The pc_*.c files in this directory are copied from musl libc
(https://git.musl-libc.org/cgit/musl/, src/math/ and src/internal/libm.h),
with the functions renamed to a pc_ prefix. musl as a whole is licensed
under the following standard MIT license:

----------------------------------------------------------------------
Copyright © 2005-2020 Rich Felker, et al.

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
----------------------------------------------------------------------

The math library code (src/math/*) is Copyright © 1993,2004 Sun
Microsystems or Copyright © 2003-2009 Bruce D. Evans and labelled as
such in comments in the individual source files; all have been licensed
under extremely permissive terms (the notices are preserved in each file).

The pc_rank_exp.c and pc_rank_sqrt.c additions are from musl v1.1.15
(src/math/exp.c and sqrt.c), with exported symbols renamed and an unsigned
exponent shift used in sqrt to avoid shifting a negative signed value.
