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Table Look Up

IP.com Disclosure Number: IPCOM000076615D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 31K

Publishing Venue

IBM

Related People

Mascarenhas, J: AUTHOR

Abstract

This assembler module for PL/1 has a plurality of entry points (INIT, REC1 . . . RECn) and performs a dichotomizing search of declared tables, using the two pointers associated with each of the items that make up such tables. The main advantage of this module being that it is very fast.

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Table Look Up

This assembler module for PL/1 has a plurality of entry points (INIT, REC1 .
. . RECn) and performs a dichotomizing search of declared tables, using the two pointers associated with each of the items that make up such tables. The main advantage of this module being that it is very fast.

A table consists of a series of items having an identical structure, each item comprising an argument and one or more functions. The items are sorted according to the value of the arguments, beginning with the lower values.

To find any item in the table, knowing the search argument, successive comparisons are made between the search argument and the arguments associated with various items until a match is found.

The search may be performed sequentially by comparing the search argument with the argument associated with each item in the table, beginning with the first item.

This method, while very simple takes too much time. The dichotomizing search, on the other hand, first looks up an item located in the middle of the table, then the item located in the middle of one of the two halves of the table, and so on. The match is thus found far more quickly.

However, this implies that, before each test, the address of the next successive item to be looked-up must be calculated. The present method eliminates the need for such calculations and saves a considerable amount of time as compared with a conventional dichotomizing search. Summary Each item in the table consists of three positions: - two pointers (PINF and PSUP) - an argument - one or more functions.

For each item, pointer PINF contains the address of the next item to be examined, if the value of the search argument is lower than that of the argument with which it has just been compared. Pointer PSUP contains the address of the next item to be examined, if the value of the search argument is higher than that of the argument with which it has just been compared.

The pointers are automati...