itype = xa_shifts[nibble0 & 3];
          if (cmd.itype == XA_norm)
          { // rotations
            size = (nibble0 < 8) ? dt_byte : dt_word;
            cmd.itype = (nibble0 & 4) ? XA_rlc : XA_rl;
            b1 = ua_next_byte();
            op_rd(cmd.Op1, b1>>4, size);
            op_im(cmd.Op2, b1&0xf, size);
          } else { // shifts
            b1 = ua_next_byte();
            if (size == dt_dword)
            {
              op_rd(cmd.Op1, (b1>>4)&0x0e, size); // Only even registers allowed
              op_im(cmd.Op2, b1&0x1f, size);
            } else {
              op_rd(cmd.Op1, b1>>4, size);
              op_im(cmd.Op2, b1&0xf, size);
            }
          }
        }
        break;

      case 0xE: // DIV & MUL & cjne & jz/jnz
        b1 = ua_next_byte();
        switch (nibble0)
        {
          case 0x0: // MULU.B Rd,Rs
            cmd.itype = XA_mulu;
            op_rd(cmd.Op1, b1>>4, dt_byte);
            op_rd(cmd.Op2, b1&0xf, dt_byte);
            break;
          case 0x1: // DIVU.B Rd,Rs
            cmd.itype = XA_divu;
            op_rd(cmd.Op1, b1>>4, dt_byte);
            op_rd(cmd.Op2, b1&0xf, dt_byte);
            break;
          case 0x4: // MULU.W Rd,Rs
            cmd.itype = XA_mulu;
            op_rd(cmd.Op1, b1>>4, dt_word);
            op_rd(cmd.Op2, b1&0xf, dt_word);
            break;
          case 0x5: // DIVU.W Rd,Rs
            cmd.itype = XA_divu;
            op_rd(cmd.Op1, b1>>4, dt_word);
            op_rd(cmd.Op2, b1&0xf, dt_word);
            break;
          case 0x6: // MUL.W Rd,Rs
            cmd.itype = XA_mul;
            op_rd(cmd.Op1, b1>>4, dt_word);
            op_rd(cmd.Op2, b1&0xf, dt_word);
            break;
          case 0x7: // DIV.W Rd, Rs
            cmd.itype = XA_div;
            op_rd(cmd.Op1, b1>>4, dt_word);
            op_rd(cmd.Op2, b1&0xf, dt_word);
            break;
          case 0x8: // MUL & DIV Rd,#8
            switch (b1 & 0xf)
            {
              case 0x0: // MULU.B Rd,#d8
                cmd.itype = XA_mulu;
                size = dt_byte;
                break;
              case 0x1: // DIVU.B Rd,#d8
                cmd.itype = XA_divu;
                size = dt_byte;
                break;
              case 0x3: // DIVU.W Rd,#d8
                cmd.itype = XA_divu;
                size = dt_word;
                break;
              case 0xB: // DIV.W Rd,#d8
                cmd.itype = XA_div;
                size = dt_word;
                break;
              default:
                return 0;
            }
            op_rd(cmd.Op1, b1>>4, size);
            op_im(cmd.Op2, ua_next_byte(), dt_word);
            break;
          case 0x9: // MUL & DIV Rd,#16
            switch (b1 & 0xf)
            {
              case 0x0: // MULU.W Rd,#d16
                cmd.itype = XA_mulu;
                size = dt_word;
                break;
              case 0x1: // DIVU.D Rd,#d16
                if (b1&0x10) return 0;
                cmd.itype = XA_divu;
                size = dt_dword;
                break;
              case 0x8: // MUL.W Rd,#d16
                cmd.itype = XA_mul;
                size = dt_word;
                break;
              case 0x9: // DIV.D Rd,#d16
                if (b1&0x10) return 0;
                cmd.itype = XA_div;
                size = dt_dword;
                break;
              default:
                return 0;
            }
            op_rd(cmd.Op1, b1>>4, size);
            op_im(cmd.Op2, ua_next_word_be(), dt_byte);
            break;
          case 0xD: // DIVU.D Rd,Rs
            if (b1&0x10) return 0;
            cmd.itype = XA_divu;
            op_rd(cmd.Op1, b1>>4, dt_dword);
            op_rd(cmd.Op2, b1&0xf, dt_dword);
            break;
          case 0xF: // DIV.D Rd, Rs
            if (b1&0x10) return 0;
            cmd.itype = XA_div;
            op_rd(cmd.Op1, b1>>4, dt_dword);
            op_rd(cmd.Op2, b1&0xf, dt_dword);
            break;
          case 0x2: // cjne direct & [Rd] & DJNZ direct
          case 0xA: // cjne direct & [Rd] & DJNZ direct
            size = (nibble0 < 8) ? dt_byte : dt_word;
            if (b1 & 8)
            { // DJNZ direct, rel8
              cmd.itype = XA_djnz;
              op_mm(cmd.Op1, ((b1&7)<<8)+(uchar)ua_next_byte(), size);
              op_rel(cmd.Op2, (signed char)ua_next_byte());
            } else { // CJNE.s Rd, direct, rel8
              cmd.itype = XA_cjne;
              op_rd(cmd.Op1, b1>>4, size);
              op_mm(cmd.Op2, ((b1&7)<<8)+(uchar)ua_next_byte(), size);
              op_rel(cmd.Op3, (signed char)ua_next_byte());
            }
            break;
          case 0x3: // cjne #,rel
          case 0xB: // cjne #,rel
            if (b1 & 7) return 0;
            cmd.itype = XA_cjne;
            size = (nibble0 < 8) ? dt_byte : dt_word;
            off = ua_next_byte();
            if (b1 & 0x8)
            {
              op_ds(cmd.Op1, fRi, b1>>4, 0, size);
            } else {
              op_rd(cmd.Op1, b1>>4, size);
            }
            op_im(cmd.Op2, (size==dt_byte)?ua_next_byte():ua_next_word_be(), size);
            op_rel(cmd.Op3, off);
            break;
          case 0xC: // JZ rel8
            cmd.itype = XA_jz;
            op_rel(cmd.Op1, (signed char)ua_next_byte());
            break;
          case 0xE: // JNZ rel8
            cmd.itype = XA_jnz;
            op_rel(cmd.Op1, (signed char)ua_next_byte());
            break;
          default:
            return 0;
        }
        break;

      case 0xF: // Bxx
        cmd.itype = xa_branches[nibble0];
        if (nibble0 != 0xF)
        {
          op_rel(cmd.Op1, (signed char)ua_next_byte());
        }
        break;
    }
  }
  return cmd.size;
}

//----------------------------------------------------------------------
// analyze an instruction
int ana(void)
{
  cmd.itype = XA_null;
  cmd.Op1.dtyp = dt_byte;
  cmd.Op2.dtyp = dt_byte;
  cmd.Op3.dtyp = dt_byte;

  switch ( ptype )
  {
    case prc_xaG3:
      return ana_basic();
  }
  return 0;
}