#ifndef _LINUX_JHASH_H
  #define _LINUX_JHASH_H
  
  /* jhash.h: Jenkins hash support.
   *
   * Copyright (C) 2006. Bob Jenkins (bob_jenkins@burtleburtle.net)
   *
   * http://burtleburtle.net/bob/hash/
   *
   * These are the credits from Bob's sources:
   *
   * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
   *
   * These are functions for producing 32-bit hashes for hash table lookup.
   * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
   * are externally useful functions.  Routines to test the hash are included
   * if SELF_TEST is defined.  You can use this free for any purpose.  It's in
   * the public domain.  It has no warranty.
   *
   * Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu)
   *
   * I've modified Bob's hash to be useful in the Linux kernel, and
   * any bugs present are my fault.
   * Jozsef
   */
  #include <linux/bitops.h>
  #include <linux/unaligned/packed_struct.h>
  
  /* Best hash sizes are of power of two */
  #define jhash_size(n)   ((u32)1<<(n))
  /* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */
  #define jhash_mask(n)   (jhash_size(n)-1)
  
  /* __jhash_mix -- mix 3 32-bit values reversibly. */
  #define __jhash_mix(a, b, c)			\
  {						\
  	a -= c;  a ^= rol32(c, 4);  c += b;	\
  	b -= a;  b ^= rol32(a, 6);  a += c;	\
  	c -= b;  c ^= rol32(b, 8);  b += a;	\
  	a -= c;  a ^= rol32(c, 16); c += b;	\
  	b -= a;  b ^= rol32(a, 19); a += c;	\
  	c -= b;  c ^= rol32(b, 4);  b += a;	\
  }
  
  /* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
  #define __jhash_final(a, b, c)			\
  {						\
  	c ^= b; c -= rol32(b, 14);		\
  	a ^= c; a -= rol32(c, 11);		\
  	b ^= a; b -= rol32(a, 25);		\
  	c ^= b; c -= rol32(b, 16);		\
  	a ^= c; a -= rol32(c, 4);		\
  	b ^= a; b -= rol32(a, 14);		\
  	c ^= b; c -= rol32(b, 24);		\
  }
  
  /* An arbitrary initial parameter */
  #define JHASH_INITVAL		0xdeadbeef
  
  /* jhash - hash an arbitrary key
   * @k: sequence of bytes as key
   * @length: the length of the key
   * @initval: the previous hash, or an arbitray value
   *
   * The generic version, hashes an arbitrary sequence of bytes.
   * No alignment or length assumptions are made about the input key.
   *
   * Returns the hash value of the key. The result depends on endianness.
   */
  static inline u32 jhash(const void *key, u32 length, u32 initval)
  {
  	u32 a, b, c;
  	const u8 *k = key;
  
  	/* Set up the internal state */
  	a = b = c = JHASH_INITVAL + length + initval;
  
  	/* All but the last block: affect some 32 bits of (a,b,c) */
  	while (length > 12) {
  		a += __get_unaligned_cpu32(k);
  		b += __get_unaligned_cpu32(k + 4);
  		c += __get_unaligned_cpu32(k + 8);
  		__jhash_mix(a, b, c);
  		length -= 12;
  		k += 12;
  	}
  	/* Last block: affect all 32 bits of (c) */
  	/* All the case statements fall through */
  	switch (length) {
  	case 12: c += (u32)k[11]<<24;
  	case 11: c += (u32)k[10]<<16;
  	case 10: c += (u32)k[9]<<8;
  	case 9:  c += k[8];
  	case 8:  b += (u32)k[7]<<24;
  	case 7:  b += (u32)k[6]<<16;
  	case 6:  b += (u32)k[5]<<8;
  	case 5:  b += k[4];
  	case 4:  a += (u32)k[3]<<24;
  	case 3:  a += (u32)k[2]<<16;
  	case 2:  a += (u32)k[1]<<8;
  	case 1:  a += k[0];
  		 __jhash_final(a, b, c);
  	case 0: /* Nothing left to add */
  		break;
  	}
  
  	return c;
  }
  
  /* jhash2 - hash an array of u32's
   * @k: the key which must be an array of u32's
   * @length: the number of u32's in the key
   * @initval: the previous hash, or an arbitray value
   *
   * Returns the hash value of the key.
   */
  static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
  {
  	u32 a, b, c;
  
  	/* Set up the internal state */
  	a = b = c = JHASH_INITVAL + (length<<2) + initval;
  
  	/* Handle most of the key */
  	while (length > 3) {
  		a += k[0];
  		b += k[1];
  		c += k[2];
  		__jhash_mix(a, b, c);
  		length -= 3;
  		k += 3;
  	}
  
  	/* Handle the last 3 u32's: all the case statements fall through */
  	switch (length) {
  	case 3: c += k[2];
  	case 2: b += k[1];
  	case 1: a += k[0];
  		__jhash_final(a, b, c);
  	case 0:	/* Nothing left to add */
  		break;
  	}
  
  	return c;
  }
  
  
  /* jhash_3words - hash exactly 3, 2 or 1 word(s) */
  static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
  {
  	a += JHASH_INITVAL;
  	b += JHASH_INITVAL;
  	c += initval;
  
  	__jhash_final(a, b, c);
  
  	return c;
  }
  
  static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
  {
  	return jhash_3words(a, b, 0, initval);
  }
  
  static inline u32 jhash_1word(u32 a, u32 initval)
  {
  	return jhash_3words(a, 0, 0, initval);
  }
  
  #endif /* _LINUX_JHASH_H */