US 4,569,016 AGranted

Mechanism for implementing one machine cycle executable mask and rotate instructions in a primitive instruction set computing system

AssigneeInternational Business Machines Corporation

InventorsHsieh T. Hao, Peter W. Markstein, George Radin

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Abstract

A mechanism for performing fast and efficient full shift, merge, insert and bit alignment functions within one operating machine cycle of a host primitive instructions set computing system. In general, the circuitry performs a ring shift under control of a mask. The circuitry further combines essentially parallel rotate and mask and merge functions all executable in one machine cycle. The circuitry further allows the provision of powerful bit, digit, and bit rotate with mask instructions which are particularly useful primitive operations for decimal packing and unpacking functions as well as for implementing floating point preshifting and normalization functions.

Claims10

Dependent claims

In a digital electronic computing system having a single machine cycle executable instruction set and including a memory hieracrchy comprising a main memory and a high-speed cache, a Central Processing Unit (CPU) and a bus network interconnecting same, said CPU including an arithmetic and logic unit (ALU) for performing mathematical and logical operations on data supplied thereto, an instruction unit operable in cooperation with a plurality of simultaneously accessible high speed general purpose registers and said ALU for processing primitive instructions to be performed by said system, and condition code generating means for generating a plurality of specified condition bits in accordance with the output of the ALU and the instruction unit, the improvement which comprises,

a mechanism including a plurality of concurrently operable means for performing single machine cycle executable Mask and Rotate Instructions in said CPU wherein a subject operand is to be partially merged with an object operand under control of a mask, all of which are specified in one of said instructions, said mechanism comprising:
means for generating an N-bit mask word from mask edge addresses specified by mask field in the instruction,
access means for obtaining an N-bit subject operand from data specified in said instruction,
access means for obtaining one of a plurality of possible N-bit object operands from the system high speed registers from data specified in said instruction,
shifter means for rotating said N-bit subject operand which is to be merged with an N-bit object operand by an amount specified in said instruction,
combinatorial circuit means for merging said rotated subject operand into said object operand under control of said mask so that data representative of the object operand is retained where said mask has a first binary content and data representative of the rotated subject operand is retained where said mask has the opposite binary content, and
means for returning said retained merged N-bit word to a register in the CPU specified by said instructions.

4 more elements

A method for use in a program controlled digital electronic computing system for performing a powerful class of Mask and Rotate instructions capable of performing a wide variety of data shifting functions, said functions including inserting a portion of a subject operand under control of an N-bit mask into a variety of different types of N-bit object operands, said method including the steps of

accessing from the instruction an address in the system's local high speed storage registers of the subject operand, a portion of which is to be inserted into said object operand, generating said N-bit mask from a `mask` filed in the instruction, which Mask defines the field of the subject operand to be inserted and also the specific field within the object operand where the subject operand is to be inserted,
realigning the N-bit subject operand within its own N-bit space an amount necessary to align a particular field thereof with the filed of the object operand into which said subject field is to be inserted, and
accessing the particular object operand specified by said instruction into which said subject operand is to be inserted.

Dependencies are inferred from the claim text.