



/*
   CRC-32
   Copyright (C) 1995-1998 Mark Adler
*/

#define CRC32_INIT_VALUE	0xffffffffL
#define CRC32_XOR_VALUE		0xffffffffL

#ifdef CREATE_CRC_TABLE

static unsigned long crctable[256];

/*
   Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
   x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x^1+x^0.

   Polynomials over GF(2) are represented in binary, one bit per coefficient,
   with the lowest powers in the most significant bit.  Then adding polynomials
   is just exclusive-or, and multiplying a polynomial by x is a right shift by
   one.  If we call the above polynomial p, and represent a byte as the
   polynomial q, also with the lowest power in the most significant bit (so the
   byte 0xb1 is the polynomial x^7+x^3+x^1+x^0), then the CRC is (q*x^32) mod p,
   where a mod b means the remainder after dividing a by b.

   This calculation is done using the shift-register method of multiplying and
   taking the remainder.  The register is initialized to zero, and for each
   incoming bit, x^32 is added mod p to the register if the bit is a one (where
   x^32 mod p is p+x^32 = x^26+...+x^0), and the register is multiplied mod p by
   x (which is shifting right by one and adding x^32 mod p if the bit shifted
   out is a one).  We start with the highest power (least significant bit) of
   q and repeat for all eight bits of q.

   The table is simply the CRC of all possible eight bit values. This is all
   the information needed to generate CRC's on data a byte at a time for all
   combinations of CRC register values and incoming bytes.
*/

void make_crc_table( void ) {
	int i, j;
	unsigned long c, poly;
	/* terms of polynomial defining this crc (except x^32): */
	static const byte p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};

	/* make exclusive-or pattern from polynomial (0xedb88320L) */
	poly = 0L;
	for ( i = 0; i < sizeof( p ) / sizeof( byte ); i++ ) {
		poly |= 1L << ( 31 - p[i] );
	}

	for ( i = 0; i < 256; i++ ) {
		c = (unsigned long)i;
		for ( j = 0; j < 8; j++ ) {
			c = ( c & 1 ) ? poly ^ ( c >> 1 ) : ( c >> 1 );
		}
		crctable[i] = c;
	}
}

#else

/*
  Table of CRC-32's of all single-byte values (made by make_crc_table)
*/
static unsigned long crctable[256] = {
	0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL,
	0x076dc419L, 0x706af48fL, 0xe963a535L, 0x9e6495a3L,
	0x0edb8832L, 0x79dcb8a4L, 0xe0d5e91eL, 0x97d2d988L,
	0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L, 0x90bf1d91L,
	0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
	0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L,
	0x136c9856L, 0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL,
	0x14015c4fL, 0x63066cd9L, 0xfa0f3d63L, 0x8d080df5L,
	0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L, 0xa2677172L,
	0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
	0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L,
	0x32d86ce3L, 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L,
	0x26d930acL, 0x51de003aL, 0xc8d75180L, 0xbfd06116L,
	0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, 0xb8bda50fL,
	0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
	0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL,
	0x76dc4190L, 0x01db7106L, 0x98d220bcL, 0xefd5102aL,
	0x71b18589L, 0x06b6b51fL, 0x9fbfe4a5L, 0xe8b8d433L,
	0x7807c9a2L, 0x0f00f934L, 0x9609a88eL, 0xe10e9818L,
	0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
	0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL,
	0x6c0695edL, 0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L,
	0x65b0d9c6L, 0x12b7e950L, 0x8bbeb8eaL, 0xfcb9887cL,
	0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L, 0xfbd44c65L,
	0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
	0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL,
	0x4369e96aL, 0x346ed9fcL, 0xad678846L, 0xda60b8d0L,
	0x44042d73L, 0x33031de5L, 0xaa0a4c5fL, 0xdd0d7cc9L,
	0x5005713cL, 0x270241aaL, 0xbe0b1010L, 0xc90c2086L,
	0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
	0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L,
	0x59b33d17L, 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL,
	0xedb88320L, 0x9abfb3b6L, 0x03b6e20cL, 0x74b1d29aL,
	0xead54739L, 0x9dd277afL, 0x04db2615L, 0x73dc1683L,
	0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
	0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L,
	0xf00f9344L, 0x8708a3d2L, 0x1e01f268L, 0x6906c2feL,
	0xf762575dL, 0x806567cbL, 0x196c3671L, 0x6e6b06e7L,
	0xfed41b76L, 0x89d32be0L, 0x10da7a5aL, 0x67dd4accL,
	0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
	0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L,
	0xd1bb67f1L, 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL,
	0xd80d2bdaL, 0xaf0a1b4cL, 0x36034af6L, 0x41047a60L,
	0xdf60efc3L, 0xa867df55L, 0x316e8eefL, 0x4669be79L,
	0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
	0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL,
	0xc5ba3bbeL, 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L,
	0xc2d7ffa7L, 0xb5d0cf31L, 0x2cd99e8bL, 0x5bdeae1dL,
	0x9b64c2b0L, 0xec63f226L, 0x756aa39cL, 0x026d930aL,
	0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
	0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L,
	0x92d28e9bL, 0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L,
	0x86d3d2d4L, 0xf1d4e242L, 0x68ddb3f8L, 0x1fda836eL,
	0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L, 0x18b74777L,
	0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
	0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L,
	0xa00ae278L, 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L,
	0xa7672661L, 0xd06016f7L, 0x4969474dL, 0x3e6e77dbL,
	0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, 0x37d83bf0L,
	0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
	0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L,
	0xbad03605L, 0xcdd70693L, 0x54de5729L, 0x23d967bfL,
	0xb3667a2eL, 0xc4614ab8L, 0x5d681b02L, 0x2a6f2b94L,
	0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL, 0x2d02ef8dL
};

#endif

void CRC32_InitChecksum( unsigned long &crcvalue ) {
	crcvalue = CRC32_INIT_VALUE;
}

void CRC32_Update( unsigned long &crcvalue, const byte data ) {
	crcvalue = crctable[ ( crcvalue ^ data ) & 0xff ] ^ ( crcvalue >> 8 );
}

void CRC32_UpdateChecksum( unsigned long &crcvalue, const void *data, int length ) {
	unsigned long crc;
	const unsigned char *buf = (const unsigned char *) data;

	crc = crcvalue;
	while( length-- ) {
		crc = crctable[ ( crc ^ ( *buf++ ) ) & 0xff ] ^ ( crc >> 8 );
	}
	crcvalue = crc;
}

void CRC32_FinishChecksum( unsigned long &crcvalue ) {
	crcvalue ^= CRC32_XOR_VALUE;
}

unsigned long CRC32_BlockChecksum( const void *data, int length ) {
	unsigned long crc;

	CRC32_InitChecksum( crc );
	CRC32_UpdateChecksum( crc, data, length );
	CRC32_FinishChecksum( crc );
	return crc;
}
