/*!
* \param i The exclusive index of the prefix range [0..i-1], so \f$i\in[0..size()]\f$.
* \param c The symbol to count the occurrences in the prefix.
* \return The number of occurrences of symbol c in the prefix [0..i-1] of the supported vector.
* \par Time complexity
* \f$ \Order{H_0} \f$ on average, where \f$ H_0 \f$ is the zero order entropy of
* the sequence
*/
size_type rank(size_type i, value_type c)const {
assert(i <= size());
if (i == 0)
return 0;
size_type wt_ex_pos = m_bl_rank(i);
size_type c_runs = m_wt.rank(wt_ex_pos, c);
if (c_runs == 0)
return 0;
if (m_wt[wt_ex_pos-1] == c) {
size_type c_run_begin = m_bl_select(wt_ex_pos);
return m_bf_select(m_C_bf_rank[c] + c_runs) - m_C[c] + i - c_run_begin;
} else {
return m_bf_select(m_C_bf_rank[c] + c_runs + 1) - m_C[c];
}
};
