added tool to find xorshift parameters

tools/xorshift.c

@@ -0,0 +1,34 @@
+/*
+Exhaustive search of xorshift parameters
+
+Copyright 2025 Ahmet Inan <inan@aicodix.de>
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv) {
+	if (argc != 2)
+		return 1;
+	int bits = atoi(argv[1]);
+	int mask = (1 << bits) - 1;
+	int seed = 1;
+	for (int a = 1; a < bits; ++a) {
+		for (int b = 1; b < bits; ++b) {
+			for (int c = 1; c < bits; ++c) {
+				int good = 1;
+				for (int y = seed, i = mask; good && i; --i) {
+					y ^= y << a;
+					y &= mask;
+					y ^= y >> b;
+					y ^= y << c;
+					y &= mask;
+					good &= (i == 1) == (y == seed);
+				}
+				if (good)
+					printf("%d %d %d\n", a, b, c);
+			}
+		}
+	}
+	return 0;
+}