Re: [PATCH 07/14] Cleanup: avoid undefined shift operation

On Thu, Dec 28, 2017 at 4:35 PM, Dirk Hohndel dirk@hohndel.org wrote:

    unsigned int signbit = (1 << (n - 1));

•   unsigned int mask = (0xFFFFFFFF << n);
  

•   unsigned int mask;
  

•   // shifting a 32bit constant by more than 31 bits has undefined behavior
  

•   if (n == 32)
  

•           mask = 0;
  

•   else
  

•           mask = (0xFFFFFFFF << n);
  

Ugh. That's ugly.

It's much simpler to just do

unsigned int mask = ~(signbit-1);

instead.

Yes, that mask ends up including the sign bit (the old mask did not), but that doesn't matter for the end result.

Linus