#include <Shared/Shrink.h>

// Original source: http://hack-expo.void.ru/groups/blt/text/disasm.txt

// disasm_flag values:
#define C_66           0x00000001       // 66-prefix
#define C_67           0x00000002       // 67-prefix
#define C_LOCK         0x00000004       // lock
#define C_REP          0x00000008       // repz/repnz
#define C_SEG          0x00000010       // seg-prefix
#define C_OPCODE2      0x00000020       // 2nd opcode present (1st==0F)
#define C_MODRM        0x00000040       // modrm present
#define C_SIB          0x00000080       // sib present
#define C_ANYPREFIX    (C_66|C_67|C_LOCK|C_REP|C_SEG)

DWORD disasm_len;                       // 0 if error
DWORD disasm_flag;                      // C_xxx
DWORD disasm_memsize;                   // value = disasm_mem
DWORD disasm_datasize;                  // value = disasm_data
DWORD disasm_defdata;                   // == C_66 ? 2 : 4
DWORD disasm_defmem;                    // == C_67 ? 2 : 4

BYTE  disasm_seg;                       // CS DS ES SS FS GS
BYTE  disasm_rep;                       // REPZ/REPNZ
BYTE  disasm_opcode;                    // opcode
BYTE  disasm_opcode2;                   // used when opcode==0F
BYTE  disasm_modrm;                     // modxxxrm
BYTE  disasm_sib;                       // scale-index-base
BYTE  disasm_mem[8];                    // mem addr value
BYTE  disasm_data[8];                   // data value

// returns: length if success
//          0 if error

int disasm(BYTE* opcode0)
{
  BYTE* opcode = opcode0;

  disasm_len = 0;
  disasm_flag = 0;
  disasm_datasize = 0;
  disasm_memsize = 0;
  disasm_defdata = 4;
  disasm_defmem = 4;

retry:
  disasm_opcode = *opcode++;

  switch (disasm_opcode)
  {
    case 0x00: case 0x01: case 0x02: case 0x03:
    case 0x08: case 0x09: case 0x0A: case 0x0B:
    case 0x10: case 0x11: case 0x12: case 0x13:
    case 0x18: case 0x19: case 0x1A: case 0x1B:
    case 0x20: case 0x21: case 0x22: case 0x23:
    case 0x28: case 0x29: case 0x2A: case 0x2B:
    case 0x30: case 0x31: case 0x32: case 0x33:
    case 0x38: case 0x39: case 0x3A: case 0x3B:
    case 0x62: case 0x63:
    case 0x84: case 0x85: case 0x86: case 0x87:
    case 0x88: case 0x89: case 0x8A: case 0x8B:
    case 0x8C: case 0x8D: case 0x8E: case 0x8F:
    case 0xC4: case 0xC5:
    case 0xD0: case 0xD1: case 0xD2: case 0xD3:
    case 0xD8: case 0xD9: case 0xDA: case 0xDB:
    case 0xDC: case 0xDD: case 0xDE: case 0xDF:
    case 0xFE: case 0xFF:
               disasm_flag |= C_MODRM;
               break;
    case 0xCD: disasm_datasize += *opcode==0x20 ? 1+4 : 1;
               break;
    case 0xF6:
    case 0xF7: disasm_flag |= C_MODRM;
               if (*opcode & 0x38) break;
               // continue if <test ..., xx>
    case 0x04: case 0x05: case 0x0C: case 0x0D:
    case 0x14: case 0x15: case 0x1C: case 0x1D:
    case 0x24: case 0x25: case 0x2C: case 0x2D:
    case 0x34: case 0x35: case 0x3C: case 0x3D:
               if (disasm_opcode & 1)
                 disasm_datasize += disasm_defdata;
               else
                 disasm_datasize++;
               break;
    case 0x6A:
    case 0xA8:
    case 0xB0: case 0xB1: case 0xB2: case 0xB3:
    case 0xB4: case 0xB5: case 0xB6: case 0xB7:
    case 0xD4: case 0xD5:
    case 0xE4: case 0xE5: case 0xE6: case 0xE7:
    case 0x70: case 0x71: case 0x72: case 0x73:
    case 0x74: case 0x75: case 0x76: case 0x77:
    case 0x78: case 0x79: case 0x7A: case 0x7B:
    case 0x7C: case 0x7D: case 0x7E: case 0x7F:
    case 0xEB:
    case 0xE0: case 0xE1: case 0xE2: case 0xE3:
               disasm_datasize++;
               break;
    case 0x26: case 0x2E: case 0x36: case 0x3E:
    case 0x64: case 0x65:
               if (disasm_flag & C_SEG) return 0;
               disasm_flag |= C_SEG;
               disasm_seg = disasm_opcode;
               goto retry;
    case 0xF0:
               if (disasm_flag & C_LOCK) return 0;
               disasm_flag |= C_LOCK;
               goto retry;
    case 0xF2: case 0xF3:
               if (disasm_flag & C_REP) return 0;
               disasm_flag |= C_REP;
               disasm_rep = disasm_opcode;
               goto retry;
    case 0x66:
               if (disasm_flag & C_66) return 0;
               disasm_flag |= C_66;
               disasm_defdata = 2;
               goto retry;
    case 0x67:
               if (disasm_flag & C_67) return 0;
               disasm_flag |= C_67;
               disasm_defmem = 2;
               goto retry;
    case 0x6B:
    case 0x80:
    case 0x82:
    case 0x83:
    case 0xC0:
    case 0xC1:
    case 0xC6: disasm_datasize++;
               disasm_flag |= C_MODRM;
               break;
    case 0x69:
    case 0x81:
    case 0xC7:
               disasm_datasize += disasm_defdata;
               disasm_flag |= C_MODRM;
               break;
    case 0x9A:
    case 0xEA: disasm_datasize += 2 + disasm_defdata;
               break;
    case 0xA0:
    case 0xA1:
    case 0xA2:
    case 0xA3: disasm_memsize += disasm_defmem;
               break;
    case 0x68:
    case 0xA9:
    case 0xB8: case 0xB9: case 0xBA: case 0xBB:
    case 0xBC: case 0xBD: case 0xBE: case 0xBF:
    case 0xE8:
    case 0xE9:
               disasm_datasize += disasm_defdata;
               break;
    case 0xC2:
    case 0xCA: disasm_datasize += 2;
               break;
    case 0xC8:
               disasm_datasize += 3;
               break;
    case 0xF1:
               return 0;
    case 0x0F:
      disasm_flag |= C_OPCODE2;
      disasm_opcode2 = *opcode++;
      switch (disasm_opcode2)
      {
        case 0x00: case 0x01: case 0x02: case 0x03:
        case 0x90: case 0x91: case 0x92: case 0x93:
        case 0x94: case 0x95: case 0x96: case 0x97:
        case 0x98: case 0x99: case 0x9A: case 0x9B:
        case 0x9C: case 0x9D: case 0x9E: case 0x9F:
        case 0xA3:
        case 0xA5:
        case 0xAB:
        case 0xAD:
        case 0xAF:
        case 0xB0: case 0xB1: case 0xB2: case 0xB3:
        case 0xB4: case 0xB5: case 0xB6: case 0xB7:
        case 0xBB:
        case 0xBC: case 0xBD: case 0xBE: case 0xBF:
        case 0xC0:
        case 0xC1:
                   disasm_flag |= C_MODRM;
                   break;
        case 0x06:
        case 0x08: case 0x09: case 0x0A: case 0x0B:
        case 0xA0: case 0xA1: case 0xA2: case 0xA8:
        case 0xA9:
        case 0xAA:
        case 0xC8: case 0xC9: case 0xCA: case 0xCB:
        case 0xCC: case 0xCD: case 0xCE: case 0xCF:
                   break;
        case 0x80: case 0x81: case 0x82: case 0x83:
        case 0x84: case 0x85: case 0x86: case 0x87:
        case 0x88: case 0x89: case 0x8A: case 0x8B:
        case 0x8C: case 0x8D: case 0x8E: case 0x8F:
                   disasm_datasize += disasm_defdata;
                   break;
        case 0xA4:
        case 0xAC:
        case 0xBA:
                   disasm_datasize++;
                   disasm_flag |= C_MODRM;
                   break;
        default:
                   return 0;
      } // 0F-switch
      break;

  } //switch

  if (disasm_flag & C_MODRM)
  {
    disasm_modrm = *opcode++;
    BYTE mod = disasm_modrm & 0xC0;
    BYTE rm  = disasm_modrm & 0x07;
    if (mod != 0xC0)
    {
      if (mod == 0x40) disasm_memsize++;
      if (mod == 0x80) disasm_memsize += disasm_defmem;
      if (disasm_defmem == 2)           // modrm16
      {
        if ((mod == 0x00)&&(rm == 0x06)) disasm_memsize+=2;
      }
      else                              // modrm32
      {
        if (rm==0x04)
        {
          disasm_flag |= C_SIB;
          disasm_sib = *opcode++;
          rm = disasm_sib & 0x07;
        }
        if ((rm==0x05)&&(mod==0x00)) disasm_memsize+=4;
      }
    }
  } // C_MODRM

  for(DWORD i=0; i<disasm_memsize; i++)
    disasm_mem[i] = *opcode++;
  for(DWORD i=0; i<disasm_datasize; i++)
    disasm_data[i] = *opcode++;

  disasm_len = opcode - opcode0;

  return disasm_len;
} //disasm
