lib/xz/xz_crc32.c

24fa0402SLasse Collin/*
24fa0402SLasse Collin * CRC32 using the polynomial from IEEE-802.3
24fa0402SLasse Collin *
24fa0402SLasse Collin * Authors: Lasse Collin <lasse.collin@tukaani.org>
d89775fcSAlexander A. Klimov *          Igor Pavlov <https://7-zip.org/>
24fa0402SLasse Collin *
24fa0402SLasse Collin * This file has been put into the public domain.
24fa0402SLasse Collin * You can do whatever you want with this file.
24fa0402SLasse Collin */
24fa0402SLasse Collin
24fa0402SLasse Collin/*
24fa0402SLasse Collin * This is not the fastest implementation, but it is pretty compact.
24fa0402SLasse Collin * The fastest versions of xz_crc32() on modern CPUs without hardware
24fa0402SLasse Collin * accelerated CRC instruction are 3-5 times as fast as this version,
24fa0402SLasse Collin * but they are bigger and use more memory for the lookup table.
24fa0402SLasse Collin */
24fa0402SLasse Collin
24fa0402SLasse Collin#include "xz_private.h"
24fa0402SLasse Collin
24fa0402SLasse Collin/*
24fa0402SLasse Collin * STATIC_RW_DATA is used in the pre-boot environment on some architectures.
24fa0402SLasse Collin * See <linux/decompress/mm.h> for details.
24fa0402SLasse Collin */
24fa0402SLasse Collin#ifndef STATIC_RW_DATA
24fa0402SLasse Collin#	define STATIC_RW_DATA static
24fa0402SLasse Collin#endif
24fa0402SLasse Collin
24fa0402SLasse CollinSTATIC_RW_DATA uint32_t xz_crc32_table[256];
24fa0402SLasse Collin
24fa0402SLasse CollinXZ_EXTERN void xz_crc32_init(void)
24fa0402SLasse Collin{
*b7d6e724SLasse Collin	const uint32_t poly = 0xEDB88320;
24fa0402SLasse Collin
24fa0402SLasse Collin	uint32_t i;
24fa0402SLasse Collin	uint32_t j;
24fa0402SLasse Collin	uint32_t r;
24fa0402SLasse Collin
24fa0402SLasse Collin	for (i = 0; i < 256; ++i) {
24fa0402SLasse Collin		r = i;
24fa0402SLasse Collin		for (j = 0; j < 8; ++j)
24fa0402SLasse Collin			r = (r >> 1) ^ (poly & ~((r & 1) - 1));
24fa0402SLasse Collin
24fa0402SLasse Collin		xz_crc32_table[i] = r;
24fa0402SLasse Collin	}
24fa0402SLasse Collin
24fa0402SLasse Collin	return;
24fa0402SLasse Collin}
24fa0402SLasse Collin
24fa0402SLasse CollinXZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
24fa0402SLasse Collin{
24fa0402SLasse Collin	crc = ~crc;
24fa0402SLasse Collin
24fa0402SLasse Collin	while (size != 0) {
24fa0402SLasse Collin		crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
24fa0402SLasse Collin		--size;
24fa0402SLasse Collin	}
24fa0402SLasse Collin
24fa0402SLasse Collin	return ~crc;
24fa0402SLasse Collin}