/* * 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. */ #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 u32crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256]){# ifdef __LITTLE_ENDIAN#  define DO_CRC(x) crc = tab[0][(crc ^ (x)) & 255] ^ (crc >> 8)#  define DO_CRC4 crc = tab[3][(crc) & 255] ^ \		tab[2][(crc >> 8) & 255] ^ \		tab[1][(crc >> 16) & 255] ^ \		tab[0][(crc >> 24) & 255]# else#  define DO_CRC(x) crc = tab[0][((crc >> 24) ^ (x)) & 255] ^ (crc << 8)#  define DO_CRC4 crc = tab[0][(crc) & 255] ^ \		tab[1][(crc >> 8) & 255] ^ \		tab[2][(crc >> 16) & 255] ^ \		tab[3][(crc >> 24) & 255]# endif	const u32 *b;	size_t    rem_len; 	/* 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); /* * A brief CRC tutorial. * * A CRC is a long-division remainder.  You add the CRC to the message, * and the whole thing (message+CRC) is a multiple of the given * CRC polynomial.  To check the CRC, you can either check that the * CRC matches the recomputed value, *or* you can check that the * remainder computed on the message+CRC is 0.  This latter approach * is used by a lot of hardware implementations, and is why so many * protocols put the end-of-frame flag after the CRC. * * It's actually the same long division you learned in school, except that * - We're working in binary, so the digits are only 0 and 1, and * - When dividing polynomials, there are no carries.  Rather than add and *   subtract, we just xor.  Thus, we tend to get a bit sloppy about *   the difference between adding and subtracting. * * A 32-bit CRC polynomial is actually 33 bits long.  But since it's * 33 bits long, bit 32 is always going to be set, so usually the CRC * is written in hex with the most significant bit omitted.  (If you're * familiar with the IEEE 754 floating-point format, it's the same idea.) * * Note that a CRC is computed over a string of *bits*, so you have * to decide on the endianness of the bits within each byte.  To get * the best error-detecting properties, this should correspond to the * order they're actually sent.  For example, standard RS-232 serial is * little-endian; the most significant bit (sometimes used for parity) * is sent last.  And when appending a CRC word to a message, you should * do it in the right order, matching the endianness. * * Just like with ordinary division, the remainder is always smaller than * the divisor (the CRC polynomial) you're dividing by.  Each step of the * division, you take one more digit (bit) of the dividend and append it * to the current remainder.  Then you figure out the appropriate multiple * of the divisor to subtract to being the remainder back into range. * In binary, it's easy - it has to be either 0 or 1, and to make the * XOR cancel, it's just a copy of bit 32 of the remainder. * * When computing a CRC, we don't care about the quotient, so we can * throw the quotient bit away, but subtract the appropriate multiple of * the polynomial from the remainder and we're back to where we started, * ready to process the next bit. * * A big-endian CRC written this way would be coded like: * for (i = 0; i < input_bits; i++) { * 	multiple = remainder & 0x80000000 ? CRCPOLY : 0; * 	remainder = (remainder << 1 | next_input_bit()) ^ multiple; * } * Notice how, to get at bit 32 of the shifted remainder, we look * at bit 31 of the remainder *before* shifting it. * * But also notice how the next_input_bit() bits we're shifting into * the remainder don't actually affect any decision-making until * 32 bits later.  Thus, the first 32 cycles of this are pretty boring. * Also, to add the CRC to a message, we need a 32-bit-long hole for it at * the end, so we have to add 32 extra cycles shifting in zeros at the * end of every message, * * So the standard trick is to rearrage merging in the next_input_bit() * until the moment it's needed.  Then the first 32 cycles can be precomputed, * and merging in the final 32 zero bits to make room for the CRC can be * skipped entirely. * This changes the code to: * for (i = 0; i < input_bits; i++) { *      remainder ^= next_input_bit() << 31; * 	multiple = (remainder & 0x80000000) ? CRCPOLY : 0; * 	remainder = (remainder << 1) ^ multiple; * } * With this optimization, the little-endian code is simpler: * for (i = 0; i < input_bits; i++) { *      remainder ^= next_input_bit(); * 	multiple = (remainder & 1) ? CRCPOLY : 0; * 	remainder = (remainder >> 1) ^ multiple; * } * * Note that the other details of endianness have been hidden in CRCPOLY * (which must be bit-reversed) and next_input_bit(). * * However, as long as next_input_bit is returning the bits in a sensible * order, we can actually do the merging 8 or more bits at a time rather * than one bit at a time: * for (i = 0; i < input_bytes; i++) { * 	remainder ^= next_input_byte() << 24; * 	for (j = 0; j < 8; j++) { * 		multiple = (remainder & 0x80000000) ? CRCPOLY : 0; * 		remainder = (remainder << 1) ^ multiple; * 	} * } * Or in little-endian: * for (i = 0; i < input_bytes; i++) { * 	remainder ^= next_input_byte(); * 	for (j = 0; j < 8; j++) { * 		multiple = (remainder & 1) ? CRCPOLY : 0; * 		remainder = (remainder << 1) ^ multiple; * 	} * } * If the input is a multiple of 32 bits, you can even XOR in a 32-bit * word at a time and increase the inner loop count to 32. * * You can also mix and match the two loop styles, for example doing the * bulk of a message byte-at-a-time and adding bit-at-a-time processing * for any fractional bytes at the end. * * The only remaining optimization is to the byte-at-a-time table method. * Here, rather than just shifting one bit of the remainder to decide * in the correct multiple to subtract, we can shift a byte at a time. * This produces a 40-bit (rather than a 33-bit) intermediate remainder, * but again the multiple of the polynomial to subtract depends only on * the high bits, the high 8 bits in this case.   * * The multiple we need in that case is the low 32 bits of a 40-bit * value whose high 8 bits are given, and which is a multiple of the * generator polynomial.  This is simply the CRC-32 of the given * one-byte message. * * Two more details: normally, appending zero bits to a message which * is already a multiple of a polynomial produces a larger multiple of that * polynomial.  To enable a CRC to detect this condition, it's common to * invert the CRC before appending it.  This makes the remainder of the * message+crc come out not as zero, but some fixed non-zero value. * * The same problem applies to zero bits prepended to the message, and * a similar solution is used.  Instead of starting with a remainder of * 0, an initial remainder of all ones is used.  As long as you start * the same way on decoding, it doesn't make a difference. */ #ifdef UNITTEST #include <stdlib.h>#include <stdio.h> #if 0				/*Not used at present */static voidbuf_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 */