# Class LevelsPrefixRDConfig
LevelsPrefixRDConfig allows configuring a Levels RankDictionary that is recommended for fast searching in bidirectional indices.

Defined in | <seqan/index.h>
Signature | `template <typename TSize = size_t, typename TFibre = Alloc<>, unsigned LEVELS = 1, unsigned WORDS_PER_BLOCK = 0> struct LevelsRDConfig<TSize, TFibre, LEVELS, WORDS_PER_BLOCK>;`

## Template Parameters

`TSize` | A data type that can store the length of the input text. Default: `size_t`
`TFibre` | A tag for specialization purposes of the underlying strings. Default: `Alloc<>`
`LEVELS` | The number of levels (1, 2, or 3). The more levels, the lower the space consumption but possibly slight performance decreases. Default: `1`
`WORDS_PER_BLOCK` | The number of popcount operations per rank query. A lower number implies more space for faster runtime. 0 is a shortcut for the size of the alphabet of the RankDictionary. Default: `0`

#### Dox Sources

    /*!
     * @class LevelsPrefixRDConfig
     *
     * @headerfile <seqan/index.h>
     *
     * @brief LevelsPrefixRDConfig allows configuring a @link Levels @endlink
     *        RankDictionary that is recommended for fast searching in bidirectional
     *        indices.
     *
     * @signature template <typename TSize = size_t, typename TFibre = Alloc<>,
     *            unsigned LEVELS = 1, unsigned WORDS_PER_BLOCK = 0> struct
     *            LevelsRDConfig<TSize, TFibre, LEVELS, WORDS_PER_BLOCK>;
     *
     * @tparam TSize A data type that can store the length of the input text.
     *               Default: <tt>size_t</tt>
     * @tparam TFibre A tag for specialization purposes of the underlying strings.
     *                Default: <tt>Alloc<></tt>
     * @tparam LEVELS The number of levels (1, 2, or 3). The more levels, the lower
     *                the space consumption but possibly slight performance
     *                decreases. Default: <tt>1</tt>
     * @tparam WORDS_PER_BLOCK The number of popcount operations per rank query. A
     *                         lower number implies more space for faster runtime. 0
     *                         is a shortcut for the size of the alphabet of the
     *                         RankDictionary. Default: <tt>0</tt>
     */