From c706d194a9161fc49bb8b7cf5e18b1d18d068d88 Mon Sep 17 00:00:00 2001
From: Szabolcs Nagy <nsz@port70.net>
Date: Sat, 3 Aug 2013 02:06:20 +0000
Subject: [PATCH] simple random test (statistical with very low failure
 probability)

---
 src/functional/random.c | 86 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 src/functional/random.c

diff --git a/src/functional/random.c b/src/functional/random.c
new file mode 100644
index 0000000..65bbf28
--- /dev/null
+++ b/src/functional/random.c
@@ -0,0 +1,86 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "test.h"
+
+/* naive statistical checks */
+
+/* error p ~ 1.6e-6 */
+static int chkmissing(long *x)
+{
+	int d[8] = {0};
+	int i;
+	for (i = 0; i < 100; i++)
+		d[x[i]%8]++;
+	for (i = 0; i < 8; i++)
+		if (d[i]==0)
+			return 1;
+	return 0;
+}
+
+/* error p ~ 4e-6 */
+static int chkrepeat(long *x)
+{
+	int i, j;
+	for (i = 0; i < 100; i++)
+		for (j = 0; j < i; j++)
+			if (x[i] == x[j])
+				return 1;
+	return 0;
+}
+
+/* error p ~ 1e-6 */
+static unsigned orx;
+static int chkones(long *x)
+{
+	int i;
+	orx = 0;
+	for (i = 0; i < 20; i++)
+		orx |= x[i];
+	return orx != 0x7fffffff;
+}
+
+void checkseed(unsigned seed, long *x)
+{
+	int i;
+	srandom(seed);
+	for (i = 0; i < 100; i++)
+		x[i] = random();
+	if (chkmissing(x))
+		t_error("weak seed %d, missing pattern in low bits\n", seed);
+	if (chkrepeat(x))
+		t_error("weak seed %d, exact repeats\n", seed);
+	if (chkones(x))
+		t_error("weak seed %d, or pattern: 0x%08x\n", seed, orx);
+}
+
+int main()
+{
+	long x[100];
+	long y,z;
+	int i;
+	char state[128];
+	char *p;
+	char *q;
+
+	for (i = 0; i < 100; i++)
+		x[i] = random();
+	p = initstate(1, state, sizeof state);
+	for (i = 0; i < 100; i++)
+		if (x[i] != (y = random()))
+			t_error("initstate(1) is not default: (%d) default: %ld, seed1: %ld\n", i, x[i], y);
+	for (i = 0; i < 10; i++) {
+		z = random();
+		q = setstate(p);
+		if (z != (y = random()))
+			t_error("setstate failed (%d) orig: %ld, reset: %ld\n", i, z, y);
+		p = setstate(q);
+	}
+	srandom(1);
+	for (i = 0; i < 100; i++)
+		if (x[i] != (y = random()))
+			t_error("srandom(1) is not default: (%d) default: %ld, seed1: %ld\n", i, x[i], y);
+	checkseed(0x7fffffff, x);
+	for (i = 0; i < 10; i++)
+		checkseed(i, x);
+	return t_status;
+}
-- 
2.20.1