CRC.cpp

/*
*   Glide64 - Glide video plugin for Nintendo 64 emulators.
*   Copyright (c) 2002  Dave2001
*
*   This program is free software; you can redistribute it and/or modify
*   it under the terms of the GNU General Public License as published by
*   the Free Software Foundation; either version 2 of the License, or
*   any later version.
*
*   This program is distributed in the hope that it will be useful,
*   but WITHOUT ANY WARRANTY; without even the implied warranty of
*   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*   GNU General Public License for more details.
*
*   You should have received a copy of the GNU General Public
*   Licence along with this program; if not, write to the Free
*   Software Foundation, Inc., 51 Franklin Street, Fifth Floor, 
*   Boston, MA  02110-1301, USA
*/

//****************************************************************
//
// Glide64 - Glide Plugin for Nintendo 64 emulators (tested mostly with Project64)
// Project started on December 29th, 2001
//
// To modify Glide64:
// * 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.
// * 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.
//
// Official Glide64 development channel: #Glide64 on EFnet
//
// Original author: Dave2001 ([email protected])
// Other authors: Gonetz, Gugaman
//
//****************************************************************
//
// CRC32 calculation functions 
//
// Created by Gonetz, 2004
//
//****************************************************************

#include "CRC.h"

#define CRC32_POLYNOMIAL     0x04C11DB7

unsigned int CRCTable[ 256 ];

unsigned int Reflect( unsigned long ref, char ch )
{
     unsigned int value = 0;

     // Swap bit 0 for bit 7
     // bit 1 for bit 6, etc.
     for (char i = 1; i < (ch + 1); i++)
     {
          if(ref & 1)
               value |= 1 << (ch - i);
          ref >>= 1;
     }
     return value;
}

void CRC_BuildTable()
{
    unsigned int crc;

    for (unsigned i = 0; i <= 255; i++)
    {
        crc = Reflect( i, 8 ) << 24;
        for (unsigned j = 0; j < 8; j++)
            crc = (crc << 1) ^ (crc & (1 << 31) ? CRC32_POLYNOMIAL : 0);
        
        CRCTable[i] = Reflect( crc, 32 );
    }
}