Method GetBatch

cpp/src/arrow/util/rle_bitmap_internal.h:122–149

Get a batch of values into `out` and return the number of decoded elements. May write fewer elements to the output than requested if there are not enough values left.

  /// May write fewer elements to the output than requested if there are not
  /// enough values left.
  [[nodiscard]] rle_size_t GetBatch(BitmapSpanMut out, rle_size_t batch_size) {
    const auto out_bit_offset = out.bit_start();
    ARROW_DCHECK_GE(out_bit_offset, 0);
    ARROW_DCHECK_LT(out_bit_offset, 8);

    if (ARROW_PREDICT_FALSE(remaining() == 0 || batch_size == 0)) {
      return 0;
    }

    rle_size_t n_vals = 0;

    // HEADER: Writing inside the first byte if caller gives a non-aligned input
    if (out_bit_offset != 0) {
      n_vals = GetBatchInByte(out, batch_size);
    }

    // Writing full bytes
    n_vals += GetBatchFullBytes(out.NewStartingAt(n_vals), batch_size - n_vals);

    // TRAILER: Writing inside the last byte if caller asked for non multiple of 8 values
    const auto n_last_vals = std::min(batch_size - n_vals, remaining());
    if (n_last_vals > 0) {
      ARROW_DCHECK_LT(n_last_vals, 8);
      n_vals += GetBatchInByte(out.NewStartingAt(n_vals), n_last_vals);
    }

    return n_vals;
  }

 private:
  /// The byte pattern for 8 values (full ones or full zeros).