stdlib: Test for expected sequence of random numbers from rand

As the test comment explains, this test is not quite valid, but
preserving the exact sequences helps distributions to port to
newer glibc versions.  We can remove this test if we ever switch
to a different implementation.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>

diff --git a/stdlib/Makefile b/stdlib/Makefile
index 18a19f46eb369bb53f1b96db7e9fbaec1f9d949d..a5fbc1a27e194656d9dceb0339b5e03805e3425c 100644 (file)
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -296,6 +296,7 @@ tests := \
   tst-qsort3 \
   tst-qsort6 \
   tst-quick_exit \
+  tst-rand-sequence \
   tst-rand48 \
   tst-rand48-2 \
   tst-random \

diff --git a/stdlib/tst-rand-sequence.c b/stdlib/tst-rand-sequence.c
new file mode 100644 (file)
index 0000000..4691dfd
--- /dev/null
+++ b/stdlib/tst-rand-sequence.c
@@ -0,0 +1,57 @@
+/* Test that rand () evaluates to a special expected sequence.
+   Copyright (C) 2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* This test is borderline invalid because the rand function is not
+   guaranteed to produce the same sequence of numbers on every
+   architecture or glibc build.  However, some software packages have
+   test suites that depend on the specific sequence of numbers return
+   here, so this test verifies that they do not change unexpectedly.  */
+
+#include <stdlib.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  TEST_COMPARE (rand (), 1804289383);
+  TEST_COMPARE (rand (), 846930886);
+  TEST_COMPARE (rand (), 1681692777);
+  TEST_COMPARE (rand (), 1714636915);
+  TEST_COMPARE (rand (), 1957747793);
+  TEST_COMPARE (rand (), 424238335);
+  TEST_COMPARE (rand (), 719885386);
+  TEST_COMPARE (rand (), 1649760492);
+  TEST_COMPARE (rand (), 596516649);
+  TEST_COMPARE (rand (), 1189641421);
+
+  srand (1009);
+  TEST_COMPARE (rand (), 176208083);
+  TEST_COMPARE (rand (), 1650100842);
+  TEST_COMPARE (rand (), 1813188575);
+  TEST_COMPARE (rand (), 2064804480);
+  TEST_COMPARE (rand (), 1944264725);
+  TEST_COMPARE (rand (), 1673642853);
+  TEST_COMPARE (rand (), 1582759448);
+  TEST_COMPARE (rand (), 309901569);
+  TEST_COMPARE (rand (), 444031692);
+  TEST_COMPARE (rand (), 1926035991);
+
+  return 0;
+}
+
+#include <support/test-driver.c>