Browse Prior Art Database

Rapid Scanning for Null and Attribute Characters

IP.com Disclosure Number: IPCOM000088148D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 97K

Publishing Venue

IBM

Related People

Winn, GC: AUTHOR

Abstract

Fig. 1 illustrates a visual display system including display screen 1, display controls 2 including a display buffer, and controlling processor 3. Information appears on screen 1 as a matrix of characters of m columns by n rows. Characters which are displayed are stored in character buffer 4 within processor 3 as a contiguous list of m x n eight-bit character codes. A cursor, displayed on screen 1 as an underscore, acts as a pointer to one of the m x n buffer locations.

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Rapid Scanning for Null and Attribute Characters

Fig. 1 illustrates a visual display system including display screen 1, display controls 2 including a display buffer, and controlling processor 3. Information appears on screen 1 as a matrix of characters of m columns by n rows. Characters which are displayed are stored in character buffer 4 within processor 3 as a contiguous list of m x n eight-bit character codes. A cursor, displayed on screen 1 as an underscore, acts as a pointer to one of the m x n buffer locations.

Normal alphanumeric characters are allocated codes in the range 00000000 to 01111111: thus bit 0 is always 0. Included within this range are nulls
(00000000). Attribute characters are allocated codes in the range 10000000 to 10111111: thus bit 0 is always 1.

Nulls appear on display screen 1 as a blank, but are distinct from spaces which have a different alphanumeric character code; they are of interest when character insertions occur. Character insertions cause all adjacent alphanumeric characters to the right of the insert position as far as the first null to be displaced one place to the right, causing the null to be overwritten. The displaced characters will wrap from one line to the next and from the end to the start of the buffer, where appropriate. If there are no nulls in the field to the right of the insert position, then character insertions are not permitted to take place. Attribute characters also appear on display screen 1 as a blank and are used to define the start of a new field and to store the attributes of that field (displayable, unprotected, numeric, etc.).

It is a frequent requirement within controlling processor 3 to scan through the character buffer from the cursor or some other position, forwards or backwards, searching for nulls or attribute characters. For example, it is often necessary to locate the attribute character of a given field to determine the attributes of that field or to reposition the cursor to the start of the previous, current, or next unprotected field. Similarly, it is necessary to search for nulls when determining whether or not an ins...