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, 24 insertions, 0 deletions

diff --git a/sysdeps/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps
index e0015347d0..893c22b19b 100644
--- a/sysdeps/x86_64/fpu/libm-test-ulps
+++ b/sysdeps/x86_64/fpu/libm-test-ulps
@@ -1847,6 +1847,30 @@ float: 1
 Function: "log2_vlen8_avx2":
 float: 1
 
+Function: "log2p1":
+double: 1
+float: 1
+float128: 3
+ldouble: 2
+
+Function: "log2p1_downward":
+double: 2
+float: 2
+float128: 3
+ldouble: 4
+
+Function: "log2p1_towardzero":
+double: 2
+float: 2
+float128: 2
+ldouble: 4
+
+Function: "log2p1_upward":
+double: 1
+float: 2
+float128: 2
+ldouble: 5
+
 Function: "log_downward":
 float: 2
 float128: 1