src/boot/crc32.c

/*
 * Copyright 2014 Google Inc.
 *
 * This file is derived from crc32.c from the zlib-1.1.3 distribution
 * by Jean-loup Gailly and Mark Adler.
 *
 * crc32.c -- compute the CRC-32 of a data stream
 * Copyright (C) 1995-1998 Mark Adler
 *
 * See file CREDITS for list of people who contributed to this project.
 *
 * This program 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 2 of the License, or (at your option)
 * any later version.
 *
 * This program 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 this program; if not, write to the Free Software Foundation, Inc., 59
 * Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include <libpayload.h>
#include <endian.h>

#include "crc32.h"


static int crc_table_empty = 1;
static uint32_t crc_table[256];
static void make_crc_table (void);

/*
  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.

  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), 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+...+1), 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.
*/
/* terms of polynomial defining this crc (except x^32): */
static const uint8_t p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};

static void make_crc_table(void)
{
	uint32_t c;
	int n, k;
	uint32_t poly;		/* polynomial exclusive-or pattern */

	/* make exclusive-or pattern from polynomial (0xedb88320L) */
	poly = 0L;
	for (n = 0; n < sizeof(p)/sizeof(uint8_t); n++)
		poly |= 1L << (31 - p[n]);

	for (n = 0; n < 256; n++) {
		c = (uint32_t)n;
		for (k = 0; k < 8; k++)
			c = c & 1 ? poly ^ (c >> 1) : c >> 1;
		crc_table[n] = htole32(c);
	}
	crc_table_empty = 0;
}

/* ========================================================================= */
#  define DO_CRC(x) crc = tab[(crc ^ (x)) & 255] ^ (crc >> 8)

/* ========================================================================= */

/* No ones complement version. JFFS2 (and other things ?)
 * don't use ones compliment in their CRC calculations.
 */
static uint32_t crc32_no_comp(uint32_t crc, const void *p, unsigned len)
{
	const uint8_t *buf = p;
	const uint32_t *tab = crc_table;
	const uint32_t *b =(const uint32_t *)buf;
	size_t rem_len;
	if (crc_table_empty)
		make_crc_table();
	crc = htole32(crc);
	/* Align it */
	if (((long)b) & 3 && len) {
		uint8_t *p = (uint8_t *)b;
		do {
			DO_CRC(*p++);
		} while ((--len) && ((long)p)&3);
		b = (uint32_t *)p;
	}

	rem_len = len & 3;
	len = len >> 2;
	for (--b; len; --len) {
		/* load data 32 bits wide, xor data 32 bits wide. */
		crc ^= *++b; /* use pre increment for speed */
		DO_CRC(0);
		DO_CRC(0);
		DO_CRC(0);
		DO_CRC(0);
	}
	len = rem_len;
	/* And the last few bytes */
	if (len) {
		uint8_t *p = (uint8_t *)(b + 1) - 1;
		do {
			DO_CRC(*++p); /* use pre increment for speed */
		} while (--len);
	}

	return le32toh(crc);
}
#undef DO_CRC

uint32_t crc32 (uint32_t crc, const void *p, unsigned len)
{
	return crc32_no_comp(crc ^ 0xffffffffL, p, len) ^ 0xffffffffL;
}