On 22 Mar 2015, at 22:01, Craig Rodrigues <rodr...@freebsd.org> wrote:
>
>> Volatile is not the solution, it is completely orthogonal. The correct
>> way would be to use unsigned integers, for which wrapping is defined,
>> then convert those back and forth when presenting the results to the
>> user.
>>
>
> OK, converting expr.y to use unsigned integers would require a bit of work.
Note that clang has, for a few releases, had builtins that allow
overflow-checked operations and will generate very efficient code. In
op_times, I believe the following should work:
long long mul;
#if __has_builtin(__builtin_smulll_overflow)
if (__builtin_smulll_overflow(a->u.i, b->u.i, &mul))
errx(ERR_EXIT, "overflow");
#else
mul = a->u.i * b->u.i;
#endif
r = make_integer(mul);
I don't know if recent versions of gcc implement these builtins yet. I think
they were added to clang around 3.4, possibly slightly earlier.
David
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