Implement C23 log2p1

C23 adds various <math.h> function families originally defined in TS
18661-4.  Add the log2p1 functions (log2(1+x): like log1p, but for
base-2 logarithms).

This illustrates the intended structure of implementations of all
these function families: define them initially with a type-generic
template implementation.  If someone wishes to add type-specific
implementations, it is likely such implementations can be both faster
and more accurate than the type-generic one and can then override it
for types for which they are implemented (adding benchmarks would be
desirable in such cases to demonstrate that a new implementation is
indeed faster).

The test inputs are copied from those for log1p.  Note that these
changes make gen-auto-libm-tests depend on MPFR 4.2 (or later).

The bulk of the changes are fairly generic for any such new function.
(sysdeps/powerpc/nofpu/Makefile only needs changing for those
type-generic templates that use fabs.)

Tested for x86_64 and x86, and with build-many-glibcs.py.

1 files changed, 53 insertions, 0 deletions

diff --git a/math/libm-test-log2p1.inc b/math/libm-test-log2p1.inc
new file mode 100644
index 0000000000..62df95903d
--- /dev/null
+++ b/math/libm-test-log2p1.inc
@@ -0,0 +1,53 @@
+/* Test log2p1.
+   Copyright (C) 2024 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/>.  */
+
+#include "libm-test-driver.c"
+
+static const struct test_f_f_data log2p1_test_data[] =
+  {
+    TEST_f_f (log2p1, -1, minus_infty, DIVIDE_BY_ZERO_EXCEPTION|ERRNO_ERANGE),
+    TEST_f_f (log2p1, -2, qnan_value, INVALID_EXCEPTION|ERRNO_EDOM),
+    TEST_f_f (log2p1, -max_value, qnan_value, INVALID_EXCEPTION|ERRNO_EDOM|XFAIL_ROUNDING_IBM128_LIBGCC),
+    TEST_f_f (log2p1, minus_infty, qnan_value, INVALID_EXCEPTION|ERRNO_EDOM),
+
+    TEST_f_f (log2p1, plus_infty, plus_infty, ERRNO_UNCHANGED),
+    TEST_f_f (log2p1, qnan_value, qnan_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_f (log2p1, -qnan_value, qnan_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_f (log2p1, snan_value, qnan_value, INVALID_EXCEPTION),
+    TEST_f_f (log2p1, -snan_value, qnan_value, INVALID_EXCEPTION),
+
+    AUTO_TESTS_f_f (log2p1),
+  };
+
+static void
+log2p1_test (void)
+{
+  ALL_RM_TEST (log2p1, 0, log2p1_test_data, RUN_TEST_LOOP_f_f, END);
+}
+
+static void
+do_test (void)
+{
+  log2p1_test ();
+}
+
+/*
+ * Local Variables:
+ * mode:c
+ * End:
+ */