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, 8 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-opt/nldbl-log2p1.c b/sysdeps/ieee754/ldbl-opt/nldbl-log2p1.c
new file mode 100644
index 0000000000..989c69e3d7
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-opt/nldbl-log2p1.c
@@ -0,0 +1,8 @@
+#include "nldbl-compat.h"
+
+double
+attribute_hidden
+log2p1l (double x)
+{
+  return log2p1 (x);
+}