[PATCH 2/2] stdlib: Test for expected sequence of random numbers from rand

[Noah Goldstein]

On Mon, Jan 20, 2025 at 2:07 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> 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.
> ---
>  stdlib/Makefile            |  1 +
>  stdlib/tst-rand-sequence.c | 57 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 58 insertions(+)
>  create mode 100644 stdlib/tst-rand-sequence.c
>
> diff --git a/stdlib/Makefile b/stdlib/Makefile
> index 18a19f46eb..a5fbc1a27e 100644
> --- 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
> index 0000000000..4691dfd1e7
> --- /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>
> --
> 2.48.1
>

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