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Browse Prior Art Database

Processing of Compressed Data Files

IP.com Disclosure Number: IPCOM000081336D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Tsui, F: AUTHOR

Abstract

This is an arrangement for processing compressed data files, which includes the associative scanning of records comprising front-compressed data, and the retrieval of matching records in their original noncompressed form.

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Processing of Compressed Data Files

This is an arrangement for processing compressed data files, which includes the associative scanning of records comprising front-compressed data, and the retrieval of matching records in their original noncompressed form.

In the data stream of a file read from direct access storage device 4 (Fig. 1), each record 5 consists of two control fields (Nh, Nd) and a data field. Nh indicates the number of leading data bytes which, being identical to those in the preceding record, have been omitted from the data field of the present record, whereas Nd gives the full length of the data prior to front compression. On being read out, the record 5 is entered into registers: Nh into register 6, Nd into register 7, and the data field into regeneration register 8 which is a special shift register with a variable-input point. Input control circuit 9 (Fig. 1) selects the position at which data are left-shifted into register 8 and, with the arrangement comprising decoders 10, 11 and AND gates 12 (Fig. 3) controls the number of data bytes being entered.

As shown in Figs. 2A and 2B, the leftmost position of the input range is determined by Nh via decoder 10, and the rightmost position by Nd via decoder
11. 10 and 11 are negative-level decoders, whose output on the addressed line is negative, inhibiting the AND gate 12 connected to it, whereas the outputs on the nonaddressed lines are positive, keeping their connected AND gates 12 open.

At the beginning of each record scanning operation, the new value of control field Nh, fed into register 6, is compared by comparator 19 with the content of counter 16, which...