If *l == *r && *l, then by transitivity, *r.

previously:
timersub(&now, t, &diff);

warning: value computed is not used [-Wunused-value]

loop condition was incorrect and confusing and caused an infinite loop
when (broken) applications reaped the pid from a signal handler or
another thread before wordexp's call to waitpid could do so.

when WRDE_NOSPACE is returned, the we_wordv and we_wordc members must
be valid, because the interface contract allows them to return partial
results.

in the case of zero results (due either to resource exhaustion or a
zero-word input) the we_wordv array still should contain a terminating
null pointer and the initial we_offs null pointers. this is impossible
on resource exhaustion, so a correct application must presumably check
for a null pointer in we_wordv; POSIX however seems to ignore the
issue. the previous code may have crashed under this situation.

avoid using exit status to determine if a shell error occurred, since
broken programs may install SIGCHLD handlers which reap all zombies,
including ones that don't belong to them. using clone and __WCLONE
does not seem to work for avoiding this problem since exec resets the
exit signal to SIGCHLD.

instead, the new code uses a dummy word at the beginning of the
shell's output, which is ignored, to determine whether the command was
executed successfully. this also fixes a corner case where a word
string containing zero words was interpreted as a single zero-length
word rather than no words at all. POSIX does not seem to require this
case to be supported anyway, though.

in addition, the new code uses the correct retry idiom for waitpid to
ensure that spurious STOP/CONT signals in the child and/or EINTR in
the parent do not prevent successful wait for the child, and blocks
signals in the child.

* simplify sin_pi(x) (don't care about inexact here, the result is
  inexact anyway, and x is not so small to underflow)
* in lgammal add the previously removed special case for x==1 and
  x==2 (to fix the sign of zero in downward rounding mode)
* only define lgammal on supported long double platforms
* change tgamma so the generated code is a bit smaller

previously these macros wrongly had type double rather than long
double. I see no way an application could detect the error in C99, but
C11's _Generic can trivially detect it.

at the same time, even though these archs do not have excess
precision, the number of decimal places used to represent these
constants has been increased to 21 to be consistent with the decimal
representations used for the DBL_* macros.

this is enough to produce the correct value even if the constant is
interpreted as 80-bit extended precision, which matters on archs with
excess precision (FLT_EVAL_METHOD==2) under at least some
interpretations of the C standard. the shorter representations, while
correct if converted to the nominal precision at translation time,
could produce an incorrect value at extended precision, yielding
results such as (double)DBL_MAX != DBL_MAX.

this should not matter since the reality is that either all the sysv
sem syscalls are individual syscalls, or all of them are multiplexed
on the SYS_ipc syscall (depending on arch). but best to be consistent
anyway.

this is a Linux-specific extension to the sysv semaphore api.

siginfo_t is not available from signal.h when the strict ISO C feature
profile (e.g. passing -std=c99 to gcc without defining any other
feature test macros) is used, but the type is needed to declare
waitid. using sys/wait.h (or any POSIX headers) in strict ISO C mode
is an application bug, but in the interest of compatibility, it's best
to avoid producing gratuitous errors. the simplest fix I could find is
suppressing the declaration of waitid (and also signal.h inclusion,
since it's not needed for anything else) in this case, while still
exposing everything else in sys/wait.h

it's not clear why I originally wrote O_NOFOLLOW into this; I suspect
the reason was with an aim of making the function more general for
mapping partially or fully untrusted files provided by the user.
however, the timezone code already precludes use of absolute or
relative pathnames in suid/sgid programs, and disallows .. in
pathnames which are relative to one of the system timezone locations,
so there is no threat of opening a symlink which is not trusted by
appropriate user. since some users may wish to put symbolic links in
the zoneinfo directories to alias timezones, it seems preferable to
allow this.

the rest of the code is not prepared to handle an empty TZ string, so
falling back to __gmt ("GMT"), just as if TZ had been blank or unset,
is the preferable action.

try+l points to \0, so only one iteration was ever tried.

we need to skip to the second TZif header, which starts at
skip+44, and then skip another header (20 bytes) plus the following
6 32bit values.

if sizeof(time_t) == 8, this code path was missing the correct
offset into the zoneinfo file, using the header magic to do
offset calculations.
the 6 32bit fields to be read start at offset 20.

inet_aton returns a boolean success value, whereas __ipparse returns 0
on success and -1 on failure. also change the conditional in inet_addr
to be consistent with other uses of __ipparse where only negative
values are treated as failure.

now that we're waiting for the exit status of the child process, the
result can be conveyed in the exit status rather than via a pipe.
since the error value might not fit in 7 bits, a table is used to
translate possible meaningful error values to small integers.

I mistakenly assumed that clone without a signal produced processes
that would not become zombies; however, waitpid with __WCLONE is
required to release their pids.

while using "l" unconditionally gave the right behavior due to
matching sizes/representations, it was technically UB and produced
compiler warnings with format string checking.

i386 fenv code checks __hwcap for sse support, but in fesetround the sse
code was unconditionally jumped over after the test so the sse rounding
mode was never set.

The log, log2 and log10 functions share a lot of code and to a lesser
extent log1p too. A small part of the code was kept separately in
__log1p.h, but since it did not capture much of the common code and
it was inlined anyway, it did not solve the issue properly. Now the
log functions have significant code duplication, which may be resolved
later, until then they need to be modified together.

logl, log10l, log2l, log1pl:
* Fix the sign when the return value should be -inf.
* Remove the volatile hack from log10l (seems unnecessary)

log1p, log1pf:
* Change the handling of small inputs: only |x|<2^-53 is special
  (then it is enough to return x with the usual subnormal handling)
  this fixes the sign of log1p(0) in downward rounding.
* Do not handle the k==0 case specially (other than skipping the
  elaborate argument reduction)
* Do not handle 1+x close to power-of-two specially (this code was
  used rarely, did not give much speed up and the precision wasn't
  better than the general)
* Fix the correction term formula (c=1-(u-x) was used incorrectly
  when x<1 but (double)(x+1)==2, this was not a critical issue)
* Use the exact same method for calculating log(1+f) as in log
  (except in log1p the c correction term is added to the result).

log, logf, log10, log10f, log2, log2f:
* Use double_t and float_t consistently.
* Now the first part of log10 and log2 is identical to log (until the
  return statement, hopefully this makes maintainence easier).
* Most special case formulas were removed (close to power-of-two and
  k==0 cases), they increase the code size without providing precision
  or performance benefits (and obfuscate the code).
  Only x==1 is handled specially so in downward rounding mode the
  sign of zero is correct (the general formula happens to give -0).
* For x==0 instead of -1/0.0 or -two54/0.0, return -1/(x*x) to force
  raising the exception at runtime.
* Arg reduction code is changed (slightly simplified)
* The thresholds for arg reduction to [sqrt(2)/2,sqrt(2)] are now
  consistently the [0x3fe6a09e00000000,0x3ff6a09dffffffff] and the
  [0x3f3504f3,0x3fb504f2] intervals for double and float reductions
  respectively (the exact threshold values are not critical)
* Remove the obsolete comment for the FLT_EVAL_METHOD!=0 case in log2f
  (The same code is used for all eval methods now, on i386 slightly
  simpler code could be used, but we have asm there anyway)

all:
* Fix signed int arithmetics (using unsigned for bitmanipulation)
* Fix various comments

despite being marked legacy, this was specified by SUSv3 as part of
the XSI option; only the most recent version of the standard dropped
it. reportedly there's actual code using it.

* parse IPv4 dotted-decimal correctly (without strtoul, no leading zeros)
* disallow single leading ':' in IPv6 address
* allow at most 4 hex digits in IPv6 address (according to RFC 2373)
* have enough hex fields in IPv4 mapped IPv6 address
* disallow leading zeros in IPv4 mapped IPv6 address

* allow at most 4 parts
* bounds check the parts correctly
* disallow leading whitespace and sign
* check the address family before falling back to IPv6

despite being practically deprecated, these functions are still part
of the standard and thus cannot reside in a file that also contains
namespace pollution. this reverts some of the changes made in commit
e40f48a4.

fcntl.h: AT_* is not a reserved namespace so extensions cannot be
exposed by default.

langinfo.h: YESSTR and NOSTR were removed from the standard.

limits.h: NL_NMAX was removed from the standard.

signal.h: the conditional for NSIG was wrongly checking _XOPEN_SOURCE
rather than _BSD_SOURCE. this was purely a mistake; it doesn't even
match the commit message from the commit that added it.

in the case of input that does not match the expected form, the
correct return value is 0, not -1.

as usual, this is needed to avoid fd leaks. as a better solution, the
use of fds could possibly be replaced with mmap and a futex.

this fixes an issue reported by Daniel Thau whereby faccessat with the
AT_EACCESS flag did not work in cases where the process is running
suid or sgid but without root privileges. per POSIX, when the process
does not have "appropriate privileges", setuid changes the euid, not
the real uid, and the target uid must be equal to the current real or
saved uid; if this condition is not met, EPERM results. this caused
the faccessat child process to fail.

using the setreuid syscall rather than setuid works. POSIX leaves it
unspecified whether setreuid can set the real user id to the effective
user id on processes without "appropriate privileges", but Linux
allows this; if it's not allowed, there would be no way for this
function to work.

based on patch by Michael Forney. at the same time, I've changed the
if branch to be more clear, avoiding the comma operator.

the underlying issue is that Linux always returns ERANGE when size is
too short, even when it's zero, rather than returning EINVAL for the
special case of zero as required by POSIX.