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Refactor prng* from cpp macros into inline functions.

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Remove 32-bit variant, convert prng64() to prng_lg_range(), and add
prng_range().
This commit is contained in:
Jason Evans
2016-02-09 16:28:40 -08:00
committed by Jason Evans
parent c87ab25d18
commit 34676d3369
12 changed files with 205 additions and 69 deletions
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67
include/jemalloc/internal/prng.h
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@@ -18,31 +18,9 @@
* 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 prng32(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 prng32(), but 64 bits of pseudo-randomness, using uint64_t. */
#define prng64(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)
#define PRNG_A UINT64_C(6364136223846793005)
#define PRNG_C UINT64_C(1442695040888963407)
#endif /* JEMALLOC_H_TYPES */
/******************************************************************************/
@@ -56,5 +34,46 @@
/******************************************************************************/
#ifdef JEMALLOC_H_INLINES
#ifndef JEMALLOC_ENABLE_INLINE
uint64_t prng_lg_range(uint64_t *state, unsigned lg_range);
uint64_t prng_range(uint64_t *state, uint64_t range);
#endif
#if (defined(JEMALLOC_ENABLE_INLINE) || defined(JEMALLOC_PRNG_C_))
JEMALLOC_ALWAYS_INLINE uint64_t
prng_lg_range(uint64_t *state, unsigned lg_range)
{
uint64_t ret;
assert(lg_range > 0);
assert(lg_range <= 64);
ret = (*state * PRNG_A) + PRNG_C;
*state = ret;
ret >>= (64 - lg_range);
return (ret);
}
JEMALLOC_ALWAYS_INLINE uint64_t
prng_range(uint64_t *state, uint64_t range)
{
uint64_t ret;
unsigned lg_range;
assert(range > 1);
/* Compute the ceiling of lg(range). */
lg_range = jemalloc_ffsl(pow2_ceil_u64(range)) - 1;
/* Generate a result in [0..range) via repeated trial. */
do {
ret = prng_lg_range(state, lg_range);
} while (ret >= range);
return (ret);
}
#endif
#endif /* JEMALLOC_H_INLINES */
/******************************************************************************/