Replace random(), pg_erand48(), etc with a better PRNG API and algorithm.

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

Author: tglsfdc

configure

@@ -16463,32 +16463,6 @@ esac
 
 fi
 
-ac_fn_c_check_func "$LINENO" "random" "ac_cv_func_random"
-if test "x$ac_cv_func_random" = xyes; then :
-  $as_echo "#define HAVE_RANDOM 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" random.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS random.$ac_objext"
- ;;
-esac
-
-fi
-
-ac_fn_c_check_func "$LINENO" "srandom" "ac_cv_func_srandom"
-if test "x$ac_cv_func_srandom" = xyes; then :
-  $as_echo "#define HAVE_SRANDOM 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" srandom.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS srandom.$ac_objext"
- ;;
-esac
-
-fi
-
 ac_fn_c_check_func "$LINENO" "strlcat" "ac_cv_func_strlcat"
 if test "x$ac_cv_func_strlcat" = xyes; then :
   $as_echo "#define HAVE_STRLCAT 1" >>confdefs.h

configure.ac

@@ -1858,8 +1858,6 @@ AC_REPLACE_FUNCS(m4_normalize([
 	mkdtemp
 	pread
 	pwrite
-	random
-	srandom
 	strlcat
 	strlcpy
 	strnlen

contrib/amcheck/verify_nbtree.c

@@ -32,6 +32,7 @@
 #include "catalog/index.h"
 #include "catalog/pg_am.h"
 #include "commands/tablecmds.h"
+#include "common/pg_prng.h"
 #include "lib/bloomfilter.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
@@ -466,8 +467,8 @@ bt_check_every_level(Relation rel, Relation heaprel, bool heapkeyspace,
 		total_pages = RelationGetNumberOfBlocks(rel);
 		total_elems = Max(total_pages * (MaxTIDsPerBTreePage / 3),
 						  (int64) state->rel->rd_rel->reltuples);
-		/* Random seed relies on backend srandom() call to avoid repetition */
-		seed = random();
+		/* Generate a random seed to avoid repetition */
+		seed = pg_prng_uint64(&pg_global_prng_state);
 		/* Create Bloom filter to fingerprint index */
 		state->filter = bloom_create(total_elems, maintenance_work_mem, seed);
 		state->heaptuplespresent = 0;

contrib/auto_explain/auto_explain.c

@@ -16,6 +16,7 @@
 
 #include "access/parallel.h"
 #include "commands/explain.h"
+#include "common/pg_prng.h"
 #include "executor/instrument.h"
 #include "jit/jit.h"
 #include "utils/guc.h"
@@ -275,8 +276,7 @@ explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
 	if (nesting_level == 0)
 	{
 		if (auto_explain_log_min_duration >= 0 && !IsParallelWorker())
-			current_query_sampled = (random() < auto_explain_sample_rate *
-									 ((double) MAX_RANDOM_VALUE + 1));
+			current_query_sampled = (pg_prng_double(&pg_global_prng_state) < auto_explain_sample_rate);
 		else
 			current_query_sampled = false;
 	}

contrib/file_fdw/file_fdw.c

@@ -1188,7 +1188,7 @@ file_acquire_sample_rows(Relation onerel, int elevel,
 				 * Found a suitable tuple, so save it, replacing one old tuple
 				 * at random
 				 */
-				int			k = (int) (targrows * sampler_random_fract(rstate.randstate));
+				int			k = (int) (targrows * sampler_random_fract(&rstate.randstate));
 
 				Assert(k >= 0 && k < targrows);
 				heap_freetuple(rows[k]);

contrib/postgres_fdw/postgres_fdw.c

@@ -5158,7 +5158,7 @@ analyze_row_processor(PGresult *res, int row, PgFdwAnalyzeState *astate)
 		if (astate->rowstoskip <= 0)
 		{
 			/* Choose a random reservoir element to replace. */
-			pos = (int) (targrows * sampler_random_fract(astate->rstate.randstate));
+			pos = (int) (targrows * sampler_random_fract(&astate->rstate.randstate));
 			Assert(pos >= 0 && pos < targrows);
 			heap_freetuple(astate->rows[pos]);
 		}

contrib/tablefunc/tablefunc.c

@@ -36,6 +36,7 @@
 
 #include "access/htup_details.h"
 #include "catalog/pg_type.h"
+#include "common/pg_prng.h"
 #include "executor/spi.h"
 #include "funcapi.h"
 #include "lib/stringinfo.h"
@@ -290,8 +291,8 @@ get_normal_pair(float8 *x1, float8 *x2)
 
 	do
 	{
-		u1 = (float8) random() / (float8) MAX_RANDOM_VALUE;
-		u2 = (float8) random() / (float8) MAX_RANDOM_VALUE;
+		u1 = pg_prng_double(&pg_global_prng_state);
+		u2 = pg_prng_double(&pg_global_prng_state);
 
 		v1 = (2.0 * u1) - 1.0;
 		v2 = (2.0 * u2) - 1.0;

contrib/tsm_system_rows/tsm_system_rows.c

@@ -69,7 +69,7 @@ static BlockNumber system_rows_nextsampleblock(SampleScanState *node, BlockNumbe
 static OffsetNumber system_rows_nextsampletuple(SampleScanState *node,
 												BlockNumber blockno,
 												OffsetNumber maxoffset);
-static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate);
+static uint32 random_relative_prime(uint32 n, pg_prng_state *randstate);
 
 
 /*
@@ -213,25 +213,25 @@ system_rows_nextsampleblock(SampleScanState *node, BlockNumber nblocks)
 		if (sampler->step == 0)
 		{
 			/* Initialize now that we have scan descriptor */
-			SamplerRandomState randstate;
+			pg_prng_state randstate;
 
 			/* If relation is empty, there's nothing to scan */
 			if (nblocks == 0)
 				return InvalidBlockNumber;
 
 			/* We only need an RNG during this setup step */
-			sampler_random_init_state(sampler->seed, randstate);
+			sampler_random_init_state(sampler->seed, &randstate);
 
 			/* Compute nblocks/firstblock/step only once per query */
 			sampler->nblocks = nblocks;
 
 			/* Choose random starting block within the relation */
 			/* (Actually this is the predecessor of the first block visited) */
-			sampler->firstblock = sampler_random_fract(randstate) *
+			sampler->firstblock = sampler_random_fract(&randstate) *
 				sampler->nblocks;
 
 			/* Find relative prime as step size for linear probing */
-			sampler->step = random_relative_prime(sampler->nblocks, randstate);
+			sampler->step = random_relative_prime(sampler->nblocks, &randstate);
 		}
 
 		/* Reinitialize lb */
@@ -317,7 +317,7 @@ gcd(uint32 a, uint32 b)
  * (else return 1).
  */
 static uint32
-random_relative_prime(uint32 n, SamplerRandomState randstate)
+random_relative_prime(uint32 n, pg_prng_state *randstate)
 {
 	uint32		r;
 

contrib/tsm_system_time/tsm_system_time.c

@@ -69,7 +69,7 @@ static BlockNumber system_time_nextsampleblock(SampleScanState *node, BlockNumbe
 static OffsetNumber system_time_nextsampletuple(SampleScanState *node,
 												BlockNumber blockno,
 												OffsetNumber maxoffset);
-static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate);
+static uint32 random_relative_prime(uint32 n, pg_prng_state *randstate);
 
 
 /*
@@ -224,25 +224,25 @@ system_time_nextsampleblock(SampleScanState *node, BlockNumber nblocks)
 		if (sampler->step == 0)
 		{
 			/* Initialize now that we have scan descriptor */
-			SamplerRandomState randstate;
+			pg_prng_state randstate;
 
 			/* If relation is empty, there's nothing to scan */
 			if (nblocks == 0)
 				return InvalidBlockNumber;
 
 			/* We only need an RNG during this setup step */
-			sampler_random_init_state(sampler->seed, randstate);
+			sampler_random_init_state(sampler->seed, &randstate);
 
 			/* Compute nblocks/firstblock/step only once per query */
 			sampler->nblocks = nblocks;
 
 			/* Choose random starting block within the relation */
 			/* (Actually this is the predecessor of the first block visited) */
-			sampler->firstblock = sampler_random_fract(randstate) *
+			sampler->firstblock = sampler_random_fract(&randstate) *
 				sampler->nblocks;
 
 			/* Find relative prime as step size for linear probing */
-			sampler->step = random_relative_prime(sampler->nblocks, randstate);
+			sampler->step = random_relative_prime(sampler->nblocks, &randstate);
 		}
 
 		/* Reinitialize lb and start_time */
@@ -330,7 +330,7 @@ gcd(uint32 a, uint32 b)
  * (else return 1).
  */
 static uint32
-random_relative_prime(uint32 n, SamplerRandomState randstate)
+random_relative_prime(uint32 n, pg_prng_state *randstate)
 {
 	uint32		r;
 

src/backend/access/gin/ginget.c

@@ -16,6 +16,7 @@
 
 #include "access/gin_private.h"
 #include "access/relscan.h"
+#include "common/pg_prng.h"
 #include "miscadmin.h"
 #include "storage/predicate.h"
 #include "utils/datum.h"
@@ -787,7 +788,7 @@ entryLoadMoreItems(GinState *ginstate, GinScanEntry entry,
 	}
 }
 
-#define gin_rand() (((double) random()) / ((double) MAX_RANDOM_VALUE))
+#define gin_rand() pg_prng_double(&pg_global_prng_state)
 #define dropItem(e) ( gin_rand() > ((double)GinFuzzySearchLimit)/((double)((e)->predictNumberResult)) )
 
 /*