sqrt should be 0.5ulp precise, but the current implementation is less
precise than that.
The following patch uses the soft-fp code (like e.g. glibc for x86) for it
if possible. I didn't want to replicate the libgcc infrastructure for
choosing the right sfp-machine.h, so the patch just uses a single generic
implementation. As the code is used solely for the finite positive arguments,
it shouldn't generate NaNs (so the exact form of canonical QNaN/SNaN is
irrelevant), and sqrt for these shouldn't produce underflows/overflows either,
for < 1.0 arguments it always returns larger values than the argument and for
> 1.0 smaller values than the argument.
2024-04-09 Jakub Jelinek <jakub@redhat.com>
PR libquadmath/114623
* sfp-machine.h: New file.
* math/sqrtq.c: Include from libgcc/soft-fp also soft-fp.h and quad.h
if possible.
(USE_SOFT_FP): Define in that case.
(sqrtq): Use soft-fp based implementation for the finite positive
arguments if possible.