ut0rnd.ic

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/******************************************************************
Random numbers and hashing

(c) 1994, 1995 Innobase Oy

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

extern  ulint    ut_rnd_ulint_counter;

/************************************************************
This is used to set the random number seed. */
UNIV_INLINE
void
ut_rnd_set_seed(
/*============*/
	ulint    seed)           /* in: seed */
{
	ut_rnd_ulint_counter = seed;
}

/************************************************************
The following function generates a series of 'random' ulint integers. */
UNIV_INLINE
ulint
ut_rnd_gen_next_ulint(
/*==================*/
			/* out: the next 'random' number */
	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). */
UNIV_INLINE
ulint
ut_rnd_gen_ulint(void)
/*==================*/
			/* out: the 'random' number */
{
	ulint   rnd;
	ulint	n_bits;

	n_bits = 8 * sizeof(ulint);

	ut_rnd_ulint_counter =
			UT_RND1 * ut_rnd_ulint_counter + UT_RND2;

	rnd = ut_rnd_gen_next_ulint(ut_rnd_ulint_counter);

	return(rnd);
}

/************************************************************
Generates a random integer from a given interval. */
UNIV_INLINE
ulint
ut_rnd_interval(
/*============*/
			/* out: the 'random' number */
	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 + 1)));
}

/*************************************************************
Generates a random iboolean value. */
UNIV_INLINE
ibool
ut_rnd_gen_ibool(void)
/*=================*/
			/* out: the random value */
{
	ulint    x;

	x = ut_rnd_gen_ulint();

	if (((x >> 20) + (x >> 15)) & 1) {

		return(TRUE);
	}

	return(FALSE);
} 

/***********************************************************
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. */
UNIV_INLINE
ulint
ut_hash_ulint(
/*=========*/
				/* out: hash value */
	ulint    key,      	/* in: value to be hashed */
	ulint    table_size) 	/* in: hash table size */
{
	key = key ^ UT_HASH_RANDOM_MASK2;

	return(key % table_size);
}

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

/*****************************************************************
Folds a dulint. */
UNIV_INLINE
ulint
ut_fold_dulint(
/*===========*/
			/* out: folded value */
	dulint	d)	/* in: dulint */
{
	return(ut_fold_ulint_pair(ut_dulint_get_low(d),
						ut_dulint_get_high(d)));
} 

/*****************************************************************
Folds a character string ending in the null character. */
UNIV_INLINE
ulint
ut_fold_string(
/*===========*/
				/* out: folded value */
	const char*	str)	/* in: null-terminated string */	
{
#ifdef UNIV_DEBUG
	ulint	i = 0;
#endif
	ulint	fold = 0;

	ut_ad(str);

	while (*str != '\0') {

#ifdef UNIV_DEBUG
		i++;
		ut_a(i < 100);
#endif

		fold = ut_fold_ulint_pair(fold, (ulint)(*str));
		str++;
	}

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

	ut_ad(str);

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

		str++;
	}

	return(fold);
}