CRC.h

   1 /*
   2 *       Glide64 - Glide video plugin for Nintendo 64 emulators.
   3 *       Copyright (c) 2002  Dave2001
   4 *       Copyright (c) 2008  Günther <guenther.emu@freenet.de>
   5 *
   6 *       This program is free software; you can redistribute it and/or modify
   7 *       it under the terms of the GNU General Public License as published by
   8 *       the Free Software Foundation; either version 2 of the License, or
   9 *       any later version.
  10 *
  11 *       This program is distributed in the hope that it will be useful,
  12 *       but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 *       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 *       GNU General Public License for more details.
  15 *
  16 *       You should have received a copy of the GNU General Public License
  17 *       along with this program; if not, write to the Free Software
  18 *       Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  19 */
  20
  21 //****************************************************************
  22 //
  23 // Glide64 - Glide Plugin for Nintendo 64 emulators (tested mostly with Project64)
  24 // Project started on December 29th, 2001
  25 //
  26 // To modify Glide64:
  27 // * Write your name and (optional)email, commented by your work, so I know who did it, and so that you can find which parts you modified when it comes time to send it to me.
  28 // * Do NOT send me the whole project or file that you modified.  Take out your modified code sections, and tell me where to put them.  If people sent the whole thing, I would have many different versions, but no idea how to combine them all.
  29 //
  30 // Official Glide64 development channel: #Glide64 on EFnet
  31 //
  32 // Original author: Dave2001 (Dave2999@hotmail.com)
  33 // Other authors: Gonetz, Gugaman
  34 //
  35 //****************************************************************
  36 //
  37 // CRC32 calculation functions
  38 //
  39 // Created by Gonetz, 2004
  40 //
  41 //****************************************************************
  42
  43 #if !defined(WIN32) && defined(GCC)
  44 #define Crc32 _Crc32
  45 #define CRCTable _CRCTable
  46 #endif
  47
  48 extern unsigned int CRCTable[ 256 ];
  49
  50 void CRC_BuildTable();
  51
  52 inline unsigned int CRC_Calculate( unsigned int crc, const void *buffer, unsigned int count )
  53 {
  54 #ifndef GCC
  55   unsigned int Crc32=crc;
  56   __asm {
  57                         mov     esi, buffer
  58                         mov     edx, count
  59                         add     edx, esi
  60                         mov     ecx, crc
  61
  62 loop1:
  63                         mov     bl, byte ptr [esi]
  64                         movzx   eax, cl
  65                         inc     esi
  66                         xor     al, bl
  67                         shr     ecx, 8
  68                         mov     ebx, [CRCTable+eax*4]
  69                         xor     ecx, ebx
  70
  71                         cmp     edx, esi
  72                         jne     loop1
  73
  74                         xor     Crc32, ecx
  75    }
  76    return Crc32;
  77 #else // _WIN32
  78     unsigned int result = crc;
  79     for (const char * p = (const char*)buffer; p != (const char*)buffer + count; ++p)
  80     {
  81         unsigned char al = result;
  82         al ^= *p;
  83         result >>= 8;
  84         result ^= CRCTable[al];
  85     }
  86     result ^= crc;
  87     return result;
  88 #endif // _WIN32
  89 }
  90