parquet-column/src/main/java/org/apache/parquet/column/values/delta/DeltaBinaryPackingValuesReader.java
private void unpackMiniBlock(BytePackerForLong packer) throws IOException {
    for (int j = 0; j < config.miniBlockSizeInValues; j += 8) {
      unpack8Values(packer);
    }
  }
private void unpackMiniBlock(BytePackerForLong packer) throws IOException {
    for (int j = 0; j < config.miniBlockSizeInValues; j += 8) {
      unpack8Values(packer);
    }
  }
mini block has a size of 8*n, unpack 8 value each time

@param packer the packer created from bitwidth of current mini block