Implement C23 powr

C23 adds various <math.h> function families originally defined in TS
18661-4.  Add the powr functions, which are like pow, but with simpler
handling of special cases (based on exp(y*log(x)), so negative x and
0^0 are domain errors, powers of -0 are always +0 or +Inf never -0 or
-Inf, and 1^+-Inf and Inf^0 are also domain errors, while NaN^0 and
1^NaN are NaN).  The test inputs are taken from those for pow, with
appropriate adjustments (including removing all tests that would be
domain errors from those in auto-libm-test-in and adding some more
such tests in libm-test-powr.inc).

The underlying implementation uses __ieee754_pow functions after
dealing with all special cases that need to be handled differently.
It might be a little faster (avoiding a wrapper and redundant checks
for special cases) to have an underlying implementation built
separately for both pow and powr with compile-time conditionals for
special-case handling, but I expect the benefit of that would be
limited given that both functions will end up needing to use the same
logic for computing pow outside of special cases.

My understanding is that powr(negative, qNaN) should raise "invalid":
that the rule on "invalid" for an argument outside the domain of the
function takes precedence over a quiet NaN argument producing a quiet
NaN result with no exceptions raised (for rootn it's explicit that the
0th root of qNaN raises "invalid").  I've raised this on the WG14
reflector to confirm the intent.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/math/Makefile b/math/Makefile
index b1d7c767f7..64d9d4d1e5 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -139,6 +139,7 @@ gen-libm-calls = \
   s_log2p1F \
   s_nanF \
   s_nextdownF \
+  s_powrF \
   s_rsqrtF \
   s_significandF \
   s_sinpiF \
@@ -685,6 +686,7 @@ libm-test-funcs-auto = \
   log1p \
   log2p1 \
   pow \
+  powr \
   rsqrt \
   sin \
   sincos \
@@ -1016,6 +1018,7 @@ tgmath3-macros = \
   nexttoward \
   nextup \
   pow \
+  powr \
   remainder \
   remquo \
   rint \
@@ -1439,6 +1442,7 @@ CFLAGS-s_nexttoward.c += -fno-builtin-nexttoward -fno-builtin-nexttowardl
 CFLAGS-s_nexttowardf.c += -fno-builtin-nexttowardf
 CFLAGS-s_nextup.c += -fno-builtin-nextupl
 CFLAGS-e_pow.c += -fno-builtin-powl
+CFLAGS-s_powr.c += -fno-builtin-powrl
 CFLAGS-w_remainder.c += -fno-builtin-remainderl -fno-builtin-dreml
 CFLAGS-s_remquo.c += -fno-builtin-remquol
 CFLAGS-s_rint.c += -fno-builtin-rintl
@@ -1574,6 +1578,7 @@ CFLAGS-s_nextafter.c += -fno-builtin-nextafterf32x -fno-builtin-nextafterf64
 CFLAGS-s_nextdown.c += -fno-builtin-nextdownf32x -fno-builtin-nextdownf64
 CFLAGS-s_nextup.c += -fno-builtin-nextupf32x -fno-builtin-nextupf64
 CFLAGS-e_pow.c += -fno-builtin-powf32x -fno-builtin-powf64
+CFLAGS-s_powr.c += -fno-builtin-powrf32x -fno-builtin-powrf64
 CFLAGS-w_remainder.c += -fno-builtin-remainderf32x -fno-builtin-remainderf64
 CFLAGS-s_remquo.c += -fno-builtin-remquof32x -fno-builtin-remquof64
 CFLAGS-s_rint.c += -fno-builtin-rintf32x -fno-builtin-rintf64
@@ -1700,6 +1705,7 @@ CFLAGS-s_nextafterf.c += -fno-builtin-nextafterf32
 CFLAGS-s_nextdownf.c += -fno-builtin-nextdownf32
 CFLAGS-s_nextupf.c += -fno-builtin-nextupf32
 CFLAGS-e_powf.c += -fno-builtin-powf32
+CFLAGS-s_powrf.c += -fno-builtin-powrf32
 CFLAGS-w_remainderf.c += -fno-builtin-remainderf32
 CFLAGS-s_remquof.c += -fno-builtin-remquof32
 CFLAGS-s_rintf.c += -fno-builtin-rintf32