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-rw-r--r--src/test/test-random-util.c79
1 files changed, 79 insertions, 0 deletions
diff --git a/src/test/test-random-util.c b/src/test/test-random-util.c
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+++ 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);