Function DoSplitStreams

cpp/src/arrow/util/byte_stream_split_internal.h:325–364

//

inline void DoSplitStreams(const uint8_t* src, int width, int64_t nvalues,
                           uint8_t** dest_streams) {
  // Value empirically chosen to provide the best performance on the author's machine
  constexpr int kBlockSize = 32;

  while (nvalues >= kBlockSize) {
    for (int stream = 0; stream < width; ++stream) {
      uint8_t* dest = dest_streams[stream];
      for (int i = 0; i < kBlockSize; i += 8) {
        uint64_t a = src[stream + i * width];
        uint64_t b = src[stream + (i + 1) * width];
        uint64_t c = src[stream + (i + 2) * width];
        uint64_t d = src[stream + (i + 3) * width];
        uint64_t e = src[stream + (i + 4) * width];
        uint64_t f = src[stream + (i + 5) * width];
        uint64_t g = src[stream + (i + 6) * width];
        uint64_t h = src[stream + (i + 7) * width];
#if ARROW_LITTLE_ENDIAN
        uint64_t r = a | (b << 8) | (c << 16) | (d << 24) | (e << 32) | (f << 40) |
                     (g << 48) | (h << 56);
#else
        uint64_t r = (a << 56) | (b << 48) | (c << 40) | (d << 32) | (e << 24) |
                     (f << 16) | (g << 8) | h;
#endif
        arrow::util::SafeStore(&dest[i], r);
      }
      dest_streams[stream] += kBlockSize;
    }
    src += width * kBlockSize;
    nvalues -= kBlockSize;
  }

  // Epilog
  for (int stream = 0; stream < width; ++stream) {
    uint8_t* dest = dest_streams[stream];
    for (int64_t i = 0; i < nvalues; ++i) {
      dest[i] = src[stream + i * width];
    }
  }
}

inline void DoMergeStreams(const uint8_t** src_streams, int width, int64_t nvalues,
                           uint8_t* dest) {