crc32.cpp

#include <stdint.h>
#include <stdio.h>
#include <string.h>


#define UPDC32(octet, crc) (crc_32_tab[((crc >> 24 ) ^ (octet)) & 0xff] ^ ((crc) << 8))


static uint32_t crc_32_tab[] = { /* CRC polynomial 0xedb88320 */
    			0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9,
    			0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
    			0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
    			0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd,
    			0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9,
    			0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
    			0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011,
    			0x791d4014, 0x7ddc5da3, 0x709f7b7a, 0x745e66cd,
    			0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
    			0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
    			0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81,
    			0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
    			0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49,
    			0xc7361b4c, 0xc3f706fb, 0xceb42022, 0xca753d95,
    			0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
    			0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d,
    			0x34867077, 0x30476dc0, 0x3d044b19, 0x39c556ae,
    			0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
    			0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16,
    			0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
    			0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde,
    			0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02,
    			0x5e9f46bf, 0x5a5e5b08, 0x571d7dd1, 0x53dc6066,
    			0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
    			0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e,
    			0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692,
    			0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6,
    			0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a,
    			0xe0b41de7, 0xe4750050, 0xe9362689, 0xedf73b3e,
    			0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
    			0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686,
    			0xd5b88683, 0xd1799b34, 0xdc3abded, 0xd8fba05a,
    			0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637,
    			0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb,
    			0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f,
    			0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
    			0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47,
    			0x36194d42, 0x32d850f5, 0x3f9b762c, 0x3b5a6b9b,
    			0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff,
    			0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
    			0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7,
    			0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
    			0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f,
    			0xc423cd6a, 0xc0e2d0dd, 0xcda1f604, 0xc960ebb3,
    			0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
    			0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b,
    			0x9b3660c6, 0x9ff77d71, 0x92b45ba8, 0x9675461f,
    			0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
    			0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640,
    			0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
    			0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8,
    			0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24,
    			0x119b4be9, 0x155a565e, 0x18197087, 0x1cd86d30,
    			0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
    			0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088,
    			0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654,
    			0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0,
    			0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c,
    			0xe3a1cbc1, 0xe760d676, 0xea23f0af, 0xeee2ed18,
    			0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
    			0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0,
    			0x9abc8bd5, 0x9e7d9662, 0x933eb0bb, 0x97ffad0c,
    			0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668,
    			0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4
    	
};


uint32_t crc32buf(const char *buf, size_t len)
{
      register uint32_t oldcrc32;

      oldcrc32 = 0xFFFFFFFF;

      for ( ; len; --len, ++buf)
      {
            oldcrc32 = UPDC32(*buf, oldcrc32);
      }

      return ~oldcrc32;
      
}

uint32_t crc32str(const char *buf)
{
	return crc32buf(buf, strlen(buf));
}



#define FINAL 0xffffffff


uint32_t find_old_crc(uint32_t current_crc, char removed)
{
	int i,j;
	current_crc ^= FINAL;

	for(i=0; i < 256; i++) {
		uint32_t xx = current_crc ^ crc_32_tab[i]; 	
		xx = xx >> 8;
		for(j=0; j<256; j++) {
			uint32_t _oldcrc = xx | (j<<24);
			uint32_t nextcrc = UPDC32(removed, _oldcrc);
			if (nextcrc==current_crc) {
				//printf("Found oldCRC = %08x\n", _oldcrc ^ FINAL);
				return _oldcrc ^ FINAL;
			}
		}

	}

}

uint32_t compute_removed_crc(const char *s, char c)
{
	uint32_t x = crc32str(s);
	return find_old_crc(x, c);	
}

uint32_t compute_removed_str(const char *s, const char *s2)
{
	int x = strlen(s2)-1;
	uint32_t now = crc32str(s);
	while (x>=0) {
		now = find_old_crc(now, s2[x]);
		x--;
	}
	return now;

}

uint32_t compute_removed_str2(uint32_t oldhash, const char *s2)
{
	int x = strlen(s2)-1;
	uint32_t now = oldhash;
	while (x>=0) {
		now = find_old_crc(now, s2[x]);
		x--;
	}
	return now;

}


uint32_t endian(uint32_t num) {
return ((num>>24)&0xff) | // move byte 3 to byte 0
                    ((num<<8)&0xff0000) | // move byte 1 to byte 2
                    ((num>>8)&0xff00) | // move byte 2 to byte 1
                    ((num<<24)&0xff000000); // byte 0 to byte 3
}

int main(int argc, char *argv[])
{
	uint32_t x = crc32str("Admin"); 
	printf("Admin %08x\n", endian(x));
	
	printf("%08x \n", endian(compute_removed_crc("AdminX", 'X')));
	printf("%08x \n", endian(compute_removed_str("AdminXY", "XY")));
	uint32_t x3 = (compute_removed_str2(endian(0xe09847e1), "J"));
	printf("%08x \n", endian(x3));
	
}