Browse Prior Art Database

Data Length Calculation Hardware

IP.com Disclosure Number: IPCOM000085794D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Plant, JW: AUTHOR [+2]

Abstract

Hardware is provided in a digital computer or digital data processor for subtracting the two register designation fields in load multiple and store multiple type machine instructions, for obtaining a very quick determination of the number of bytes of data to be loaded or stored.

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Data Length Calculation Hardware

Hardware is provided in a digital computer or digital data processor for subtracting the two register designation fields in load multiple and store multiple type machine instructions, for obtaining a very quick determination of the number of bytes of data to be loaded or stored.

For the machine instructions load multiple (LM), store multiple (STM), load control registers (LCTL) and store control registers (STCTL), the number of four- byte general purpose registers whose data is to be transferred is given by bits 8- 15 of the machine instruction. Bits 8-11 indicate the starting register (R1) and bits 12-15 indicate the ending register (R3).

If the two fields are equal (starting register equal ending register), then only the contents of that register are transferred. If the ending register has a lower designation number than the starting register, then the contents of those registers counting from the starting register (R1) through the highest numbered register (F) plus those registers counting from the lowest numbered register (0) through the ending register (R3) are transferred.

In existing microprogrammed data processors, a series of microcode steps is required to operate on these types of instructions to determine the amount of data to be transferred. The hardware described herein eliminates these microcode steps and determines the amount of data automatically, thereby reducing the overall execution time for instructions of this type.

As indicated in the drawing, the data length is calculated very quickly and very efficiently by utilizing a read-only storage (ROS) device 10 to perform a table look-up func...