Browse Prior Art Database

Partial Byte Computations

IP.com Disclosure Number: IPCOM000082444D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Gooding, DN: AUTHOR [+2]

Abstract

This technique enables arithmetic computations to be performed on numerical data items having boundaries which do not fall on byte boundaries.

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Partial Byte Computations

This technique enables arithmetic computations to be performed on numerical data items having boundaries which do not fall on byte boundaries.

Fig. 1 shows an example of the type of data format being considered and Fig. 2 shows apparatus for performing arithmetic computations on such data. In this example, it is assumed that each unit in the arithmetic apparatus has a width of two bytes (sixteen bits) and that the data entering each unit is also two bytes (sixteen bits) in width.

As indicated in Fig. 1, each two-byte data item contains two groups of data with the Group 1 data occupying the more significant bit positions. The eleven bits in Group 1 represent a first numerical.quantity, while the five bits in Group 2 represent a second numerical quantity or some other type of data. The boundary between Groups 1 and 2 does not coincide with a byte boundary. The object is to add or subtract the Group 1 portion of a first data item A from the Group 1 portion of a second data item B.

The problem is to prevent any bit carry generated by the Group 2 portions from being carried over into the computations for the Group 1 portions. A further complication is that provision should be made for enabling the Group 1 computation to receive an external carry-in from a previous operation or other source. The solution is to force the bits in the Group 2 portion of one data item to G and the bits in the Group 2 portion of the other data item to 1 before the data items are supplied to the adder.

Apparatus for ac...