Re: Can I avoid "shift count is negative" warning? (involves template parameter)

[me22 <me22 dot ca at gmail dot com>]

On 03/05/07, John Love-Jensen <eljay@adobe.com> wrote:
> Hi Phil,
>
> You can avoid it by using specialization.
>
> For a 32-bit int, that would be 32 positive, and 32 negative
> specializations.
>
> Maybe a bit much, but it'd work.
>
> HTH,
> --Eljay
I think something like this should work, without needing so many
specializations:

template <int a, bool n = a<0>
struct rshift_by;
template <int a>
struct rshift_by<a, true> {
   static int shift(int b) { return b << -a; }
}
template <int a>
struct rshift_by<a, false> {
   static int shift(int b) { return b >> a; }
}

template <int a>
int shift (int b)
{
 return rshift_by<a>::shift(b);
}

int f()
{
 return shift<1>(1);
 return shift<-1>(1);
}

It also avoids the if branch on the compile-time constant, though GCC
is quite good at optimizing those. (IIRC some other compilers (MSVC)
whine about it, though.)

~ Scott McMurray

P.S. I love how the template syntax gives a<0>, don't you?