code: public static byte[] decompressFast(byte[] src, int srcOffset, int exactDecompressedSize) {
          if (src == null) {
              throw new IllegalArgumentException("src must not be null.");
          }
  
          if (srcOffset < 0) {
              throw new IllegalArgumentException("srcOffset must equal to or larger than 0 but " + srcOffset);
          }
  
          if (exactDecompressedSize < 0) {
              throw new IllegalArgumentException("exactDecompressedSize must equal to or larger than 0 but " + exactDecompressedSize);
          }
  
          LZ4FastDecompressor decompressor = factory.fastDecompressor();
  
          return decompressor.decompress(src, srcOffset, exactDecompressedSize);
      }
docs: When the exact decompressed size is known, use this method to decompress. It's faster.
  
  @see net.jpountz.lz4.LZ4FastDecompressor