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      1 /*
      2  * CRC32 using the polynomial from IEEE-802.3
      3  *
      4  * Authors: Lasse Collin <lasse.collin (at) tukaani.org>
      5  *          Igor Pavlov <http://7-zip.org/>
      6  *
      7  * This file has been put into the public domain.
      8  * You can do whatever you want with this file.
      9  */
     10 
     11 /*
     12  * This is not the fastest implementation, but it is pretty compact.
     13  * The fastest versions of xz_crc32() on modern CPUs without hardware
     14  * accelerated CRC instruction are 3-5 times as fast as this version,
     15  * but they are bigger and use more memory for the lookup table.
     16  */
     17 
     18 #include "xz_private.h"
     19 
     20 /*
     21  * STATIC_RW_DATA is used in the pre-boot environment on some architectures.
     22  * See <linux/decompress/mm.h> for details.
     23  */
     24 #ifndef STATIC_RW_DATA
     25 #	define STATIC_RW_DATA static
     26 #endif
     27 
     28 STATIC_RW_DATA uint32_t xz_crc32_table[256];
     29 
     30 XZ_EXTERN void xz_crc32_init(void)
     31 {
     32 	const uint32_t poly = 0xEDB88320;
     33 
     34 	uint32_t i;
     35 	uint32_t j;
     36 	uint32_t r;
     37 
     38 	for (i = 0; i < 256; ++i) {
     39 		r = i;
     40 		for (j = 0; j < 8; ++j)
     41 			r = (r >> 1) ^ (poly & ~((r & 1) - 1));
     42 
     43 		xz_crc32_table[i] = r;
     44 	}
     45 
     46 	return;
     47 }
     48 
     49 XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
     50 {
     51 	crc = ~crc;
     52 
     53 	while (size != 0) {
     54 		crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
     55 		--size;
     56 	}
     57 
     58 	return ~crc;
     59 }
     60