/*

   * Aug 8, 2011 Bob Pearson with help from Joakim Tjernlund and George Spelvin
   * cleaned up code to current version of sparse and added the slicing-by-8
   * algorithm to the closely similar existing slicing-by-4 algorithm.
   *

   * 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/module.h>

  #include <linux/types.h>

  #include <linux/sched.h>

  #include "crc32defs.h"

  #if CRC_LE_BITS > 8

  # define tole(x) ((__force u32) cpu_to_le32(x))

  #else

  # define tole(x) (x)
  #endif

  #if CRC_BE_BITS > 8

  # define tobe(x) ((__force u32) cpu_to_be32(x))

  #else
  # define tobe(x) (x)

  #endif

  #include "crc32table.h"
  
  MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");

  MODULE_DESCRIPTION("Various CRC32 calculations");

  MODULE_LICENSE("GPL");

  #if CRC_LE_BITS > 8 || CRC_BE_BITS > 8

  /* implements slicing-by-4 or slicing-by-8 algorithm */

  static inline u32 __pure

  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 (t3[(q) & 255] ^ t2[(q >> 8) & 255] ^ \
  		   t1[(q >> 16) & 255] ^ t0[(q >> 24) & 255])
  #  define DO_CRC8 (t7[(q) & 255] ^ t6[(q >> 8) & 255] ^ \
  		   t5[(q >> 16) & 255] ^ t4[(q >> 24) & 255])

  # else

  #  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)

  #  define DO_CRC4 (t0[(q) & 255] ^ t1[(q >> 8) & 255] ^ \
  		   t2[(q >> 16) & 255] ^ t3[(q >> 24) & 255])
  #  define DO_CRC8 (t4[(q) & 255] ^ t5[(q >> 8) & 255] ^ \
  		   t6[(q >> 16) & 255] ^ t7[(q >> 24) & 255])

  # endif

  	const u32 *b;

  	size_t    rem_len;

  # ifdef CONFIG_X86
  	size_t i;
  # endif

  	const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];

  # if CRC_LE_BITS != 32

  	const u32 *t4 = tab[4], *t5 = tab[5], *t6 = tab[6], *t7 = tab[7];

  # endif

  	u32 q;

  
  	/* Align it */

  	if (unlikely((long)buf & 3 && len)) {

  		do {

  			DO_CRC(*buf++);
  		} while ((--len) && ((long)buf)&3);

  	}

  
  # if CRC_LE_BITS == 32

  	rem_len = len & 3;

  	len = len >> 2;

  # else
  	rem_len = len & 7;
  	len = len >> 3;
  # endif

  	b = (const u32 *)buf;

  # ifdef CONFIG_X86
  	--b;
  	for (i = 0; i < len; i++) {
  # else

  	for (--b; len; --len) {

  # endif

  		q = crc ^ *++b; /* use pre increment for speed */
  # if CRC_LE_BITS == 32
  		crc = DO_CRC4;
  # else
  		crc = DO_CRC8;
  		q = *++b;
  		crc ^= DO_CRC4;
  # endif

  	}
  	len = rem_len;
  	/* And the last few bytes */
  	if (len) {
  		u8 *p = (u8 *)(b + 1) - 1;

  # ifdef CONFIG_X86
  		for (i = 0; i < len; i++)
  			DO_CRC(*++p); /* use pre increment for speed */
  # else

  		do {
  			DO_CRC(*++p); /* use pre increment for speed */
  		} while (--len);

  # endif

  	}
  	return crc;

  #undef DO_CRC

  #undef DO_CRC4

  #undef DO_CRC8

  }
  #endif

  /**

   * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II
   *			CRC32/CRC32C
   * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for other
   *	 uses, or the previous crc32/crc32c value if computing incrementally.
   * @p: pointer to buffer over which CRC32/CRC32C is run

   * @len: length of buffer @p

   * @tab: little-endian Ethernet table
   * @polynomial: CRC32/CRC32c LE polynomial

   */

  static inline u32 __pure crc32_le_generic(u32 crc, unsigned char const *p,
  					  size_t len, const u32 (*tab)[256],
  					  u32 polynomial)

  {

  #if CRC_LE_BITS == 1

  	int i;
  	while (len--) {
  		crc ^= *p++;
  		for (i = 0; i < 8; i++)

  			crc = (crc >> 1) ^ ((crc & 1) ? polynomial : 0);

  	}

  # elif CRC_LE_BITS == 2

  	while (len--) {
  		crc ^= *p++;

  		crc = (crc >> 2) ^ tab[0][crc & 3];
  		crc = (crc >> 2) ^ tab[0][crc & 3];
  		crc = (crc >> 2) ^ tab[0][crc & 3];
  		crc = (crc >> 2) ^ tab[0][crc & 3];

  	}

  # elif CRC_LE_BITS == 4

  	while (len--) {
  		crc ^= *p++;

  		crc = (crc >> 4) ^ tab[0][crc & 15];
  		crc = (crc >> 4) ^ tab[0][crc & 15];

  	}

  # elif CRC_LE_BITS == 8

  	/* aka Sarwate algorithm */
  	while (len--) {
  		crc ^= *p++;

  		crc = (crc >> 8) ^ tab[0][crc & 255];

  	}
  # else

  	crc = (__force u32) __cpu_to_le32(crc);

  	crc = crc32_body(crc, p, len, tab);

  	crc = __le32_to_cpu((__force __le32)crc);

  #endif

  	return crc;

  }

  
  #if CRC_LE_BITS == 1
  u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
  {
  	return crc32_le_generic(crc, p, len, NULL, CRCPOLY_LE);
  }
  u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
  {
  	return crc32_le_generic(crc, p, len, NULL, CRC32C_POLY_LE);
  }
  #else
  u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
  {

  	return crc32_le_generic(crc, p, len,
  			(const u32 (*)[256])crc32table_le, CRCPOLY_LE);

  }
  u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
  {

  	return crc32_le_generic(crc, p, len,
  			(const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE);

  }
  #endif

  EXPORT_SYMBOL(crc32_le);
  EXPORT_SYMBOL(__crc32c_le);
  
  /*
   * This multiplies the polynomials x and y modulo the given modulus.
   * This follows the "little-endian" CRC convention that the lsbit
   * represents the highest power of x, and the msbit represents x^0.
   */
  static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
  {
  	u32 product = x & 1 ? y : 0;
  	int i;
  
  	for (i = 0; i < 31; i++) {
  		product = (product >> 1) ^ (product & 1 ? modulus : 0);
  		x >>= 1;
  		product ^= x & 1 ? y : 0;
  	}
  
  	return product;
  }
  
  /**
   * crc32_generic_shift - Append len 0 bytes to crc, in logarithmic time
   * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
   * @len: The number of bytes. @crc is multiplied by x^(8*@len)
   * @polynomial: The modulus used to reduce the result to 32 bits.
   *
   * It's possible to parallelize CRC computations by computing a CRC
   * over separate ranges of a buffer, then summing them.
   * This shifts the given CRC by 8*len bits (i.e. produces the same effect
   * as appending len bytes of zero to the data), in time proportional
   * to log(len).
   */
  static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
  						   u32 polynomial)
  {
  	u32 power = polynomial;	/* CRC of x^32 */
  	int i;
  
  	/* Shift up to 32 bits in the simple linear way */
  	for (i = 0; i < 8 * (int)(len & 3); i++)
  		crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
  
  	len >>= 2;
  	if (!len)
  		return crc;
  
  	for (;;) {
  		/* "power" is x^(2^i), modulo the polynomial */
  		if (len & 1)
  			crc = gf2_multiply(crc, power, polynomial);
  
  		len >>= 1;
  		if (!len)
  			break;
  
  		/* Square power, advancing to x^(2^(i+1)) */
  		power = gf2_multiply(power, power, polynomial);
  	}
  
  	return crc;
  }
  
  u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)

  {

  	return crc32_generic_shift(crc, len, CRCPOLY_LE);

  }

  u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)

  {

  	return crc32_generic_shift(crc, len, CRC32C_POLY_LE);

  }

  EXPORT_SYMBOL(crc32_le_shift);
  EXPORT_SYMBOL(__crc32c_le_shift);

  /**

   * crc32_be_generic() - 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 CRC32 is run

   * @len: length of buffer @p

   * @tab: big-endian Ethernet table
   * @polynomial: CRC32 BE polynomial

   */

  static inline u32 __pure crc32_be_generic(u32 crc, unsigned char const *p,
  					  size_t len, const u32 (*tab)[256],
  					  u32 polynomial)

  {

  #if CRC_BE_BITS == 1

  	int i;
  	while (len--) {
  		crc ^= *p++ << 24;
  		for (i = 0; i < 8; i++)
  			crc =

  			    (crc << 1) ^ ((crc & 0x80000000) ? polynomial :

  					  0);
  	}

  # elif CRC_BE_BITS == 2

  	while (len--) {
  		crc ^= *p++ << 24;

  		crc = (crc << 2) ^ tab[0][crc >> 30];
  		crc = (crc << 2) ^ tab[0][crc >> 30];
  		crc = (crc << 2) ^ tab[0][crc >> 30];
  		crc = (crc << 2) ^ tab[0][crc >> 30];

  	}

  # elif CRC_BE_BITS == 4

  	while (len--) {
  		crc ^= *p++ << 24;

  		crc = (crc << 4) ^ tab[0][crc >> 28];
  		crc = (crc << 4) ^ tab[0][crc >> 28];

  	}

  # elif CRC_BE_BITS == 8

  	while (len--) {
  		crc ^= *p++ << 24;

  		crc = (crc << 8) ^ tab[0][crc >> 24];

  	}
  # else

  	crc = (__force u32) __cpu_to_be32(crc);

  	crc = crc32_body(crc, p, len, tab);

  	crc = __be32_to_cpu((__force __be32)crc);

  # endif

  	return crc;

  }

  
  #if CRC_LE_BITS == 1
  u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
  {
  	return crc32_be_generic(crc, p, len, NULL, CRCPOLY_BE);
  }
  #else
  u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
  {

  	return crc32_be_generic(crc, p, len,
  			(const u32 (*)[256])crc32table_be, CRCPOLY_BE);

  }
  #endif

  EXPORT_SYMBOL(crc32_be);