path: root/lib/crc32.c

/*
 * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
 * Nicer crc32 functions/docs submitted by linux@horizon.com.  Thanks!
 * Code was from the public domain, copyright abandoned.  Code was
 * subsequently included in the kernel, thus was re-licensed under the
 * GNU GPL v2.
 *
 * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
 * Same crc32 function was used in 5 other places in the kernel.
 * I made one version, and deleted the others.
 * There are various incantations of crc32().  Some use a seed of 0 or ~0.
 * Some xor at the end with ~0.  The generic crc32() function takes
 * seed as an argument, and doesn't xor at the end.  Then individual
 * users can do whatever they need.
 *   drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
 *   fs/jffs2 uses seed 0, doesn't xor with ~0.
 *   fs/partitions/efi.c uses seed ~0, xor's with ~0.
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2.  See the file COPYING for more details.
 */

/* see: Documentation/crc32.txt for a description of algorithms */

#include <linux/crc32.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/atomic.h>
#include "crc32defs.h"
#if CRC_LE_BITS == 8
# define tole(x) __constant_cpu_to_le32(x)
#else
# define tole(x) (x)
#endif

#if CRC_BE_BITS == 8
# define tobe(x) __constant_cpu_to_be32(x)
#else
# define tobe(x) (x)
#endif
#include "crc32table.h"

MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
MODULE_DESCRIPTION("Ethernet CRC32 calculations");
MODULE_LICENSE("GPL");

#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8

static inline u32
crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
{
# ifdef __LITTLE_ENDIAN
#  define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
#  define DO_CRC4 crc = t3[(crc) & 255] ^ \
		t2[(crc >> 8) & 255] ^ \
		t1[(crc >> 16) & 255] ^ \
		t0[(crc >> 24) & 255]
# else
#  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
#  define DO_CRC4 crc = t0[(crc) & 255] ^ \
		t1[(crc >> 8) & 255] ^  \
		t2[(crc >> 16) & 255] ^	\
		t3[(crc >> 24) & 255]
# endif
	const u32 *b;
	size_t    rem_len;
	const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];

	/* Align it */
	if (unlikely((long)buf & 3 && len)) {
		do {
			DO_CRC(*buf++);
		} while ((--len) && ((long)buf)&3);
	}
	rem_len = len & 3;
	/* load data 32 bits wide, xor data 32 bits wide. */
	len = len >> 2;
	b = (const u32 *)buf;
	for (--b; len; --len) {
		crc ^= *++b; /* use pre increment for speed */
		DO_CRC4;
	}
	len = rem_len;
	/* And the last few bytes */
	if (len) {
		u8 *p = (u8 *)(b + 1) - 1;
		do {
			DO_CRC(*++p); /* use pre increment for speed */
		} while (--len);
	}
	return crc;
#undef DO_CRC
#undef DO_CRC4
}
#endif
/**
 * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
 * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for
 *	other uses, or the previous crc32 value if computing incrementally.
 * @p: pointer to buffer over which CRC is run
 * @len: length of buffer @p
 */
u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);

#if CRC_LE_BITS == 1
/*
 * In fact, the table-based code will work in this case, but it can be
 * simplified by inlining the table in ?: form.
 */

u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
{
	int i;
	while (len--) {
		crc ^= *p++;
		for (i = 0; i < 8; i++)
			crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
	}
	return crc;
}
#else				/* Table-based approach */

u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
{
# if CRC_LE_BITS == 8
	const u32      (*tab)[] = crc32table_le;

	crc = __cpu_to_le32(crc);
	crc = crc32_body(crc, p, len, tab);
	return __le32_to_cpu(crc);
# elif CRC_LE_BITS == 4
	while (len--) {
		crc ^= *p++;
		crc = (crc >> 4) ^ crc32table_le[crc & 15];
		crc = (crc >> 4) ^ crc32table_le[crc & 15];
	}
	return crc;
# elif CRC_LE_BITS == 2
	while (len--) {
		crc ^= *p++;
		crc = (crc >> 2) ^ crc32table_le[crc & 3];
		crc = (crc >> 2) ^ crc32table_le[crc & 3];
		crc = (crc >> 2) ^ crc32table_le[crc & 3];
		crc = (crc >> 2) ^ crc32table_le[crc & 3];
	}
	return crc;
# endif
}
#endif

/**
 * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
 * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for
 *	other uses, or the previous crc32 value if computing incrementally.
 * @p: pointer to buffer over which CRC is run
 * @len: length of buffer @p
 */
u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);

#if CRC_BE_BITS == 1
/*
 * In fact, the table-based code will work in this case, but it can be
 * simplified by inlining the table in ?: form.
 */

u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
{
	int i;
	while (len--) {
		crc ^= *p++ << 24;
		for (i = 0; i < 8; i++)
			crc =
			    (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
					  0);
	}
	return crc;
}

#else				/* Table-based approach */
u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
{
# if CRC_BE_BITS == 8
	const u32      (*tab)[] = crc32table_be;

	crc = __cpu_to_be32(crc);
	crc = crc32_body(crc, p, len, tab);
	return __be32_to_cpu(crc);
# elif CRC_BE_BITS == 4
	while (len--) {
		crc ^= *p++ << 24;
		crc = (crc << 4) ^ crc32table_be[crc >> 28];
		crc = (crc << 4) ^ crc32table_be[crc >> 28];
	}
	return crc;
# elif CRC_BE_BITS == 2
	while (len--) {
		crc ^= *p++ << 24;
		crc = (crc << 2) ^ crc32table_be[crc >> 30];
		crc = (crc << 2) ^ crc32table_be[crc >> 30];
		crc = (crc << 2) ^ crc32table_be[crc >> 30];
		crc = (crc << 2) ^ crc32table_be[crc >> 30];
	}
	return crc;
# endif
}
#endif

EXPORT_SYMBOL(crc32_le);
EXPORT_SYMBOL(crc32_be);

#ifdef UNITTEST

#include <stdlib.h>
#include <stdio.h>

#if 0				/*Not used at present */
static void
buf_dump(char const *prefix, unsigned char const *buf, size_t len)
{
	fputs(prefix, stdout);
	while (len--)
		printf(" %02x", *buf++);
	putchar('\n');

}
#endif

static void bytereverse(unsigned char *buf, size_t len)
{
	while (len--) {
		unsigned char x = bitrev8(*buf);
		*buf++ = x;
	}
}

static void random_garbage(unsigned char *buf, size_t len)
{
	while (len--)
		*buf++ = (unsigned char) random();
}

#if 0				/* Not used at present */
static void store_le(u32 x, unsigned char *buf)
{
	buf[0] = (unsigned char) x;
	buf[1] = (unsigned char) (x >> 8);
	buf[2] = (unsigned char) (x >> 16);
	buf[3] = (unsigned char) (x >> 24);
}
#endif

static void store_be(u32 x, unsigned char *buf)
{
	buf[0] = (unsigned char) (x >> 24);
	buf[1] = (unsigned char) (x >> 16);
	buf[2] = (unsigned char) (x >> 8);
	buf[3] = (unsigned char) x;
}

/*
 * This checks that CRC(buf + CRC(buf)) = 0, and that
 * CRC commutes with bit-reversal.  This has the side effect
 * of bytewise bit-reversing the input buffer, and returns
 * the CRC of the reversed buffer.
 */
static u32 test_step(u32 init, unsigned char *buf, size_t len)
{
	u32 crc1, crc2;
	size_t i;

	crc1 = crc32_be(init, buf, len);
	store_be(crc1, buf + len);
	crc2 = crc32_be(init, buf, len + 4);
	if (crc2)
		printf("\nCRC cancellation fail: 0x%08x should be 0\n",
		       crc2);

	for (i = 0; i <= len + 4; i++) {
		crc2 = crc32_be(init, buf, i);
		crc2 = crc32_be(crc2, buf + i, len + 4 - i);
		if (crc2)
			printf("\nCRC split fail: 0x%08x\n", crc2);
	}

	/* Now swap it around for the other test */

	bytereverse(buf, len + 4);
	init = bitrev32(init);
	crc2 = bitrev32(crc1);
	if (crc1 != bitrev32(crc2))
		printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
		       crc1, crc2, bitrev32(crc2));
	crc1 = crc32_le(init, buf, len);
	if (crc1 != crc2)
		printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
		       crc2);
	crc2 = crc32_le(init, buf, len + 4);
	if (crc2)
		printf("\nCRC cancellation fail: 0x%08x should be 0\n",
		       crc2);

	for (i = 0; i <= len + 4; i++) {
		crc2 = crc32_le(init, buf, i);
		crc2 = crc32_le(crc2, buf + i, len + 4 - i);
		if (crc2)
			printf("\nCRC split fail: 0x%08x\n", crc2);
	}

	return crc1;
}

#define SIZE 64
#define INIT1 0
#define INIT2 0

int main(void)
{
	unsigned char buf1[SIZE + 4];
	unsigned char buf2[SIZE + 4];
	unsigned char buf3[SIZE + 4];
	int i, j;
	u32 crc1, crc2, crc3;

	for (i = 0; i <= SIZE; i++) {
		printf("\rTesting length %d...", i);
		fflush(stdout);
		random_garbage(buf1, i);
		random_garbage(buf2, i);
		for (j = 0; j < i; j++)
			buf3[j] = buf1[j] ^ buf2[j];

		crc1 = test_step(INIT1, buf1, i);
		crc2 = test_step(INIT2, buf2, i);
		/* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
		crc3 = test_step(INIT1 ^ INIT2, buf3, i);
		if (crc3 != (crc1 ^ crc2))
			printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
			       crc3, crc1, crc2);
	}
	printf("\nAll test complete.  No failures expected.\n");
	return 0;
}

#endif				/* UNITTEST */