I wrote: > | Careful. As you suggest, let's restrict ourselves to two's complement > | platforms. I would want the compiler to warn if the identity holds for an > | ILP32 machine but not an LP64 machine, even if I'm running on an ILP32. > | But if the two types are going to be the same size everywhere (because one > | is the unsigned modifier of the other) then GCC should not complain.
On Wed, Jan 17, 2007 at 04:59:02PM -0600, Gabriel Dos Reis wrote: > The specific cases I'm concerned about here (and if you have a chance > to build firefox for example, you'll see) is when T and U differ only > in signedness, that is > > T = int, U = unsigned > T = long, U = unsigned long > T = long long, U = unsigned long long > > those have the same value representation bits and there is no way, GCC > can mess up -- except bugs in the compiler itself. > Furthermore, elsewhere (in the overflow thread) it has been suggested > that people should convert to the unsigned variants, do computations there, > and convert back to the signed variants. We have just promised an > invariant that we will hold. Fully agreed.
