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Densely Packed Decimal (DPD) is a system of binary encoding fordecimal digits. The traditional system of binary encoding for decimal digits, known as Binary-coded decimal (BCD), uses four bits to encode each digit, resulting in significant wastage of binary data bandwidth (since four bits can store 16 states and are being used to store only 10). In 1971, Tien Chi Chen and Dr. Irving T. Ho devised a lossless code (now known as Chen-Ho encoding) which used Huffman coding to pack three digits into 10 bits using a scheme which allowed compression from or expansion to BCD with only two or three gate delays in hardware. Densely Packed Decimal is an encoding which gives the same compression and speed advantages, but is not a prefix code; the particular arrangement of bits used confers further advantages:
Examples This table shows some representative decimal numbers and their encodings in BCD, Chen-Ho, and Densely Packed Decimal (DPD): | ||||||||
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