git: 1730b5c7916e - main - lib/libc/tests: add unit test for arc4random_uniform()

The branch main has been updated by fuz:

URL: https://cgit.FreeBSD.org/src/commit/?id=1730b5c7916ed249ddc97ebe51117899f9323fbc

commit 1730b5c7916ed249ddc97ebe51117899f9323fbc
Author:     Robert Clausecker <fuz@FreeBSD.org>
AuthorDate: 2024-11-18 12:46:16 +0000
Commit:     Robert Clausecker <fuz@FreeBSD.org>
CommitDate: 2024-12-02 10:41:11 +0000

    lib/libc/tests: add unit test for arc4random_uniform()
    
    The new unit test validates that the range reduction works correctly.
    We do not currently validate that there is no bias as that would take
    too much time and memory for a unit test.
    
    Reviewed by:    cem
    Approved by:    emaste
    Differential Revision:  https://reviews.freebsd.org/D47659
---
 lib/libc/tests/gen/arc4random_test.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/lib/libc/tests/gen/arc4random_test.c b/lib/libc/tests/gen/arc4random_test.c
index e96ebdc6c6ca..79139f29f8fa 100644
--- a/lib/libc/tests/gen/arc4random_test.c
+++ b/lib/libc/tests/gen/arc4random_test.c
@@ -1,5 +1,6 @@
 /*-
  * Copyright (c) 2011 David Schultz
+ * Copyright (c) 2024 Robert Clausecker <fuz@FreeBSD.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -29,6 +30,7 @@
 #include <sys/wait.h>
 #include <errno.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -77,10 +79,34 @@ ATF_TC_BODY(test_arc4random, tc)
 	    "sequences are the same");
 }
 
+/*
+ * Test whether arc4random_uniform() returns a number below the given threshold.
+ * Test with various thresholds.
+ */
+ATF_TC_WITHOUT_HEAD(test_arc4random_uniform);
+ATF_TC_BODY(test_arc4random_uniform, tc)
+{
+	size_t i, j;
+	static const uint32_t thresholds[] = {
+		1, 2, 3, 4, 5, 10, 100, 1000,
+		INT32_MAX, (uint32_t)INT32_MAX + 1,
+		UINT32_MAX - 1000000000, UINT32_MAX - 1000000, UINT32_MAX - 1, 0
+	};
+
+	for (i = 0; thresholds[i] != 0; i++)
+		for (j = 0; j < 10000; j++)
+			ATF_CHECK(arc4random_uniform(thresholds[i]) < thresholds[i]);
+
+	/* for a threshold of zero, just check that we get zero every time */
+	for (j = 0; j < 1000; j++)
+		ATF_CHECK_EQ(0, arc4random_uniform(0));
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
 	ATF_TP_ADD_TC(tp, test_arc4random);
+	ATF_TP_ADD_TC(tp, test_arc4random_uniform);
 
 	return (atf_no_error());
 }