Method and apparatus for compressing and decompressing strings of electrical digital data bits

Claim 3

A method for compressing a binary bit string as set forth in claim 1 including a third comparison step in which a third comparison string is utilized which is the bit string to be compressed shifted by two slices so that each slice except for the first two slices, is compared with the two previous slices in the string.

Claim 4

A method for compressing a binary bit string as set forth in claim 2 further including the step of determining if an equal number of mismatches has occurred for two or more comparison strings, the one chosen depends upon the length of the associated header code.

Claim 5

A method for compressing a binary bit string as set forth in claim 3 including generating only a single flag bit and no digit bits whenever a slice to be compressed exactly matches the comparison slice and an opposite binary state flag bit whenever a mismatch occurs.

Claim 6

A digital data display system in which character cell definition bit strings are generated in a central processing unit and transmitted to a display unit including a central processing unit which includes means for compressing bit strings representing digital scan data comprising the information to be displayed said last named means comprising: means for dividing each bit string to be coded into a predetermined number of slices, each slice having a predetermined number of digits, means for comparing the bit string to be coded with a plurality of comparison strings, means for selecting as a first comparison string, a string of identical binary bits, means for selecting as a second comparison string the string to be compressed shifted by one slice and means for selecting as a third comparison string the bit string to be compressed shifted by two slices and means for comparing the bit string to be coded with each of said three comparison strings and counting and storing, for each comparison string, the number of digits in which a mismatch occurs, means for choosing as a coding base that comparison string which provided the least number of mismatches of digits, means for generating a header code for indicating which comparison string has been chosen, and means for generating a string of binary bits having a single flag bit for each successful digit comparison and a flag bit plus the full digit for each non-successful digit comparison.

Claim 7

A digital data display system in which character cell definition bit strings are generated in a central processing unit and transmitted to a display unit including a central processing unit which includes means for compressing bit strings representing digital scan data comprising the information to be displayed said last named means comprising: means for dividing each bit string to be coded into a predetermined number of slices, each slice having a predetermined number of digits, means for comparing the bit string to be coded with a plurality of comparison strings, means for selecting as a first comparison string, a string of identical binary bits, means for selecting as a second comparison string the string to be compressed shifted by one slice and means for selecting as a third comparison string the bit string to be compressed shifted by two slices and means for comparing the bit string to be coded with each of said three comparison strings and counting and storing, for each comparison string, the number of digits in which a mismatch occurs, means for choosing as a coding base that comparison string which provided the least number of mismatches of digits, means for generating a header code for indicating which comparison string has been chosen, and means for generating a string of binary bits having a single flag bit for each successful digit comparison and a flag bit plus the full digit for each non-successful digit comparison.

Claim 8

A digital display system as set forth in claim 5 including means for determining if an equal number of mismatches occurs for two or more comparison strings and means for choosing the actual comparison string based on the length of the associated header code designating that string.