Sample from an array, but disallow the last `historySize` results.

sample.tcc

/* Sample from an array, but disallow the last `historySize` results.
 *
 * \tparam historySize History size.
 * \tparam T Array type.
 * \tparam arraySize Array size.
 *
 * \param a Array.
 *
 * \return Element of `a`.
 */
template <size_t historySize, class T, size_t arraySize>
T sample(T (& a)[arraySize]) {
  thread_local size_t offset {0};
  
  size_t i {(offset + random(historySize, arraySize)) % arraySize};
  size_t j {(offset + historySize) % arraySize};

  T tmp {a[i]};
  a[i] = a[j];
  a[j] = tmp;

  offset = (offset + 1) % arraySize;

  return tmp;
}