polardbxengine/storage/innobase/include/ut0rnd.ic

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/** @file include/ut0rnd.ic
 Random numbers and hashing

 Created 5/30/1994 Heikki Tuuri
 *******************************************************************/

#define UT_HASH_RANDOM_MASK 1463735687
#define UT_HASH_RANDOM_MASK2 1653893711

#define UT_RND1 151117737
#define UT_RND2 119785373
#define UT_RND3 85689495
#define UT_RND4 76595339
#define UT_SUM_RND2 98781234
#define UT_SUM_RND3 126792457
#define UT_SUM_RND4 63498502
#define UT_XOR_RND1 187678878
#define UT_XOR_RND2 143537923

#include <my_thread_local.h>

/** Seed value of ut_rnd_gen_ulint() */
extern thread_local ulint ut_rnd_ulint_counter;

/** The following function generates a series of 'random' ulint integers.
 This function is now based on thread local variables.
 @return the next 'random' number */
UNIV_INLINE
ulint ut_rnd_gen_next_ulint(
    ulint rnd) /*!< in: the previous random number value */
{
  ulint n_bits;

  n_bits = 8 * sizeof(ulint);

  rnd = UT_RND2 * rnd + UT_SUM_RND3;
  rnd = UT_XOR_RND1 ^ rnd;
  rnd = (rnd << 20) + (rnd >> (n_bits - 20));
  rnd = UT_RND3 * rnd + UT_SUM_RND4;
  rnd = UT_XOR_RND2 ^ rnd;
  rnd = (rnd << 20) + (rnd >> (n_bits - 20));
  rnd = UT_RND1 * rnd + UT_SUM_RND2;

  return (rnd);
}

/** The following function generates 'random' ulint integers which
enumerate the value space of ulint integers in a pseudo random
fashion. Note that the same integer is repeated always after
2 to power 32 calls to the generator (if ulint is 32-bit).
@return pseudo random number */
ulint ut_rnd_gen_ulint() {
  ulint rnd = ut_rnd_ulint_counter;
  if (rnd == 0) {
    rnd = 65654363;
  }

  rnd = UT_RND1 * rnd + UT_RND2;

  ut_rnd_ulint_counter = rnd;

  return (ut_rnd_gen_next_ulint(rnd));
}

/** Generates a random integer from a given interval.
 This function is now based on thread local variables.
 @return the 'random' number */
UNIV_INLINE
ulint ut_rnd_interval(
    ulint low,  /*!< in: low limit; can generate also this value */
    ulint high) /*!< in: high limit; can generate also this value */
{
  ulint rnd;

  ut_ad(high >= low);

  if (low == high) {
    return (low);
  }

  rnd = ut_rnd_gen_ulint();

  return (low + (rnd % (high - low)));
}

/** The following function generates a hash value for a ulint integer
 to a hash table of size table_size, which should be a prime
 or some random number for the hash table to work reliably.
 @return hash value */
UNIV_INLINE
ulint ut_hash_ulint(ulint key,        /*!< in: value to be hashed */
                    ulint table_size) /*!< in: hash table size */
{
  ut_ad(table_size);
  key = key ^ UT_HASH_RANDOM_MASK2;

  return (key % table_size);
}

/** Folds a 64-bit integer.
 @return folded value */
UNIV_INLINE
ulint ut_fold_ull(ib_uint64_t d) /*!< in: 64-bit integer */
{
  return (ut_fold_ulint_pair((ulint)d & ULINT32_MASK, (ulint)(d >> 32)));
}

/** Folds a character string ending in the null character.
 @return folded value */
UNIV_INLINE
ulint ut_fold_string(const char *str) /*!< in: null-terminated string */
{
  ulint fold = 0;

  ut_ad(str);

  while (*str != '\0') {
    fold = ut_fold_ulint_pair(fold, (ulint)(*str));
    str++;
  }

  return (fold);
}

/** Folds a pair of ulints.
 @return folded value */
UNIV_INLINE
ulint ut_fold_ulint_pair(ulint n1, /*!< in: ulint */
                         ulint n2) /*!< in: ulint */
{
  return (
      ((((n1 ^ n2 ^ UT_HASH_RANDOM_MASK2) << 8) + n1) ^ UT_HASH_RANDOM_MASK) +
      n2);
}

/** Folds a binary string.
 @return folded value */
UNIV_INLINE
ulint ut_fold_binary(const byte *str, /*!< in: string of bytes */
                     ulint len)       /*!< in: length */
{
  ulint fold = 0;
  const byte *str_end = str + (len & 0xFFFFFFF8);

  ut_ad(str || !len);

  while (str < str_end) {
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
    fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
  }

  switch (len & 0x7) {
    case 7:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
      // Fall through.
    case 6:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
      // Fall through.
    case 5:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
      // Fall through.
    case 4:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
      // Fall through.
    case 3:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
      // Fall through.
    case 2:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
      // Fall through.
    case 1:
      fold = ut_fold_ulint_pair(fold, (ulint)(*str++));
  }

  return (fold);
}