text: /**
   * @file   reduce_type_width_filter.h
   *
   * @section LICENSE
   *
   * The MIT License
   *
   * @copyright Copyright (c) 2017-2021 TileDB, Inc.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   *
   * @section DESCRIPTION
   *
   * This file declares class BitWidthReductionFilter.
   */
  
  #ifndef TILEDB_BIT_WIDTH_REDUCTION_FILTER_H
  #define TILEDB_BIT_WIDTH_REDUCTION_FILTER_H
  
  #include "tiledb/common/status.h"
  #include "tiledb/sm/filter/filter.h"
  
  using namespace tiledb::common;
  
  namespace tiledb {
  namespace sm {
  
  /**
   * A filter that compresses an array of unsigned integers by reducing the number
   * of bits per element if possible.
   *
   * When compressing, the filter determines the min and max values of the input
   * elements within a window of size N. If the range of values can be represented
   * by an integer of a smaller width, the input elements in the window are
   * transformed to the smaller width and written to the output. Else, the input
   * elements are written to the output unmodified.
   *
   * Within a window, all elements are treated relative to the first input
   * element, which helps in cases of e.g. values that are large but involve
   * relatively small value changes over the window.
   *
   * If the input comes in multiple FilterBuffer parts, each part is broken up
   * into windows separately in the forward direction.
   *
   * Input metadata is not compressed or modified.
   *
   * The forward output metadata has the format:
   *   uint32_t - Original input number of bytes
   *   uint32_t - Number of windows
   *   window0_md
   *   ...
   *   windowN_md
   * Where each window*_md has the fixed format:
   *   T - Window value offset
   *   uint8_t - Bit width of reduced element type T'
   *   uint32_t - Number of bytes in window data
   *
   * The forward output data format is the concatenated window data:
   *   uint8_t[] - Window0 data (possibly-reduced width elements)
   *   uint8_t[] - Window1 data (possibly-reduced width elements)
   *   ...
   *   uint8_t[] - WindowN data (possibly-reduced width elements)
   *
   * The reverse output format is simply:
   *   T[] - Array of original elements
   */
  class BitWidthReductionFilter : public Filter {
   public:
    /** Constructor. */
    BitWidthReductionFilter();
  
    /** Dumps the filter details in ASCII format in the selected output. */
    void dump(FILE* out) const override;
  
    /** Return the max window size used by the filter. */
    uint32_t max_window_size() const;
  
    /**
     * Reduce the bit size of the given input into the given output.
     */
    Status run_forward(
        const Tile& tile,
        FilterBuffer* input_metadata,
        FilterBuffer* input,
        FilterBuffer* output_metadata,
        FilterBuffer* output) const override;
  
    /**
     * Restore the bit size the given input into the given output.
     */
    Status run_reverse(
        const Tile& tile,
        FilterBuffer* input_metadata,
        FilterBuffer* input,
        FilterBuffer* output_metadata,
        FilterBuffer* output,
        const Config& config) const override;
  
    /** Set the max window size (in bytes) to use. */
    void set_max_window_size(uint32_t max_window_size);
  
   private:
    /** Maximum size, in bytes, of a window of input elements to compress. */
    uint32_t max_window_size_;
  
    /** Returns a new clone of this filter. */
    BitWidthReductionFilter* clone_impl() const override;
  
    /**
     * Compress a part of the filter input.
     *
     * @tparam T Tile cell datatype
     * @param input Buffer to compress
     * @param output Buffer to store compressed output.
     * @param output_metadata Buffer to store output metadata.
     * @return Status
     */
    template <typename T>
    Status compress_part(
        ConstBuffer* input,
        FilterBuffer* output,
        FilterBuffer* output_metadata) const;
  
    /**
     * Computes the number of bits required to represent elements of type T in the
     * given buffer when the element values are normalized to 0.
     *
     * @tparam T Tile cell datatype
     * @param buffer Buffer to consider
     * @param num_elements Number of elements in the window to consider from
     *    buffer
     * @param min_value Will be set to the minimum element value in the window.
     * @return Number of bits (8, 16, 32, or 64).
     */
    template <typename T>
    uint8_t compute_bits_required(
        ConstBuffer* buffer, uint32_t num_elements, T* min_value) const;
  
    /** Deserializes this filter's metadata from the given buffer. */
    Status deserialize_impl(ConstBuffer* buff) override;
  
    /** Gets an option from this filter. */
    Status get_option_impl(FilterOption option, void* value) const override;
  
    /**
     * Reads a compressed value of type T from the given buffer after
     * decompressing from a value of the given bit width.
     *
     * @tparam T Tile cell datatype
     * @param buffer Buffer to read from
     * @param compressed_bits Bit width of compressed value to read
     * @param value Will be set to the decompressed value
     * @return Status
     */
    template <typename T>
    Status read_compressed_value(
        FilterBuffer* buffer, uint8_t compressed_bits, T* value) const;
  
    /** Run_forward method templated on the tile cell datatype. */
    template <typename T>
    Status run_forward(
        const Tile& tile,
        FilterBuffer* input_metadata,
        FilterBuffer* input,
        FilterBuffer* output_metadata,
        FilterBuffer* output) const;
  
    /** Run_reverse method templated on the tile cell datatype. */
    template <typename T>
    Status run_reverse(
        const Tile& tile,
        FilterBuffer* input_metadata,
        FilterBuffer* input,
        FilterBuffer* output_metadata,
        FilterBuffer* output) const;
  
    /** Sets an option on this filter. */
    Status set_option_impl(FilterOption option, const void* value) override;
  
    /** Serializes this filter's metadata to the given buffer. */
    Status serialize_impl(Buffer* buff) const override;
  
    /**
     * Writes the given value of type T to the given buffer after compressing
     * (casting) to a value of the given bit width.
     *
     * @param buffer Buffer to write to
     * @param value Uncompressed value to write
     * @param num_bits Bit width of compressed value to write
     * @return Status
     */
    template <typename T>
    Status write_compressed_value(
        FilterBuffer* buffer, T value, uint8_t num_bits) const;
  };
  
  }  // namespace sm
  }  // namespace tiledb
  
  #endif  // TILEDB_BIT_WIDTH_REDUCTION_FILTER_H
  