sys: random: add xorshift prng

sys/random/xorshift.c

@@ -0,0 +1,71 @@
+/**
+ * Copyright (C) 2017 Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ *
+ * Code taken from Wikipedia (https://en.wikipedia.org/wiki/Xorshift)
+ */
+
+ /**
+ * @ingroup sys_random
+ * @{
+ * @file
+ *
+ * @brief   Xorshift random number generator implementation
+ *
+ * @author Kaspar Schleiser <kaspar@schleiser.de>
+ * @}
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+
+#include "random.h"
+
+/* The state word must be initialized to non-zero */
+uint32_t xorshift32(uint32_t *state)
+{
+    uint32_t x = *state;
+
+    x ^= x << 13;
+    x ^= x >> 17;
+    x ^= x << 5;
+    *state = x;
+
+    return x;
+}
+
+/* The state array must be initialized to not be all zero */
+uint32_t xorshift128(uint32_t *state)
+{
+    uint32_t t = state[3];
+
+    t ^= t << 11;
+    t ^= t >> 8;
+    state[3] = state[2];
+    state[2] = state[1];
+    state[1] = state[0];
+    t ^= state[0];
+    t ^= state[0] >> 19;
+    state[0] = t;
+
+    return t;
+}
+
+static uint32_t _state32;
+
+uint32_t random_uint32(void)
+{
+    return xorshift32(&_state32);
+}
+
+void random_init(uint32_t val)
+{
+    printf("random init %u\n", (unsigned)val);
+    if (!val) {
+        val = 1;
+    }
+    _state32 = val;
+}