boost::container::small_vector invalid internal capacity

[DirtY.iCE.hu@…]

Sometimes the internal capacity of the small_vector is smaller than the specified. Take the following example:

#include <boost/container/small_vector.hpp>
#include <iostream>

int main()
{
  boost::container::small_vector<char, 15> v{ 0 };
  boost::container::small_vector<char, 15> v2(15);
  std::cout << &v << ' ' << (void*)&v[0] << ' ' << v.capacity() << ' '
            << decltype(v)::static_capacity << '\n';
  std::cout << &v2 << " " << (void*)&v2[0] << ' ' << v2.capacity() << ' '
            << decltype(v2)::static_capacity << '\n';
}

Output on amd64 linux (with clang 4.0.1, but gcc exhibits the same behavior):

0x7ffe053c4700 0x7ffe053c4718 8 15
0x7ffe053c46c8 0xbbfc20 23 15

On 32-bit (-m32):

0xffdfecb0 0xffdfecbc 12 15          
0xffdfec88 0x86aea10 27 15

Even though the capacity should be 15, it's 8 on 64-bit and 12 on 32-bit, while static_capacity reports 15. When actually trying to put 15 elements into the vector, it allocates memory from heap.