Browse Prior Art Database

End of List Indicator Mechanism

IP.com Disclosure Number: IPCOM000088413D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Wingert, JA: AUTHOR

Abstract

An end-of-list indicator bit is included with each list entry for eliminating a testing step in a list searching loop.

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End of List Indicator Mechanism

An end-of-list indicator bit is included with each list entry for eliminating a testing step in a list searching loop.

A digital data processor in which the data flow uses a register to temporarily latch data being transferred between main storage and local storage can provide a useful microprogramming enhancement. The high-order bit of the data being transferred can be assigned an indicator function and can be examined by the read data microword while the data is temporarily latched in the register. The value of this high-order bit can be used in the selection of the next microword to be executed.

A list structure can be defined which utilizes this capability by defining the high-order bit of each list entry as an end-of-list indicator bit. The end-of-list checking can then be performed simultaneously with the reading of the list entries from storage.

The flow chart of Fig. 1 shows the normal prior art list searching technique. The flow chart of Fig. 2 shows the improvement made possible by the use of the end-of-list indicator bit. Such use eliminates the end-of-list checking or testing step in the list searching loop and, therefore, improves performance. The end-of- list bit is examined while the list entry is temporarily latched in the data flow register, and its value automatically selects the next step to be executed.

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