On 01/12/17 14:34 +0000, Jonathan Wakely wrote:
On 01/12/17 15:22 +0100, Paolo Carlini wrote:
Hi,
On 01/12/2017 15:11, Jonathan Wakely wrote:
On 01/12/17 14:02 +0000, Jonathan Wakely wrote:
Is there a reason we left-shift into the sign bit, causing undefined
behaviour? The approach used in std::numeric_limits seems better.
The current code warns with -Wpedantic -Wsystem-headers:
/usr/include/c++/7/ext/numeric_traits.h:58:35: warning: overflow
in implicit constant conversion [-Woverflow]
static const _Value __min = __glibcxx_min(_Value);
^~~~~~~~~~~~~
Many details can be found in c++/52119. Which should probably be
updated, right?
At the time I handled the libstdc++ side of the issue, and for some
reason forgot to fix at the same time the ext/numeric_traits bits. I
have no idea why, maybe to be conservative, in a way.
Huh, so is the warning wrong? Is it only undefined in C++98?
Oh I see, we actually get a different warning on trunk:
/home/jwakely/gcc/8/include/c++/8.0.0/ext/numeric_traits.h:58:55: warning:
overflow in conversion from ‘int’ to ‘short int’ changes value from ‘32768’ to
‘-32768’ [-Woverflow]
static const _Value __min = __glibcxx_min(_Value);
^
So we just need a cast instead.
