this affects at least the case of very long inputs, but may also
affect shorter inputs that become long due to growth while upscaling.
basically, the logic for the circular buffer indices of the initial
base-10^9 digit and the slot one past the final digit, and for
simplicity of the loop logic, assumes an invariant that they're not
equal. the upscale loop, which can increase the length of the
base-10^9 representation, attempted to preserve this invariant, but
was actually only ensuring that the end index did not loop around past
the start index, not that the two never become equal.

the main (only?) effect of this bug was that subsequent logic treats
the excessively long number as having no digits, leading to junk
results.

with this patch, setting _POSIX_SOURCE, or setting _POSIX_C_SOURCE or
_XOPEN_SOURCE to an old version, will bring back the interfaces that
were removed in POSIX 2008 - at least the ones i've covered so far,
which are gethostby*, usleep, and ualarm. if there are other functions
still in widespread use that were removed for which similar changes
would be beneficial, they can be added just like this.

not sure why these were originally omitted..

this function never existed historically; since the float/double
functions it's based on are nonstandard and deprecated, there's really
no justification for its existence except that glibc has it. it can be
added back if there's ever really a need...

linux guarantees ll/sc are always available. on mips1, they will be
emulated by the kernel. thus they are part of the linux mips1 abi and
safe to use.

since this interface is rarely used, it's probably best to lean
towards keeping code size down anyway. one-character needles will
still be found immediately by the initial wcschr call anyway.

optimized to avoid allocation and return lines directly out of the
stream buffer whenever possible.

the strspn call was made for every format specifier and end-of-string,
even though the expected return value was 1-2 for normal usage.
replace with simple loop.

amusingly, this cuts more than 10% off the run time of printf("a"); on
the machine i tested it on.

sadly the same optimization is not possible for snprintf without
duplicating all the pseudo-FILE setup code, which is not worth it.

this is needed to match the underlying "ABI" standards. it's not
really an ABI issue since the binary representations are the same, but
having the wrong type can lead to errors when the type arising from a
difference-of-pointers expression does not match the defined type of
ptrdiff_t. most of the problems affect C++, not C.

there are still some discussions going on about tweaking the code, but
at least thing brings us to the point of having something working in
the repository. hopefully the remaining major hashes (md5,sha) will
follow soon.

some minor changes to how hard-coded sets for thread-related purposes
are handled were also needed, since the old object sizes were not
necessarily sufficient. things have gotten a bit ugly in this area,
and i think a cleanup is in order at some point, but for now the goal
is just to get the code working on all supported archs including mips,
which was badly broken by linux rejecting syscalls with the wrong
sigset_t size.

yet another gratuitous mips incompatibility...

unfortunately, a large portion of programs which call crypt are not
prepared for its failure and do not check that the return value is
non-null before using it. thus, always "succeeding" but giving an
unmatchable hash is reportedly a better behavior than failing on
error.

it was suggested that we could do this the same way as other
implementations and put the null-to-unmatchable translation in the
wrapper rather than the individual crypt modules like crypt_des, but
when i tried to do it, i found it was making the logic in __crypt_r
for keeping track of which hash type we're working with and whether it
succeeded or failed much more complex, and potentially error-prone.
the way i'm doing it now seems to have essentially zero cost, anyway.

exp(inf), exp(-inf), exp(nan) used to raise wrong flags

untested; hopefully it's right now

untested

why does mips have to be gratuitously incompatible in every possible
imaginable way?

since .init and .fini are not .text, the toolchain does not seem to
align them for code by default. this yields random breakage depending
on the object sizes the linker is dealing with.

not heavily tested, but the basics are working. the basic concept is
that the dynamic linker entry point code invokes a pure-PIC (no global
accesses) C function in reloc.h to perform the early GOT relocations
needed to make the dynamic linker itself functional, then invokes
__dynlink like on other archs. since mips uses some ugly arch-specific
hacks to optimize relocating the GOT (rather than just using the
normal DT_REL[A] tables like on other archs), the dynamic linker has
been modified slightly to support calling arch-specific relocation
code in reloc.h.

most of the actual mips-specific behavior was developed by reading the
output of readelf on libc.so and simple executable files. i could not
find good reference information on which relocation types need to be
supported or their semantics, so it's possible that some legitimate
usage cases will not work yet.

this is mainly a development convenience but will also ensure users
building from latest git always get up-to-date arch-specific dynamic
linker code without having to "make clean".