linux-gen: random: improve ODP_RANDOM_BASIC data and random test data

Improve the quality of data generated by and the speed of
odp_random_test_data() and _odp_random_std_data() (used when OpenSSL
random is not enabled).

Signed-off-by: Jere Leppänen <jere.leppanen@nokia.com>
Reviewed-by: Tuomas Taipale <tuomas.taipale@nokia.com>
Reviewed-by: Petri Savolainen <petri.savolainen@nokia.com>

1 files changed, 65 insertions, 29 deletions

diff --git a/platform/linux-generic/odp_random_std.c b/platform/linux-generic/odp_random_std.c
index 3afd049f4..50cd773f2 100644
--- a/platform/linux-generic/odp_random_std.c
+++ b/platform/linux-generic/odp_random_std.c
@@ -4,52 +4,88 @@
  * SPDX-License-Identifier:     BSD-3-Clause
  */
 
-#include <odp_posix_extensions.h>
-#include <stdint.h>
-#include <stdlib.h>
 #include <odp/api/byteorder.h>
 #include <odp/api/cpu.h>
 #include <odp/api/debug.h>
 #include <odp_init_internal.h>
 #include <odp_random_std_internal.h>
+#include <odp_cpu.h>
 
+#include <stdint.h>
 #include <time.h>
 
-/* Assume at least two rand bytes are available and RAND_MAX is power of two - 1 */
-ODP_STATIC_ASSERT(RAND_MAX >= UINT16_MAX, "RAND_MAX too small");
-ODP_STATIC_ASSERT((RAND_MAX & (RAND_MAX + 1ULL))  ==  0, "RAND_MAX not power of two - 1");
+/*
+ * Xorshift64*, adapted from [1], and modified to return only the high 32 bits.
+ *
+ * [1] An experimental exploration of Marsaglia's xorshift generators, scrambled
+ *     Sebastiano Vigna, July 2016.
+ *     http://vigna.di.unimi.it/ftp/papers/xorshift.pdf
+ */
+static inline uint32_t xorshift64s32(uint64_t *x)
+{
+	/* The variable x should be initialized to a nonzero seed. [1] */
+	if (!*x)
+		/*
+		 * 2^64 / phi. As far away as possible from any small integer
+		 * fractions, which the caller might be likely to use for the
+		 * next seed after 0.
+		 */
+		*x = 11400714819323198485ull;
 
-static int32_t _random_data(uint8_t *buf, uint32_t len, uint32_t *seed)
+	*x ^= *x >> 12; /* a */
+	*x ^= *x << 25; /* b */
+	*x ^= *x >> 27; /* c */
+	return (*x * 2685821657736338717ull) >> 32;
+}
+
+static int32_t _random_data(uint8_t *buf, uint32_t len, uint64_t *seed)
 {
-	union {
-		uint32_t rand_word;
-		uint8_t rand_byte[4];
-	} u;
-	uint32_t i = 0, j, k;
-
-	while (i < len) {
-		u.rand_word = rand_r(seed);
-
-		/* Use two least significant bytes */
-		j = ODP_LITTLE_ENDIAN ? 0 : 2;
-		for (k = 0; k < 2 && i < len; i++, j++, k++)
-			*buf++ = u.rand_byte[j];
+	const uint32_t ret = len;
+
+	if (!_ODP_UNALIGNED && ((uintptr_t)buf & 3) && len) {
+		uint32_t r = xorshift64s32(seed);
+
+		if ((uintptr_t)buf & 1) {
+			*(uint8_t *)(uintptr_t)buf = r & 0xff;
+			r >>= 8;
+			buf += 1;
+			len -= 1;
+		}
+
+		if (((uintptr_t)buf & 2) && len >= 2) {
+			*(uint16_t *)(uintptr_t)buf = r & 0xffff;
+			buf += 2;
+			len -= 2;
+		}
+	}
+
+	for (uint32_t i = 0; i < len / 4; i++) {
+		*(uint32_t *)(uintptr_t)buf = xorshift64s32(seed);
+		buf += 4;
 	}
 
-	return len;
+	if (len & 3) {
+		uint32_t r = xorshift64s32(seed);
+
+		if (len & 2) {
+			*(uint16_t *)(uintptr_t)buf = r & 0xffff;
+			r >>= 16;
+			buf += 2;
+		}
+
+		if (len & 1)
+			*(uint8_t *)(uintptr_t)buf = r & 0xff;
+	}
+
+	return ret;
 }
 
 int32_t _odp_random_std_test_data(uint8_t *buf, uint32_t len, uint64_t *seed)
 {
-	uint32_t seed32 = (*seed) & 0xffffffff;
-
-	_random_data(buf, len, &seed32);
-
-	*seed = seed32;
-	return len;
+	return _random_data(buf, len, seed);
 }
 
-static __thread uint32_t this_seed;
+static __thread uint64_t this_seed;
 
 int32_t _odp_random_std_data(uint8_t *buf, uint32_t len)
 {
@@ -59,7 +95,7 @@ int32_t _odp_random_std_data(uint8_t *buf, uint32_t len)
 int _odp_random_std_init_local(void)
 {
 	this_seed = time(NULL);
-	this_seed ^= odp_cpu_id() << 16;
+	this_seed ^= (uint64_t)odp_cpu_id() << 32;
 
 	return 0;
 }