* Victor Bazarov:
> Alf P. Steinbach wrote:
>> * andrey.vul@gmail.com:
>>> I'm tryin to convert this:
>>> long sumOfBits(int n) {
>>> long x = 0;
>>> int i;
>>> for (i = n - 1; i >= 0; i--)
>>> x += (1 << i);
>>> return x;
>>> }
>>>
>>> into something like this:
>>> template <int n> struct sumOfBits {
>>> static const unsigned char u8value = (unsigned char)((1 << n) +
>>> sumOfBits<n - 1>::u8value);
>>> static const unsigned __int16 u16value = (unsigned __int16)((1 << n)
>>> + sumOfBits<n - 1>::u16value);
>>> static const unsigned __int32 u32value = (unsigned __int32)((1 << n)
>>> + sumOfBits<n - 1>::u32value);
>>> static const unsigned __int64 u64value = (unsigned __int64)((1 << n)
>>> + sumOfBits<n - 1>::u64value);
>>> };
>>> template <> struct sumOfBits <0> {
>>> static const unsigned char u8value = (unsigned char)1;
>>> static const unsigned __int16 u16value = (unsigned __int16)1;
>>> static const unsigned __int32 u32value = (unsigned __int32)1;
>>> static const unsigned __int64 u64value = (unsigned __int64)1;
>>> };
>>>
>>> and so far, all expansions, that have multiples of 8 (8, 16, 32, 64)
>>> return 0 due to overflow.
>>> Any way to correctly rewrite the template?
>> Off the cuff, to reproduce the behavior of the original non-tempalte
>> function:
>>
>> template< int n >
>> struct SumOfBits
>> {
>> enum{ value = (1L << (n-1)) | ((1L << (n-1)) - 1) };
>> };
>
> Well, the loop is uncalled for, so you're, right, it could just be
>
> template<unsigned n>
> struct SumOfBits
> {
> enum { value = (1 << n) - 1 }; // no need to OR anything
> };

I believe this latter version has Undefined Behavior in the case of n =
number of bits in int. Also, the original functions had long result.

Cheers,

- Alf

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