commit 45342ac49d310d3666381c57f28359b061c1af67
Author: Dmitry Kokorin <dmitry@kokorin.org>
Date:   Wed Nov 30 15:32:54 2016 +0300

    initial implementation of xorshift128 and xorshift128plus

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0c38a97
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+*.o
+*.a
+a.out
+benchmark
+
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..e69de29
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..83c6ca7
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+This repo contains an implementations of [xorshift-family](https://en.wikipedia.org/wiki/Xorshift) random number generators.
diff --git a/benchmark.c b/benchmark.c
new file mode 100644
index 0000000..ea0debd
--- /dev/null
+++ b/benchmark.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <time.h>
+
+#include "xorshift.h"
+
+struct timespec clock_diff(struct timespec start, struct timespec stop)
+{
+	struct timespec diff;
+	if ((stop.tv_nsec-start.tv_nsec) < 0) {
+
+		diff.tv_sec  = stop.tv_sec - start.tv_sec - 1;
+		diff.tv_nsec = 1e9 + stop.tv_nsec - start.tv_nsec;
+
+	} else {
+
+		diff.tv_sec  = stop.tv_sec  - start.tv_sec;
+		diff.tv_nsec = stop.tv_nsec - start.tv_nsec;
+	}
+
+	return diff;
+}
+
+
+#define BENCHMARK(func)												\
+{																	\
+	struct timespec start, stop, diff;								\
+																	\
+	clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start);				\
+																	\
+	for (size_t i = 0; i < 1e9; ++i)								\
+		(void)func();												\
+																	\
+	clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &stop);					\
+	diff = clock_diff(start, stop);									\
+																	\
+	printf("%ld:%ld\n", (long)diff.tv_sec, (long)diff.tv_nsec);		\
+}																	\
+
+
+int main()
+{
+	BENCHMARK(xorshift128);
+	BENCHMARK(xorshift128plus);
+
+	return 0;
+}
diff --git a/xorshift.c b/xorshift.c
new file mode 100644
index 0000000..f3a8882
--- /dev/null
+++ b/xorshift.c
@@ -0,0 +1,54 @@
+#include "xorshift.h"
+
+#include <assert.h>
+#include <string.h>
+
+static uint32_t xorshift128_seed[4]     = {1, 1, 1, 1};
+static uint64_t xorshift128plus_seed[2] = {1, 1};
+
+void set_xorshift128_seed(uint32_t seed[4])
+{
+    for (size_t i = 0; i < 4; ++i) {
+
+        assert(seed[i] != (uint32_t)0);
+        xorshift128_seed[i] = seed[i];
+    }
+}
+
+uint32_t xorshift128()
+{
+    uint32_t t = xorshift128_seed[0];
+
+    t ^= t << 11;
+    t ^= t >> 8;
+
+    xorshift128_seed[0] = xorshift128_seed[1];
+    xorshift128_seed[1] = xorshift128_seed[2];
+    xorshift128_seed[2] = xorshift128_seed[3];
+
+    xorshift128_seed[3] ^= xorshift128_seed[3] >> 19;
+    xorshift128_seed[3] ^= t;
+    return xorshift128_seed[3];
+}
+
+
+void set_xorshift128plus_seed(uint64_t seed[2])
+{
+    for (size_t i = 0; i < 2; ++i) {
+
+        assert(seed[i] != (uint64_t)0);
+        xorshift128plus_seed[i] = seed[i];
+    }
+}
+
+uint64_t xorshift128plus()
+{
+    uint64_t x = xorshift128plus_seed[0];
+    uint64_t const y = xorshift128plus_seed[1];
+
+    xorshift128plus_seed[0] = y;
+    x ^= x << 23;
+    xorshift128plus_seed[1] = x ^ y ^ (x >> 17) ^ (y >> 26);
+
+    return xorshift128plus_seed[1] + y;
+}
diff --git a/xorshift.h b/xorshift.h
new file mode 100644
index 0000000..9e5f3c5
--- /dev/null
+++ b/xorshift.h
@@ -0,0 +1,14 @@
+#ifndef _XORSHIFT_H_
+#define _XORSHIFT_H_
+
+#include <stdint.h>
+
+
+void     set_xorshift128_seed(uint32_t seed[4]);
+uint32_t xorshift128();
+
+void     set_xorshift128plus_seed(uint64_t seed[2]);
+uint64_t xorshift128plus();
+
+
+#endif