1 files changed, 185 insertions, 0 deletions
diff --git a/src/backend/utils/adt/pseudorandomfuncs.c b/src/backend/utils/adt/pseudorandomfuncs.c
new file mode 100644
index 00000000000..8e82c7078c5
--- /dev/null
+++ b/src/backend/utils/adt/pseudorandomfuncs.c
@@ -0,0 +1,185 @@
+/*-------------------------------------------------------------------------
+ *
+ * pseudorandomfuncs.c
+ *	  Functions giving SQL access to a pseudorandom number generator.
+ *
+ * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/adt/pseudorandomfuncs.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <math.h>
+
+#include "common/pg_prng.h"
+#include "miscadmin.h"
+#include "utils/fmgrprotos.h"
+#include "utils/numeric.h"
+#include "utils/timestamp.h"
+
+/* Shared PRNG state used by all the random functions */
+static pg_prng_state prng_state;
+static bool prng_seed_set = false;
+
+/*
+ * initialize_prng() -
+ *
+ *	Initialize (seed) the PRNG, if not done yet in this process.
+ */
+static void
+initialize_prng(void)
+{
+	if (unlikely(!prng_seed_set))
+	{
+		/*
+		 * If possible, seed the PRNG using high-quality random bits. Should
+		 * that fail for some reason, we fall back on a lower-quality seed
+		 * based on current time and PID.
+		 */
+		if (unlikely(!pg_prng_strong_seed(&prng_state)))
+		{
+			TimestampTz now = GetCurrentTimestamp();
+			uint64		iseed;
+
+			/* Mix the PID with the most predictable bits of the timestamp */
+			iseed = (uint64) now ^ ((uint64) MyProcPid << 32);
+			pg_prng_seed(&prng_state, iseed);
+		}
+		prng_seed_set = true;
+	}
+}
+
+/*
+ * setseed() -
+ *
+ *	Seed the PRNG from a specified value in the range [-1.0, 1.0].
+ */
+Datum
+setseed(PG_FUNCTION_ARGS)
+{
+	float8		seed = PG_GETARG_FLOAT8(0);
+
+	if (seed < -1 || seed > 1 || isnan(seed))
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("setseed parameter %g is out of allowed range [-1,1]",
+					   seed));
+
+	pg_prng_fseed(&prng_state, seed);
+	prng_seed_set = true;
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * drandom() -
+ *
+ *	Returns a random number chosen uniformly in the range [0.0, 1.0).
+ */
+Datum
+drandom(PG_FUNCTION_ARGS)
+{
+	float8		result;
+
+	initialize_prng();
+
+	/* pg_prng_double produces desired result range [0.0, 1.0) */
+	result = pg_prng_double(&prng_state);
+
+	PG_RETURN_FLOAT8(result);
+}
+
+/*
+ * drandom_normal() -
+ *
+ *	Returns a random number from a normal distribution.
+ */
+Datum
+drandom_normal(PG_FUNCTION_ARGS)
+{
+	float8		mean = PG_GETARG_FLOAT8(0);
+	float8		stddev = PG_GETARG_FLOAT8(1);
+	float8		result,
+				z;
+
+	initialize_prng();
+
+	/* Get random value from standard normal(mean = 0.0, stddev = 1.0) */
+	z = pg_prng_double_normal(&prng_state);
+	/* Transform the normal standard variable (z) */
+	/* using the target normal distribution parameters */
+	result = (stddev * z) + mean;
+
+	PG_RETURN_FLOAT8(result);
+}
+
+/*
+ * int4random() -
+ *
+ *	Returns a random 32-bit integer chosen uniformly in the specified range.
+ */
+Datum
+int4random(PG_FUNCTION_ARGS)
+{
+	int32		rmin = PG_GETARG_INT32(0);
+	int32		rmax = PG_GETARG_INT32(1);
+	int32		result;
+
+	if (rmin > rmax)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("lower bound must be less than or equal to upper bound"));
+
+	initialize_prng();
+
+	result = (int32) pg_prng_int64_range(&prng_state, rmin, rmax);
+
+	PG_RETURN_INT32(result);
+}
+
+/*
+ * int8random() -
+ *
+ *	Returns a random 64-bit integer chosen uniformly in the specified range.
+ */
+Datum
+int8random(PG_FUNCTION_ARGS)
+{
+	int64		rmin = PG_GETARG_INT64(0);
+	int64		rmax = PG_GETARG_INT64(1);
+	int64		result;
+
+	if (rmin > rmax)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("lower bound must be less than or equal to upper bound"));
+
+	initialize_prng();
+
+	result = pg_prng_int64_range(&prng_state, rmin, rmax);
+
+	PG_RETURN_INT64(result);
+}
+
+/*
+ * numeric_random() -
+ *
+ *	Returns a random numeric value chosen uniformly in the specified range.
+ */
+Datum
+numeric_random(PG_FUNCTION_ARGS)
+{
+	Numeric		rmin = PG_GETARG_NUMERIC(0);
+	Numeric		rmax = PG_GETARG_NUMERIC(1);
+	Numeric		result;
+
+	initialize_prng();
+
+	result = random_numeric(&prng_state, rmin, rmax);
+
+	PG_RETURN_NUMERIC(result);
+}