/* crc.c - crc function  */
/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2008  Free Software Foundation, Inc.
 *
 *  GRUB 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 3 of the License, or
 *  (at your option) any later version.
 *
 *  GRUB 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 License
 *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <grub/types.h>
#include <grub/lib/crc.h>

static grub_uint32_t crc32c_table[256];

/* Helper for init_crc32c_table.  */
static grub_uint32_t
reflect(grub_uint32_t ref, int len)
{
	grub_uint32_t result = 0;
	int i;

	for (i = 1; i <= len; i++)
	{
		if (ref & 1)
			result |= 1 << (len - i);
		ref >>= 1;
	}

	return result;
}

static void
init_crc32c_table(void)
{
	grub_uint32_t polynomial = 0x1edc6f41;
	int i, j;

	for (i = 0; i < 256; i++)
	{
		crc32c_table[i] = reflect(i, 8) << 24;
		for (j = 0; j < 8; j++)
			crc32c_table[i] = (crc32c_table[i] << 1) ^
			(crc32c_table[i] & (1 << 31) ? polynomial : 0);
		crc32c_table[i] = reflect(crc32c_table[i], 32);
	}
}

grub_uint32_t
grub_getcrc32c(grub_uint32_t crc, const void* buf, int size)
{
	int i;
	const grub_uint8_t* data = buf;

	if (!crc32c_table[1])
		init_crc32c_table();

	crc ^= 0xffffffff;

	for (i = 0; i < size; i++)
	{
		crc = (crc >> 8) ^ crc32c_table[(crc & 0xFF) ^ *data];
		data++;
	}

	return crc ^ 0xffffffff;
}
