Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 136 insertions, 0 deletions

diff --git a/src/port/erand48.c b/src/port/erand48.c
new file mode 100644
index 0000000..a82ea94
--- /dev/null
+++ b/src/port/erand48.c
@@ -0,0 +1,136 @@
+/*-------------------------------------------------------------------------
+ *
+ * erand48.c
+ *
+ * This file supplies pg_erand48() and related functions, which except
+ * for the names are just like the POSIX-standard erand48() family.
+ * (We don't supply the full set though, only the ones we have found use
+ * for in Postgres.  In particular, we do *not* implement lcong48(), so
+ * that there is no need for the multiplier and addend to be variable.)
+ *
+ * We used to test for an operating system version rather than
+ * unconditionally using our own, but (1) some versions of Cygwin have a
+ * buggy erand48() that always returns zero and (2) as of 2011, glibc's
+ * erand48() is strangely coded to be almost-but-not-quite thread-safe,
+ * which doesn't matter for the backend but is important for pgbench.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ *
+ * Portions Copyright (c) 1993 Martin Birgmeier
+ * All rights reserved.
+ *
+ * You may redistribute unmodified or modified versions of this source
+ * code provided that the above copyright notice and this and the
+ * following conditions are retained.
+ *
+ * This software is provided ``as is'', and comes with no warranties
+ * of any kind. I shall in no event be liable for anything that happens
+ * to anyone/anything when using this software.
+ *
+ * IDENTIFICATION
+ *	  src/port/erand48.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+#include <math.h>
+
+/* These values are specified by POSIX */
+#define RAND48_MULT		UINT64CONST(0x0005deece66d)
+#define RAND48_ADD		UINT64CONST(0x000b)
+
+/* POSIX specifies 0x330e's use in srand48, but the other bits are arbitrary */
+#define RAND48_SEED_0	(0x330e)
+#define RAND48_SEED_1	(0xabcd)
+#define RAND48_SEED_2	(0x1234)
+
+static unsigned short _rand48_seed[3] = {
+	RAND48_SEED_0,
+	RAND48_SEED_1,
+	RAND48_SEED_2
+};
+
+
+/*
+ * Advance the 48-bit value stored in xseed[] to the next "random" number.
+ *
+ * Also returns the value of that number --- without masking it to 48 bits.
+ * If caller uses the result, it must mask off the bits it wants.
+ */
+static uint64
+_dorand48(unsigned short xseed[3])
+{
+	/*
+	 * We do the arithmetic in uint64; any type wider than 48 bits would work.
+	 */
+	uint64		in;
+	uint64		out;
+
+	in = (uint64) xseed[2] << 32 | (uint64) xseed[1] << 16 | (uint64) xseed[0];
+
+	out = in * RAND48_MULT + RAND48_ADD;
+
+	xseed[0] = out & 0xFFFF;
+	xseed[1] = (out >> 16) & 0xFFFF;
+	xseed[2] = (out >> 32) & 0xFFFF;
+
+	return out;
+}
+
+
+/*
+ * Generate a random floating-point value using caller-supplied state.
+ * Values are uniformly distributed over the interval [0.0, 1.0).
+ */
+double
+pg_erand48(unsigned short xseed[3])
+{
+	uint64		x = _dorand48(xseed);
+
+	return ldexp((double) (x & UINT64CONST(0xFFFFFFFFFFFF)), -48);
+}
+
+/*
+ * Generate a random non-negative integral value using internal state.
+ * Values are uniformly distributed over the interval [0, 2^31).
+ */
+long
+pg_lrand48(void)
+{
+	uint64		x = _dorand48(_rand48_seed);
+
+	return (x >> 17) & UINT64CONST(0x7FFFFFFF);
+}
+
+/*
+ * Generate a random signed integral value using caller-supplied state.
+ * Values are uniformly distributed over the interval [-2^31, 2^31).
+ */
+long
+pg_jrand48(unsigned short xseed[3])
+{
+	uint64		x = _dorand48(xseed);
+
+	return (int32) ((x >> 16) & UINT64CONST(0xFFFFFFFF));
+}
+
+/*
+ * Initialize the internal state using the given seed.
+ *
+ * Per POSIX, this uses only 32 bits from "seed" even if "long" is wider.
+ * Hence, the set of possible seed values is smaller than it could be.
+ * Better practice is to use caller-supplied state and initialize it with
+ * random bits obtained from a high-quality source of random bits.
+ *
+ * Note: POSIX specifies a function seed48() that allows all 48 bits
+ * of the internal state to be set, but we don't currently support that.
+ */
+void
+pg_srand48(long seed)
+{
+	_rand48_seed[0] = RAND48_SEED_0;
+	_rand48_seed[1] = (unsigned short) seed;
+	_rand48_seed[2] = (unsigned short) (seed >> 16);
+}