[libcxx-commits] [PATCH] D143140: [libc++] avoid a GCC -Wsigned-compare warning where time_t is unsigned

[Mark de Wever via Phabricator via libcxx-commits]

Mordante requested changes to this revision.
Mordante added a comment.
This revision now requires changes to proceed.

We want to finish the review queue for libc++ due to moving to GitHub PRs. Do you want to continue this patch or should I finish if for you?



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Comment at: libcxx/src/condition_variable.cpp:66
     _LIBCPP_CONSTEXPR ts_sec ts_sec_max = numeric_limits<ts_sec>::max();
-    if (s.count() < ts_sec_max)
-    {
-        ts.tv_sec = static_cast<ts_sec>(s.count());
-        ts.tv_nsec = static_cast<decltype(ts.tv_nsec)>((d - s).count());
-    }
-    else
-    {
-        ts.tv_sec = ts_sec_max;
-        ts.tv_nsec = giga::num - 1;
+    if ((unsigned long long)s.count() < ts_sec_max) {
+      ts.tv_sec  = static_cast<ts_sec>(s.count());
----------------
yamt wrote:
> Mordante wrote:
> > yamt wrote:
> > > Mordante wrote:
> > > > This is consistent with the next line.
> > > my understanding is that s.count() here is long long.
> > > ts_sec is time_t, which can be narrower. (eg. int)
> > > 
> > Good point, `ts_sec`, might indeed be a smaller type. (There is no guarantee count is long long, but it most likely is.)
> > 
> > I still wonder whether this change fixes anything, in glibc `time_t` is signed
> > https://www.gnu.org/software/libc/manual/html_node/Time-Types.html
> > 
> > Maybe it's safer to cast the result to the common type of these two types, WDYT?
> you are right this is not necessary for glibc.
> 
> however, for other platforms, time_t can be uint32_t, uint64_t, etc.
> cf. https://github.com/apache/nuttx/pull/8201
Maybe we should use `cmp_less` which has solved this issue. We require C++20 for the dylib.


Repository:
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  https://reviews.llvm.org/D143140/new/

https://reviews.llvm.org/D143140