code: func verifyCheckpoint(prevCheckpoint, nextCheckpoint *chainhash.Hash,
  	cfheaders *wire.MsgCFHeaders) bool {
  
  	if *prevCheckpoint != cfheaders.PrevFilterHeader {
  		return false
  	}
  
  	lastHeader := cfheaders.PrevFilterHeader
  	for _, hash := range cfheaders.FilterHashes {
  		lastHeader = chainhash.DoubleHashH(
  			append(hash[:], lastHeader[:]...),
  		)
  	}
  
  	return lastHeader == *nextCheckpoint
  }
docs: // verifyHeaderCheckpoint verifies that a CFHeaders message matches the passed
  // checkpoints. It assumes everything else has been checked, including filter
  // type and stop hash matches, and returns true if matching and false if not.