void copyBlocksTo(RegularFile target, int count) {
    int start = blockCount - count;
    int targetEnd = target.blockCount + count;
    target.expandIfNecessary(targetEnd);

    System.arraycopy(this.blocks, start, target.blocks, target.blockCount, count);
    target.blockCount = targetEnd;
  }
Copies the last {@code count} blocks from this file to the end of the given target file.
jimfs/src/main/java/com/google/common/jimfs/RegularFile.java