1 files changed, 79 insertions, 0 deletions
diff --git a/src/test/test-random-util.c b/src/test/test-random-util.c
new file mode 100644
index 0000000..e597271
--- /dev/null
+++ b/src/test/test-random-util.c
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <math.h>
+
+#include "hexdecoct.h"
+#include "log.h"
+#include "memory-util.h"
+#include "random-util.h"
+#include "terminal-util.h"
+#include "tests.h"
+
+TEST(random_bytes) {
+        uint8_t buf[16] = {};
+
+        for (size_t i = 1; i < sizeof buf; i++) {
+                random_bytes(buf, i);
+                if (i + 1 < sizeof buf)
+                        assert_se(buf[i] == 0);
+
+                hexdump(stdout, buf, i);
+        }
+}
+
+TEST(crypto_random_bytes) {
+        uint8_t buf[16] = {};
+
+        for (size_t i = 1; i < sizeof buf; i++) {
+                assert_se(crypto_random_bytes(buf, i) == 0);
+                if (i + 1 < sizeof buf)
+                        assert_se(buf[i] == 0);
+
+                hexdump(stdout, buf, i);
+        }
+}
+
+#define TOTAL 100000
+
+static void test_random_u64_range_one(unsigned mod) {
+        log_info("/* %s(%u) */", __func__, mod);
+
+        unsigned max = 0, count[mod];
+        zero(count);
+
+        for (unsigned i = 0; i < TOTAL; i++) {
+                uint64_t x;
+
+                x = random_u64_range(mod);
+
+                count[x]++;
+                max = MAX(max, count[x]);
+        }
+
+        /* Print histogram: vertical axis — value, horizontal axis — count.
+         *
+         * The expected value is always TOTAL/mod, because the distribution should be flat. The expected
+         * variance is TOTAL×p×(1-p), where p==1/mod, and standard deviation the root of the variance.
+         * Assert that the deviation from the expected value is less than 6 standard deviations.
+         */
+        unsigned scale = 2 * max / (columns() < 20 ? 80 : columns() - 20);
+        double exp = (double) TOTAL / mod;
+
+        for (size_t i = 0; i < mod; i++) {
+                double dev = (count[i] - exp) / sqrt(exp * (mod > 1 ? mod - 1 : 1) / mod);
+                log_debug("%02zu: %5u (%+.3f)%*s",
+                          i, count[i], dev,
+                          (int) (count[i] / scale), "x");
+
+                assert_se(fabs(dev) < 6); /* 6 sigma is excessive, but this check should be enough to
+                                           * identify catastrophic failure while minimizing false
+                                           * positives. */
+        }
+}
+
+TEST(random_u64_range) {
+        for (unsigned mod = 1; mod < 29; mod++)
+                test_random_u64_range_one(mod);
+}
+
+DEFINE_TEST_MAIN(LOG_DEBUG);