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, 6 insertions, 0 deletions

diff --git a/math/Versions b/math/Versions
index 26e15ce..46b9b87 100644
--- a/math/Versions
+++ b/math/Versions
@@ -639,4 +639,10 @@ libm {
     # No SVID compatible error handling.
     exp10;
   }
+  GLIBC_2.40 {
+    # Functions not involving _Float64x or _Float128, for all configurations.
+    log2p1; log2p1f; log2p1l; log2p1f32; log2p1f64; log2p1f32x;
+    # Functions involving _Float64x or _Float128, for some configurations.
+    log2p1f64x; log2p1f128;
+  }
 }