On Thu, Jun 13, 2024 at 02:12:20PM GMT, Paul Eggert wrote:

Part of the issue here is that GCC and Clang often do a better job of
warning when constants are signed, not unsigned. For example, suppose a
program mistakenly packages termios flags along with three other bits into
an 'unsigned long', with code like this:

  unsigned long
  tagged_pendin (unsigned tag)
  {
    return (PENDIN << 3) | tag;
  }

Since PENDIN is 0x20000000 Clang and GCC by default warn about the mistake,
as the signed integer overflow has undefined behavior. But if PENDIN were
changed to 0x20000000U the behavior would be well-defined, there would be no
warning even with -Wall -Wextra -Wsign-conversion, and the code would
silently behave as if PENDIN were zero, which is not intended.

This is another reason why appending "U" to PENDIN's value would have
drawbacks as well as advantages.

Hmmmm, very interesting point!  I'll have that in mind when doing
bitwise stuff with constants.

-- 
<https://www.alejandro-colomar.es/>