Hewlett-packard Company

Michael J Mahon

William R Bryg

Ruby B Lee

Allen Jay Baum

Terrence C Miller

David V James

Dale Calvin Morris

Jerome C Huck

Stephen G Burger

William S Worley, Jr

Daryl K Odnert

Steven C Boettner

Steven S Muchnick

Vivek S Pendharkar

Tso-Kai Liu

Circuitry combines a first operand A.sub.0, a second operand A.sub.1, and a third operand X in a blend function to produce a result Z. The result Z has a value equal to X*A.sub.0 +(1-X)* A.sub.1. The circuitry includes a plurality of logic gates organized in rows. When performing the blend operation each logic gates selects either a bit of the first operand A.sub.0 or a bit of the second operand A.sub.1. The selection for each logic gate depends upon bits of the third operand X. More specifically, each of the plurality of rows of logic gates selects the first operand A.sub.0 as output when an associated bit of the third operand X is at logic 1, and selects the second operand A.sub.1 as output when the associated bit of the third operand X is at logic 0. In addition to output generated by the plurality of rows of logic gates, a correction term is generated. For the blend operation, the correction term generated is the second operand A.sub.1. Partial product circuitry sums outputs of each row of logic gates and the correction term, to produce the result Z, so that the result Z has a value equal to X*A.sub.0 +(1-X)*A.sub.1.

Expediting blending and interpolation via multiplication

A method for operating a digital computer in response to the occurrence of an exception is disclosed. The method provides for the examination both of the contents of a predetermined computer location and of the instruction code for the instruction causing the exception. The computer then utilizes the result of those examinations to determine the dismissibility of the exception. The computer transfers control to the next instruction after the instruction which caused the exception if that instruction is dismissible.

Software method for implementing dismissible instructions on a computer

In a computing system a method for performing a multiplication of a first multiplicand and a second multiplicand is presented. The computing system includes a plurality of registers, an instruction decoder, an arithmetic logic unit, and a preshifter. The first multiplicand is divided into a plurality of equal length sections. Each section includes 'n' bits, where 'n' is an integer greater than one. The second multiplicand is placed in a first register from the plurality of registers. A second register from the plurality of registers is cleared to zero. For each section from the plurality of sections, starting with a first section containing high order bits of the first multiplication and proceeding to a last section of the first multiplicand containing low order bits of the first multiplicand the following three substeps. First, when the low order bit of a current section is a '1', the contents of the first register are added to the contents of the second register via the arithmetic logic unit. Second, for every other bit in the current section that is a '1', a shift-and-add operation is performed by shifting, via the preshifter, the contents of the first register by an amount equal to the number of bit places the bit is to the left of the low order bit of the current section and by adding, via the arithmetic logic unit, the preshifted contents of the first register to the contents of the second register. Third, for every section from the plurality of sections that does not contain low order bits of the first multiplicand, the contents of the first register 'n' bits are shifted to the left.

Method in a computing system for performing a multiplication

An instruction is presented to the cache; the instruction includes a cache control specifier which identifies a type of data being requested. Based on the cache control specifier, one of a plurality of replacement schemes is selected for swapping a data block out of the cache.

Cache memory with variable fetch and replacement schemes

A low overhead way for insuring that only routines of sufficient privilege can execute on a secured page of memory in an hierarchial computer system, and for raising the privilege level of a low privilege process in an orderly and secure way is presented. This is done through the execution of a single 'gateway' branch instruction standing between a procedure call by a lower privileged routine, such as a user program, and an operating system itself.

Privilege level checking instruction for implementing a secure

A virtual memory system is used to control access to I/O device address space in accordance with a preferred embodiment of the present invention. In a virtual memory system, access to pages within a processor's address space are assigned to each application program. Each I/O device is assigned two pages of address space. One page is considered to be privileged, and the other unprivileged. Each I/O device register is associated with an address in each of the two pages of its I/O device address space. Address space is global. What is meant by global is that physical memory locations map to the same virtual memory space regardless of what process is running on the processor. Access codes accompanied by a write disable bit are used to control process access to various addresses.

Direct input/output in a virtual memory system

A computer and an instruction set are presented which allow for a number of assists to be easily incorporated into the computer, and which allow for an instruction set extension. The computer is designed to support instructions which move data between an assist and a location, although an assist's operation and design need not be defined at the computer's date of design. Instructions are mapped to a particular assist. Assist instructions can be either executed in hardware by an assist, or emulated in software via a trap.

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San Jose, CA, United States of America

Michael J Mahon