util: move rand_xorshift128plus() to utils

V2: pass the seed to rand_xorshift128plus() so that we can isolate
    its uses.

Reviewed-by: Grazvydas Ignotas <[email protected]>
Reviewed-by: Nicolai Hähnle <[email protected]>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/util/rand_xor.c b/src/util/rand_xor.c
new file mode 100644
index 00000000000..07b4c22ee15
--- /dev/null
+++ b/src/util/rand_xor.c
@@ -0,0 +1,20 @@
+#include "rand_xor.h"
+
+/* Super fast random number generator.
+ *
+ * This rand_xorshift128plus function by Sebastiano Vigna belongs
+ * to the public domain.
+ */
+uint64_t
+rand_xorshift128plus(uint64_t *seed)
+{
+   uint64_t *s = seed;
+
+   uint64_t s1 = s[0];
+   const uint64_t s0 = s[1];
+   s[0] = s0;
+   s1 ^= s1 << 23;
+   s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
+
+   return s[1] + s0;
+}