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

3 files changed, 8 insertions, 7 deletions

diff --git a/src/test/modules/test_bloomfilter/test_bloomfilter.c b/src/test/modules/test_bloomfilter/test_bloomfilter.c
index 96c50114286..7109f0476c4 100644
--- a/src/test/modules/test_bloomfilter/test_bloomfilter.c
+++ b/src/test/modules/test_bloomfilter/test_bloomfilter.c
@@ -12,6 +12,7 @@
  */
 #include "postgres.h"
 
+#include "common/pg_prng.h"
 #include "fmgr.h"
 #include "lib/bloomfilter.h"
 #include "miscadmin.h"
@@ -83,9 +84,8 @@ create_and_test_bloom(int power, int64 nelements, int callerseed)
 	 * Generate random seed, or use caller's.  Seed should always be a
 	 * positive value less than or equal to PG_INT32_MAX, to ensure that any
 	 * random seed can be recreated through callerseed if the need arises.
-	 * (Don't assume that RAND_MAX cannot exceed PG_INT32_MAX.)
 	 */
-	seed = callerseed < 0 ? random() % PG_INT32_MAX : callerseed;
+	seed = callerseed < 0 ? pg_prng_int32p(&pg_global_prng_state) : callerseed;
 
 	/* Create Bloom filter, populate it, and report on false positive rate */
 	filter = bloom_create(nelements, bloom_work_mem, seed);
diff --git a/src/test/modules/test_integerset/test_integerset.c b/src/test/modules/test_integerset/test_integerset.c
index 21c6f49b378..58ffff89b38 100644
--- a/src/test/modules/test_integerset/test_integerset.c
+++ b/src/test/modules/test_integerset/test_integerset.c
@@ -12,6 +12,7 @@
  */
 #include "postgres.h"
 
+#include "common/pg_prng.h"
 #include "fmgr.h"
 #include "lib/integerset.h"
 #include "miscadmin.h"
@@ -248,8 +249,7 @@ test_pattern(const test_spec *spec)
 		 * only a small part of the integer space is used.  We would very
 		 * rarely hit values that are actually in the set.
 		 */
-		x = (pg_lrand48() << 31) | pg_lrand48();
-		x = x % (last_int + 1000);
+		x = pg_prng_uint64_range(&pg_global_prng_state, 0, last_int + 1000);
 
 		/* Do we expect this value to be present in the set? */
 		if (x >= last_int)
@@ -571,7 +571,7 @@ test_huge_distances(void)
 	 */
 	while (num_values < 1000)
 	{
-		val += pg_lrand48();
+		val += pg_prng_uint32(&pg_global_prng_state);
 		values[num_values++] = val;
 	}
 
diff --git a/src/test/modules/test_rbtree/test_rbtree.c b/src/test/modules/test_rbtree/test_rbtree.c
index 713ebd1b26d..646c6e42fa8 100644
--- a/src/test/modules/test_rbtree/test_rbtree.c
+++ b/src/test/modules/test_rbtree/test_rbtree.c
@@ -13,6 +13,7 @@
 
 #include "postgres.h"
 
+#include "common/pg_prng.h"
 #include "fmgr.h"
 #include "lib/rbtree.h"
 #include "utils/memutils.h"
@@ -108,7 +109,7 @@ GetPermutation(int size)
 	 */
 	for (i = 1; i < size; i++)
 	{
-		int			j = random() % (i + 1);
+		int			j = pg_prng_uint64_range(&pg_global_prng_state, 0, i);
 
 		if (j < i)				/* avoid fetching undefined data if j=i */
 			permutation[i] = permutation[j];
@@ -320,7 +321,7 @@ testdelete(int size, int delsize)
 
 	for (i = 0; i < delsize; i++)
 	{
-		int			k = random() % size;
+		int			k = pg_prng_uint64_range(&pg_global_prng_state, 0, size - 1);
 
 		while (chosen[k])
 			k = (k + 1) % size;