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, 3 insertions, 0 deletions

diff --git a/math/tgmath.h b/math/tgmath.h
index dbfa92d..d9ee3e3 100644
--- a/math/tgmath.h
+++ b/math/tgmath.h
@@ -874,6 +874,9 @@
 #if __GLIBC_USE (IEC_60559_FUNCS_EXT_C23)
 /* Compute exponent to base ten.  */
 #define exp10(Val) __TGMATH_UNARY_REAL_ONLY (Val, exp10)
+
+/* Return log2(1 + X).  */
+#define log2p1(Val) __TGMATH_UNARY_REAL_ONLY (Val, log2p1)
 #endif