binary_gap() {
    local _n=$1
    local _bin=""
    if (( _n == 0 )); then
        _bin="0"
    else
        local _x=$_n
        while (( _x > 0 )); do
            _bin="$(( _x % 2 ))$_bin"
            _x=$(( _x / 2 ))
        done
    fi
    _bin="${_bin#"${_bin%%[!0]*}"}"
    _bin="${_bin%"${_bin##*[!0]}"}"
    local _gap=0 _len=0
    local -a _zeros
    IFS='1' read -ra _zeros <<< "$_bin"
    local _z
    for _z in "${_zeros[@]}"; do
        _len=${#_z}
        (( _len > _gap )) && _gap=$_len
    done
    echo "$_gap"
}