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3804539e48
Standardize on xoroshiro128** as our basic PRNG algorithm, eliminating a bunch of platform dependencies as well as fundamentally-obsolete PRNG code. In addition, this API replacement will ease replacing the algorithm again in future, should that become necessary. xoroshiro128** is a few percent slower than the drand48 family, but it can produce full-width 64-bit random values not only 48-bit, and it should be much more trustworthy. It's likely to be noticeably faster than the platform's random(), depending on which platform you are thinking about; and we can have non-global state vectors easily, unlike with random(). It is not cryptographically strong, but neither are the functions it replaces. Fabien Coelho, reviewed by Dean Rasheed, Aleksander Alekseev, and myself Discussion: https://postgr.es/m/alpine.DEB.2.22.394.2105241211230.165418@pseudo
65 lines
1.9 KiB
C
65 lines
1.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* sampling.h
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* definitions for sampling functions
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*
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* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/sampling.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SAMPLING_H
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#define SAMPLING_H
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#include "common/pg_prng.h"
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#include "storage/block.h" /* for typedef BlockNumber */
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/* Random generator for sampling code */
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extern void sampler_random_init_state(uint32 seed,
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pg_prng_state *randstate);
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extern double sampler_random_fract(pg_prng_state *randstate);
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/* Block sampling methods */
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/* Data structure for Algorithm S from Knuth 3.4.2 */
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typedef struct
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{
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BlockNumber N; /* number of blocks, known in advance */
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int n; /* desired sample size */
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BlockNumber t; /* current block number */
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int m; /* blocks selected so far */
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pg_prng_state randstate; /* random generator state */
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} BlockSamplerData;
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typedef BlockSamplerData *BlockSampler;
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extern BlockNumber BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
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int samplesize, uint32 randseed);
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extern bool BlockSampler_HasMore(BlockSampler bs);
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extern BlockNumber BlockSampler_Next(BlockSampler bs);
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/* Reservoir sampling methods */
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typedef struct
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{
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double W;
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pg_prng_state randstate; /* random generator state */
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} ReservoirStateData;
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typedef ReservoirStateData *ReservoirState;
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extern void reservoir_init_selection_state(ReservoirState rs, int n);
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extern double reservoir_get_next_S(ReservoirState rs, double t, int n);
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/* Old API, still in use by assorted FDWs */
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/* For backwards compatibility, these declarations are duplicated in vacuum.h */
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extern double anl_random_fract(void);
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extern double anl_init_selection_state(int n);
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extern double anl_get_next_S(double t, int n, double *stateptr);
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#endif /* SAMPLING_H */
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