From: Linus Torvalds > Sent: 24 April 2022 22:42 > > On Sun, Apr 24, 2022 at 2:37 PM Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > Finally, for the same reason - please don't use ">> 8". Because I do > > not believe that bit 8 is well-defined in your arithmetic. The *sign* > > bit will be, but I'm not convinced bit 8 is. > > Hmm.. I think it's ok. It can indeed overflow in 'char' and change the > sign in bit #7, but I suspect bit #8 is always fine. > > Still, If you want to just extend the sign bit, ">> 31" _is_ the > obvious thing to use (yeah, yeah, properly "sizeof(int)*8-1" or > whatever, you get my drift). Except that right shifts of signed values are UB. In particular it has always been valid to do an unsigned shift right on a 2's compliment negative number. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
