#include <linux/ceph/types.h>

  #include <linux/module.h>

  
  /*
   * Robert Jenkin's hash function.

   * https://burtleburtle.net/bob/hash/evahash.html

   * This is in the public domain.
   */
  #define mix(a, b, c)						\
  	do {							\
  		a = a - b;  a = a - c;  a = a ^ (c >> 13);	\
  		b = b - c;  b = b - a;  b = b ^ (a << 8);	\
  		c = c - a;  c = c - b;  c = c ^ (b >> 13);	\
  		a = a - b;  a = a - c;  a = a ^ (c >> 12);	\
  		b = b - c;  b = b - a;  b = b ^ (a << 16);	\
  		c = c - a;  c = c - b;  c = c ^ (b >> 5);	\
  		a = a - b;  a = a - c;  a = a ^ (c >> 3);	\
  		b = b - c;  b = b - a;  b = b ^ (a << 10);	\
  		c = c - a;  c = c - b;  c = c ^ (b >> 15);	\
  	} while (0)

  unsigned int ceph_str_hash_rjenkins(const char *str, unsigned int length)

  {
  	const unsigned char *k = (const unsigned char *)str;
  	__u32 a, b, c;  /* the internal state */
  	__u32 len;      /* how many key bytes still need mixing */
  
  	/* Set up the internal state */
  	len = length;
  	a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
  	b = a;
  	c = 0;               /* variable initialization of internal state */
  
  	/* handle most of the key */
  	while (len >= 12) {
  		a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
  			 ((__u32)k[3] << 24));
  		b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
  			 ((__u32)k[7] << 24));
  		c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
  			 ((__u32)k[11] << 24));
  		mix(a, b, c);
  		k = k + 12;
  		len = len - 12;
  	}
  
  	/* handle the last 11 bytes */
  	c = c + length;

  	switch (len) {

  	case 11:
  		c = c + ((__u32)k[10] << 24);

  		fallthrough;

  	case 10:
  		c = c + ((__u32)k[9] << 16);

  		fallthrough;

  	case 9:
  		c = c + ((__u32)k[8] << 8);
  		/* the first byte of c is reserved for the length */

  		fallthrough;

  	case 8:
  		b = b + ((__u32)k[7] << 24);

  		fallthrough;

  	case 7:
  		b = b + ((__u32)k[6] << 16);

  		fallthrough;

  	case 6:
  		b = b + ((__u32)k[5] << 8);

  		fallthrough;

  	case 5:
  		b = b + k[4];

  		fallthrough;

  	case 4:
  		a = a + ((__u32)k[3] << 24);

  		fallthrough;

  	case 3:
  		a = a + ((__u32)k[2] << 16);

  		fallthrough;

  	case 2:
  		a = a + ((__u32)k[1] << 8);

  		fallthrough;

  	case 1:
  		a = a + k[0];
  		/* case 0: nothing left to add */
  	}
  	mix(a, b, c);
  
  	return c;
  }
  
  /*
   * linux dcache hash
   */

  unsigned int ceph_str_hash_linux(const char *str, unsigned int length)

  {

  	unsigned long hash = 0;

  	unsigned char c;

  	while (length--) {

  		c = *str++;
  		hash = (hash + (c << 4) + (c >> 4)) * 11;
  	}

  	return hash;

  }

  unsigned int ceph_str_hash(int type, const char *s, unsigned int len)

  {
  	switch (type) {
  	case CEPH_STR_HASH_LINUX:
  		return ceph_str_hash_linux(s, len);
  	case CEPH_STR_HASH_RJENKINS:
  		return ceph_str_hash_rjenkins(s, len);
  	default:
  		return -1;
  	}
  }

  EXPORT_SYMBOL(ceph_str_hash);

  const char *ceph_str_hash_name(int type)

  {
  	switch (type) {
  	case CEPH_STR_HASH_LINUX:
  		return "linux";
  	case CEPH_STR_HASH_RJENKINS:
  		return "rjenkins";
  	default:
  		return "unknown";
  	}
  }

  EXPORT_SYMBOL(ceph_str_hash_name);