Fix CRC32_Compute

[ResurrectedTrader]

Three bugs made CRC32_Compute differ from the game's:

• sgCrc32LookupTable[1] was written in decimal (77073096, i.e. 0x04980AC8) instead of 0x77073096.
• The table index was not masked to a byte, so nCRC32 ^ nByte indexed far past the 256-entry table.
• The final complement was missing.

The game's function is plain CRC-32: all 256 entries of its table are the standard (0xEDB88320) table, which MOO's table matches apart from entry 1, and its output equals zlib's crc32.

1.10f

D2Game.0x6FD269D3, Hex-Rays:

int __fastcall sub_6FD269D3(unsigned __int8 *a1, int a2)
{
  unsigned int v2; // eax

  if ( a2 == 0 )
  {
    Fog_10023(aDwsize, aCProjectsD2Hea_47, 64);
    exit(-1);
  }
  v2 = 0xFFFFFFFF;
  do
  {
    v2 = dword_6FD2A248[(unsigned __int8)v2 ^ *a1++] ^ (v2 >> 8);   // <== byte index
    --a2;
  }
  while ( a2 != 0 );
  return ~v2;                                                       // <== complement
}

6FD269F2  push    esi
6FD269F3  or      eax, 0FFFFFFFFh
6FD269F6  push    edi
6FD269F7  movzx   esi, byte ptr [ecx]
6FD269FA  movzx   edi, al                           ; <== low byte only
6FD269FD  xor     esi, edi
6FD269FF  shr     eax, 8
6FD26A02  mov     esi, [esi*4+6FD2A248h]
6FD26A09  xor     eax, esi
6FD26A0B  inc     ecx
6FD26A0C  dec     edx
6FD26A0D  jnz     6FD269F7
6FD26A0F  pop     edi
6FD26A10  pop     esi
6FD26A11  not     eax                               ; <== final complement
6FD26A13  retn

The table at 0x6FD2A248 starts 00000000 77073096 EE0E612C 990951BA.

The only caller, D2GAME_SAVE_CalculateChecksum_6FC8A140, returns the value unchanged:

result = sub_6FD269D3((unsigned __int8 *)a1, a2);
...
return result;

1.14d

D2HELL_CRC32_Compute (Game.exe 0x006C99F6, table 0x006FD3E8) is identical:

v2 = 0xFFFFFFFF;
do
{
  v2 = dword_6FD3E8[(unsigned __int8)v2 ^ *a1] ^ (v2 >> 8);
  --a2;
  ++a1;
}
while ( a2 != 0 );
return ~v2;

Change

Fix table entry 1, mask the index with & 0xFF, return ~nCRC32, and use size_t for the loop index. Not version-gated, since 1.10f and 1.14d agree. Also adds the 1.14d address.

🤖 Generated with Claude Code