[redis.git] / deps / jemalloc / include / jemalloc / internal / prn.h

/******************************************************************************/
#ifdef JEMALLOC_H_TYPES

/*
 * Simple linear congruential pseudo-random number generator:
 *
 *   prn(y) = (a*x + c) % m
 *
 * where the following constants ensure maximal period:
 *
 *   a == Odd number (relatively prime to 2^n), and (a-1) is a multiple of 4.
 *   c == Odd number (relatively prime to 2^n).
 *   m == 2^32
 *
 * See Knuth's TAOCP 3rd Ed., Vol. 2, pg. 17 for details on these constraints.
 *
 * This choice of m has the disadvantage that the quality of the bits is
 * proportional to bit position.  For example. the lowest bit has a cycle of 2,
 * the next has a cycle of 4, etc.  For this reason, we prefer to use the upper
 * bits.
 *
 * Macro parameters:
 *   uint32_t r          : Result.
 *   unsigned lg_range   : (0..32], number of least significant bits to return.
 *   uint32_t state      : Seed value.
 *   const uint32_t a, c : See above discussion.
 */
#define prn32(r, lg_range, state, a, c) do {				\
	assert(lg_range > 0);						\
	assert(lg_range <= 32);						\
									\
	r = (state * (a)) + (c);					\
	state = r;							\
	r >>= (32 - lg_range);						\
} while (false)

/* Same as prn32(), but 64 bits of pseudo-randomness, using uint64_t. */
#define prn64(r, lg_range, state, a, c) do {				\
	assert(lg_range > 0);						\
	assert(lg_range <= 64);						\
									\
	r = (state * (a)) + (c);					\
	state = r;							\
	r >>= (64 - lg_range);						\
} while (false)

#endif /* JEMALLOC_H_TYPES */
/******************************************************************************/
#ifdef JEMALLOC_H_STRUCTS

#endif /* JEMALLOC_H_STRUCTS */
/******************************************************************************/
#ifdef JEMALLOC_H_EXTERNS

#endif /* JEMALLOC_H_EXTERNS */
/******************************************************************************/
#ifdef JEMALLOC_H_INLINES

#endif /* JEMALLOC_H_INLINES */
/******************************************************************************/
Commit	Line	Data
a78e148b	1	/******************************************************************************/
	2	#ifdef JEMALLOC_H_TYPES
	3
	4	/*
	5	* Simple linear congruential pseudo-random number generator:
	6	*
	7	* prn(y) = (a*x + c) % m
	8	*
	9	* where the following constants ensure maximal period:
	10	*
	11	* a == Odd number (relatively prime to 2^n), and (a-1) is a multiple of 4.
	12	* c == Odd number (relatively prime to 2^n).
	13	* m == 2^32
	14	*
	15	* See Knuth's TAOCP 3rd Ed., Vol. 2, pg. 17 for details on these constraints.
	16	*
	17	* This choice of m has the disadvantage that the quality of the bits is
	18	* proportional to bit position. For example. the lowest bit has a cycle of 2,
	19	* the next has a cycle of 4, etc. For this reason, we prefer to use the upper
	20	* bits.
	21	*
	22	* Macro parameters:
	23	* uint32_t r : Result.
	24	* unsigned lg_range : (0..32], number of least significant bits to return.
	25	* uint32_t state : Seed value.
	26	* const uint32_t a, c : See above discussion.
	27	*/
	28	#define prn32(r, lg_range, state, a, c) do { \
	29	assert(lg_range > 0); \
	30	assert(lg_range <= 32); \
	31	\
	32	r = (state * (a)) + (c); \
	33	state = r; \
	34	r >>= (32 - lg_range); \
	35	} while (false)
	36
	37	/* Same as prn32(), but 64 bits of pseudo-randomness, using uint64_t. */
	38	#define prn64(r, lg_range, state, a, c) do { \
	39	assert(lg_range > 0); \
	40	assert(lg_range <= 64); \
	41	\
	42	r = (state * (a)) + (c); \
	43	state = r; \
	44	r >>= (64 - lg_range); \
	45	} while (false)
	46
	47	#endif /* JEMALLOC_H_TYPES */
	48	/******************************************************************************/
	49	#ifdef JEMALLOC_H_STRUCTS
	50
	51	#endif /* JEMALLOC_H_STRUCTS */
	52	/******************************************************************************/
	53	#ifdef JEMALLOC_H_EXTERNS
	54
	55	#endif /* JEMALLOC_H_EXTERNS */
	56	/******************************************************************************/
	57	#ifdef JEMALLOC_H_INLINES
	58
	59	#endif /* JEMALLOC_H_INLINES */
	60	/******************************************************************************/