On 05-05-2012 10:23, Era Scarecrow wrote:
On Saturday, 5 May 2012 at 07:10:28 UTC, Alex Rønne Petersen wrote:
Right, but the question was whether the language guarantees what I
described. C and C++ don't, and IMO, we should strive to fix that.
I can't see why it wouldn't, unless the compiler adds in checks and
changes it's behavior or the assembler does it's own quirky magic. The
bit patterns of how they end up are pretty fixed, it's just how we
interpret them.
It all depends. GCC (and thus GDC) can target very exotic architectures
where any assumptions may not, for whatever reason, hold true. This is a
language design issue more than it's a "how does architecture X or
compiler Y work" issue.
An interesting problem with undefined behavior for integer overflow and
underflow in C/C++ is that optimizers are basically free to do anything
with regards to them, and often do whatever is more convenient for them.
I know before when i needed to know if it overflowed and simulated the
carry flag, i ended up using a larger type of int. (This was for a
custom multiple precision unsigned ints)
Of course now that I think about it, if anything ends up using MMX for
it's registers, the rules do change a little. MMX don't overflow if I
remember right, they just cap/truncate to the Max/Min. Since it's
intended more for multimedia... If the compiler uses those, I can't tell
you what would happen.
Right, but it's not so much about what *would* happen as much as it is
about what *should* happen. ;)
--
- Alex
