1 files changed, 79 insertions, 0 deletions
diff --git a/libmisc/tests/test_rand.c b/libmisc/tests/test_rand.c
new file mode 100644
index 0000000..8076155
--- /dev/null
+++ b/libmisc/tests/test_rand.c
@@ -0,0 +1,79 @@
+/* libmisc/tests/test_rand.c - Tests for <libmisc/rand.h>
+ *
+ * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <stdbool.h>
+#include <setjmp.h>
+
+#include <libmisc/rand.h>
+#include <libmisc/_intercept.h>
+
+#include "test.h"
+
+/* Intercept failures *********************************************************/
+
+#ifndef NDEBUG
+jmp_buf *__catch;
+
+void __lm_abort(void) {
+	if (__catch)
+		longjmp(*__catch, 1);
+	abort();
+}
+
+#define should_abort(cmd) do {                \
+		jmp_buf *old_catch = __catch; \
+		jmp_buf env;                  \
+		__catch = &env;               \
+		if (!setjmp(env)) {           \
+			cmd;                  \
+			__catch = old_catch;  \
+			test_assert(false);   \
+		} else {                      \
+			__catch = old_catch;  \
+		}                             \
+	} while (0);
+#endif
+
+/* Actual tests ***************************************************************/
+
+#define ROUNDS 4096
+#define MAX_SEE_ALL 128
+
+static void test_n(uint64_t cnt) {
+	if (cnt == 0 || cnt > UINT64_C(1)<<63) {
+#ifndef NDEBUG
+		should_abort(rand_uint63n(cnt));
+#else
+		return;
+#endif
+	} else {
+		double sum = 0;
+		bool seen[MAX_SEE_ALL] = {0};
+		for (int i = 0; i < ROUNDS; i++) {
+			uint64_t val = rand_uint63n(cnt);
+			sum += val;
+			test_assert(val < cnt);
+			if (cnt < MAX_SEE_ALL)
+				seen[val] = true;
+		}
+		if (cnt > 1) {
+			test_assert(sum/ROUNDS > 0.45*(cnt-1));
+			test_assert(sum/ROUNDS < 0.55*(cnt-1));
+		}
+		if (cnt < MAX_SEE_ALL) {
+			for (uint64_t i = 0; i < cnt; i++)
+				test_assert(seen[i]);
+		}
+	}
+}
+
+int main() {
+	for (uint8_t i = 0; i < 64; i++)
+		test_n(UINT64_C(1)<<i);
+	for (uint64_t j = 0; j < MAX_SEE_ALL; j++)
+		test_n(j);
+	return 0;
+}