| 摘要 |
When input data composed of a symbol string is compressed, bit maps are used. In each bit map, "1" is set to a bit that represents the position of a relevant symbol of the symbol string. In contrast, "0" is set to a bit that represents the position of another symbol of the symbol string. When compressed data is expanded, symbols are expanded in the order thereof. Thus, the positions of symbols that have been expanded are omitted from each bit map. Consequently, each bit map can be shortened and thereby the compression ratio can be improved. Since the length of each bit map is variable, a value of which (the number of symbols expanded by corresponding bit map-2) is added as information for expanding symbols from each variable bit map of the compressed data correctly. In addition, to distinguish data having a bit map from data having no bit map, a flag that represents the presence of a bit map is added to the compressed data.
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