initial implementation of xorshift128 and xorshift128plus

.gitignore

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+*.o
+*.a
+a.out
+benchmark
+

README.md

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+This repo contains an implementations of [xorshift-family](https://en.wikipedia.org/wiki/Xorshift) random number generators.

benchmark.c

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+#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;
+}

xorshift.c

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+#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;
+}

xorshift.h

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+#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