/*
   * 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 u32

  crc32_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 void
  buf_dump(char const *prefix, unsigned char const *buf, size_t len)
  {
  	fputs(prefix, stdout);
  	while (len--)
  		printf(" %02x", *buf++);
  	putchar('
  ');
  
  }
  #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("
  CRC cancellation fail: 0x%08x should be 0
  ",
  		       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("
  CRC split fail: 0x%08x
  ", crc2);
  	}
  
  	/* Now swap it around for the other test */
  
  	bytereverse(buf, len + 4);

  	init = bitrev32(init);
  	crc2 = bitrev32(crc1);
  	if (crc1 != bitrev32(crc2))

  		printf("
  Bit reversal fail: 0x%08x -> 0x%08x -> 0x%08x
  ",

  		       crc1, crc2, bitrev32(crc2));

  	crc1 = crc32_le(init, buf, len);
  	if (crc1 != crc2)
  		printf("
  CRC endianness fail: 0x%08x != 0x%08x
  ", crc1,
  		       crc2);
  	crc2 = crc32_le(init, buf, len + 4);
  	if (crc2)
  		printf("
  CRC cancellation fail: 0x%08x should be 0
  ",
  		       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("
  CRC split fail: 0x%08x
  ", 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
  ",
  			       crc3, crc1, crc2);
  	}
  	printf("
  All test complete.  No failures expected.
  ");
  	return 0;
  }
  
  #endif				/* UNITTEST */