A computer implemented method of performing data compression includes applying, with a computing device, a hash function to a selected part of a character string to calculate a hash value; searching, using the hash value, through entries in a bucket chain having the hash value previously registered in a hash table, and finding a longest matching character string; acquiring, an index indicating that a longest matching character string cannot be found in the search through the entries and thus the search operation is wasted; and switching the hash function to a different hash function for expanding the selected part of the character string, without reconstructing the hash table, when the index exceeds a predetermined threshold.