# Patent

## Title
Methods and apparatus for efficient complex long multiplication and covariance matrix implementation

## Abstract

Efficient computation of complex long multiplication results and an efficient calculation of a covariance matrix are described. A parallel array VLIW digital signal processor is employed along with specialized complex long multiplication instructions and communication operations between the processing elements which are overlapped with computation to provide very high performance operation. Successive iterations of a loop of tightly packed VLIWs may be used allowing the complex multiplication pipeline hardware to be efficiently used.

## Background
RELATED APPLICATIONS
The present application is a continuation of U.S. Ser. No. 11/438,418 filed May 22, 2006, now U.S. Pat. No. 7,680,873, which is a continuation of U.S. Ser. No. 10/004,010 filed Nov. 1, 2001, now U.S. Pat. No. 7,072,929 and claims the benefit of U.S. Provisional Application Ser. No. 60/244,861 filed Nov. 1, 2000, which are incorporated by reference herein in their entirety.


FIELD OF THE INVENTION
The present invention relates generally to improvements to parallel processing, and more particularly to methods and apparatus for efficiently calculating the result of a long complex multiplication. Additionally, the present invention relates to the advantageous use of this approach for the calculation of a covariance matrix.
BACKGROUND OF THE INVENTION
The product of two complex numbers x and y is defined to be z=xRyR−x1y1+i(xRy1+x1yR), where x=xR+ix1, y=yR+iy1 and i is an imaginary number, or the square root of negative one, with i2=−1. This complex multiplication of x and y is calculated in a variety of contexts, and it has been recognized that it will be highly advantageous to perform this calculation faster and more efficiently.
SUMMARY OF THE INVENTION
The present invention defines hardware instructions to calculate the product of two complex numbers encoded as a pair of two fixed-point numbers of 16 bits each. The product may be calculated in two cycles with single cycle pipeline throughput efficiency, or in a single cycle. The product is encoded as a 32 bit real component and a 32 bit imaginary component. The present invention also defines a series of multiply complex instructions with an accumulate operation. Additionally, the present invention also defines a series of multiply complex instructions with an extended precision accumulate operation. The complex long instructions and methods of the present invention may be advantageously used in a variety of contexts, including calculation of a fast Fourier transform as addressed in U.S. patent application Ser. No. 09/337,839 filed Jun. 22, 1999 entitled “Efficient Complex Multiplication and Fast Fourier Transform (FFT) Implementation on the ManArray Architecture” which is incorporated by reference herein in its entirety. The multiply complex instructions of the present invention may be advantageously used in the computation of a covariance matrix, as described below.
A more complete understanding of the present invention, as well as other features and advantages of the invention will be apparent from the following Detailed Description and the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an exemplary 2×2 ManArray iVLIW processor;
FIG. 2A illustrates a multiply complex long (MPYCXL) instruction in accordance with the present invention;
FIGS. 2B and 2C illustrate the syntax and operation of the MPYCXL instruction of FIG. 2A;
FIG. 3A illustrates a multiply complex conjugate long (MPYCXJL) instruction in accordance with the present invention;
FIGS. 3B and 3C illustrate the syntax and operation of the MPYCXJL instruction of FIG. 3A;
FIG. 4A illustrates a multiply complex long accumulate (MPYCXLA) instruction in accordance with the present invention;
FIGS. 4B and 4C illustrate the syntax and operation of the MPYCXLA instruction of FIG. 4A;
FIG. 5A illustrates a multiply complex conjugate long accumulate (MPYCXJLA) instruction in accordance with the present invention;
FIGS. 5B and 5C illustrate the syntax and operation of the MPYCXJLA instruction of FIG. 5A;
FIG. 6A illustrates a multiply complex long extended precision accumulate (MPYCXLXA) instruction in accordance with the present invention;
FIGS. 6B and 6C illustrate the syntax and operation of the MPYCXLXA instruction of FIG. 6A;
FIG. 7A illustrates a multiply complex conjugate long extended precision accumulate (MPYCXJLXA) instruction in accordance with the present invention;
FIGS. 7B and 7C illustrates the syntax and operation of the MPYCXJLXA instruction of FIG. 7A;
FIG. 8 shows a block diagram illustrating various aspects of hardware suitable for performing the MPYCXL, MPYCXJL, MPYCXLA, MPYCXJLA, MPYCXJLA, MPYCXLXA and MPYCXJLXA instructions in two cycles of operation in accordance with the present invention;
FIG. 9 shows an integrated product adder and accumulator in accordance with the present invention;
FIG. 10 shows a block diagram illustrating various aspects of hardware suitable for performing the MPYCXL, MPYCXJL, MPYCXLA, MPYCXJLA, MPYCXJLA, MPYCXLXA and MPYCXJLXA instructions in a single cycle of operation in accordance with the present invention; and
FIGS. 11A-11I illustrate the calculation of a covariance matrix on a 2×2 processing array in accordance with the present invention.



DETAILED DESCRIPTION
Further details of a presently preferred ManArray core, architecture, and instructions for use in conjunction with the present invention are found in: U.S. patent application Ser. No. 08/885,310 filed Jun. 30, 1997, now U.S. Pat. No. 6,023,753, U.S. patent application Ser. No. 08/949,122 filed Oct. 10, 1997, now U.S. Pat. No. 6,167,502, U.S. patent application Ser. No. 09/169,256 filed Oct. 9, 1998, now U.S. Pat. No. 6,167,501, U.S. patent application Ser. No. 09/169,072 filed Oct. 9, 1998, now U.S. Pat. No. 6,219,776, U.S. patent application Ser. No. 09/187,539 filed Nov. 6, 1998, now U.S. Pat. No. 6,151,668, U.S. patent application Ser. No. 09/205,558 filed Dec. 4, 1998, now U.S. Pat. No. 6,173,389, U.S. patent application Ser. No. 09/215,081 filed Dec. 18, 1998, now U.S. Pat. No. 6,101,592, U.S. patent application Ser. No. 09/228,374 filed Jan. 12, 1999, now U.S. Pat. No. 6,216,223, U.S. patent application Ser. No. 09/471,217 filed Dec. 23, 1999, now U.S. Pat. No. 6,260,082, U.S. patent application Ser. No. 09/472,372 filed Dec. 23, 1999, now U.S. Pat. No. 6,256,683, U.S. patent application Ser. No. 09/238,446 filed Jan. 28, 1999, U.S. patent application Ser. No. 09/267,570 filed Mar. 12, 1999, U.S. patent application Ser. No. 09/337,839 filed Jun. 22, 1999, U.S. patent application Ser. No. 09/350,191 filed Jul. 9, 1999, U.S. patent application Ser. No. 09/422,015 filed Oct. 21, 1999, U.S. patent application Ser. No. 09/432,705 filed Nov. 2, 1999, U.S. patent application Ser. No. 09/596,103 filed Jun. 16, 2000, U.S. patent application Ser. No. 09/598,567 filed Jun. 21, 2000, U.S. patent application Ser. No. 09/598,564 filed Jun. 21, 2000, U.S. patent application Ser. No. 09/598,566 filed Jun. 21, 2000, U.S. patent application Ser. No. 09/598,558 filed Jun. 21, 2000, U.S. patent application Ser. No. 09/598,084 filed Jun. 21, 2000, U.S. patent application Ser. No. 09/599,980 filed Jun. 22, 2000, U.S. patent application Ser. No. 09/711,218 filed Nov. 9, 2000, U.S. patent application Ser. No. 09/747,056 filed Dec. 12, 2000, U.S. patent application Ser. No. 09/853,989 filed May 11, 2001, U.S. patent application Ser. No. 09/886,855 filed Jun. 21, 2001, U.S. patent application Ser. No. 09/791,940 filed Feb. 23, 2001, U.S. patent application Ser. No. 09/792,819 filed Feb. 23, 2001, U.S. patent application Ser. No. 09/791,256 filed Feb. 23, 2001, U.S. patent application Ser. No. 10/013,908 entitled “Methods and Apparatus for Efficient Vocoder Implementations” filed Oct. 19, 2001, Provisional Application Ser. No. 60/251,072 filed Dec. 4, 2000, Provisional Application Ser. No. 60/281,523 filed Apr. 4, 2001, Provisional Application Ser. No. 60/283,582 filed Apr. 13, 2001, Provisional Application Ser. No. 60/287,270 filed Apr. 27, 2001, Provisional Application Ser. No. 60/288,965 filed May 4, 2001, Provisional Application Ser. No. 60/298,624 filed Jun. 15, 2001, Provisional Application Ser. No. 60/298,695 filed Jun. 15, 2001, Provisional Application Ser. No. 60/298,696 filed Jun. 15, 2001, Provisional Application Ser. No. 60/318,745 filed Sep. 11, 2001, Provisional Application Ser. No. 60/340,620 entitled “Methods and Apparatus for Video Coding” filed Oct. 30, 2001, Provisional Application Ser. No. 60/335,159 entitled “Methods and Apparatus for a Bit Rate Instruction” filed Nov. 1, 2001, all of which are assigned to the assignee of the present invention and incorporated by reference herein in their entirety.
In a presently preferred embodiment of the present invention, a ManArray 2×2 iVLIW single instruction multiple data stream (SIMD) processor 100 shown in FIG. 1 contains a controller sequence processor (SP) combined with processing element-0 (PE0) SP/PE0 101, as described in further detail in U.S. application Ser. No. 09/169,072 entitled “Methods and Apparatus for Dynamically Merging an Array Controller with an Array Processing Element”. Three additional PEs 151, 153, and 155 are also utilized. It is noted that the PEs can be also labeled with their matrix positions as shown in parentheses for PE0 (PE00) 101, PE1 (PE01) 151, PE2 (PE10) 153, and PE3 (PE11) 155.
The SP/PE0 101 contains a fetch controller 103 to allow the fetching of short instruction words (SIWs) from a 32-bit instruction memory 105. The fetch controller 103 provides the typical functions needed in a programmable processor such as a program counter (PC), branch capability, digital signal processing, EP loop operations, support for interrupts, and also provides the instruction memory management control which could include an instruction cache if needed by an application. In addition, the SIW I-Fetch controller 103 dispatches 32-bit SIWs to the other PEs in the system by means of a 32-bit instruction bus 102.
In this exemplary system, common elements are used throughout to simplify the explanation, though actual implementations are not so limited. For example, the execution units 131 in the combined SP/PE0 101 can be separated into a set of execution units optimized for the control function, e.g. fixed point execution units, and the PE0 as well as the other PEs 151, 153 and 155 can be optimized for a floating point application. For the purposes of this description, it is assumed that the execution units 131 are of the same type in the SP/PE0 and the other PEs. In a similar manner, SP/PE0 and the other PEs use a five instruction slot iVLIW architecture which contains a very long instruction word memory (VIM) memory 109 and an instruction decode and VIM controller function unit 107 which receives instructions as dispatched from the SP/PE0's I-Fetch unit 103 and generates the VIM addresses-and-control signals 108 required to access the iVLIWs stored in the VIM. These iVLIWs are identified by the letters SLAMD in VIM 109. The loading of the iVLIWs is described in further detail in U.S. patent application Ser. No. 09/187,539 entitled “Methods and Apparatus for Efficient Synchronous MIMD Operations with iVLIW PE-to-PE Communication”. Also contained in the SP/PE0 and the other PEs is a common PE configurable register file 127 which is described in further detail in U.S. patent application Ser. No. 09/169,255 entitled “Methods and Apparatus for Dynamic Instruction Controlled Reconfiguration Register File with Extended Precision”.
Due to the combined nature of the SP/PE0, the data memory interface controller 125 must handle the data processing needs of both the SP controller, with SP data in memory 121, and PE0, with PE0 data in memory 123. The SP/PE0 controller 125 also is the source of the data that is sent over the 32-bit broadcast data bus 126. The other PEs 151, 153, and 155 contain common physical data memory units 123′, 123′′, and 123′′′ though the data stored in them is generally different as required by the local processing done on each PE. The interface to these PE data memories is also a common design in PEs 1, 2, and 3 and indicated by PE local memory and data bus interface logic 157, 157′ and 157′′. Interconnecting the PEs for data transfer communications is the cluster switch 171 more completely described in U.S. patent application Ser. No. 08/885,310 entitled “Manifold Array Processor”, U.S. application Ser. No. 09/949,122 entitled “Methods and Apparatus for Manifold Array Processing”, and U.S. application Ser. No. 09/169,256 entitled “Methods and Apparatus for ManArray PE-to-PE Switch Control”. The interface to a host processor, other peripheral devices, and/or external memory can be done in many ways. The primary mechanism shown for completeness is contained in a direct memory access (DMA) control unit 181 that provides a scalable ManArray data bus 183 that connects to devices and interface units external to the ManArray core. The DMA control unit 181 provides the data flow and bus arbitration mechanisms needed for these external devices to interface to the ManArray core memories via the multiplexed bus interface represented by line 185. A high level view of a ManArray Control Bus (MCB) 191 is also shown.
All of the above noted patents are assigned to the assignee of the present invention and incorporated herein by reference in their entirety.
Turning now to specific details of the ManArray processor as adapted by the present invention, the present invention defines the following special hardware instructions that execute in each multiply accumulate unit (MAU), one of the execution units 131 of FIG. 1 and in each PE, to handle the multiplication of complex numbers.
FIG. 2A shows a multiply complex long (MPYCXL) instruction 200 for the multiplication of two complex numbers in accordance with the present invention. The syntax and operation description 210 of the MPYCXL instruction 200 are shown in FIGS. 2B and 2C. As seen in diagram 220 of FIG. 2C, the MPYCXL instruction 200 provides for the multiplication of two complex numbers stored in source register Rx and source register Ry. In step 222, the complex numbers to be multiplied are organized in the source registers such that H1 contains the real component of the complex numbers and H0 contains the imaginary component of the complex numbers. In step 224, the complex numbers are multiplied to produce the products Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi. Next, in step 226, the products are subtracted and added in the form of (Xr*Yr)−(Xi*Yi) and (Xr*Yi)+(Xi*Yr). In step 228, the final result is written back to the target registers at the end of an operation cycle of the MPYCXL instruction 200 with a 32-bit real component and a 32-bit imaginary component placed in the target registers such that Rto contains the 32-bit real component and Rte contains the 32-bit imaginary component.
FIG. 3A shows a multiply complex conjugate long (MPYCXJL) instruction 300 for the multiplication of a first complex number and the conjugate of a second complex number in accordance with the present invention. The syntax and operation description 310 of the MPYCXJL instruction 300 are shown in FIGS. 3B and 3C. As seen in diagram 320 of FIG. 3C, the MPYCXJL instruction 300 provides for the multiplication of two complex numbers stored in source register Rx and source register Ry. In step 322, the complex numbers to be multiplied are organized in the source registers such that H1 contains the real component of the complex numbers and H0 contains the imaginary component of the complex numbers. In step 324, the complex numbers are multiplied to produce the products Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi. Next, in step 326, the products are subtracted and added in the form of (Xr*Yr)+(Xi*Yi) and (Xi*Yr)−(Xr*Yi). In step 328, the final result is written back to the target registers at the end of an operation cycle of the MPYCXJL instruction 300 with a 32-bit real component and a 32-bit imaginary component placed in the target registers such that Rto contains the 32-bit real component and Rte contains the 32-bit imaginary component.
FIG. 4A shows a multiply complex long accumulate (MPYCXLA) instruction 400 for the multiplication of two complex numbers to form a product which is accumulated with the contents of target registers in accordance with the present invention. The syntax and operation description 410 of the MPYCXLA instruction 400 are shown in FIGS. 4B and 4C. As seen in diagram 420 of FIG. 4C, the MPYCXLA instruction 400 provides for the multiplication of two complex numbers stored in source register Rx and source register Ry. In step 422, the complex numbers to be multiplied are organized in the source registers such that H1 contains the real component of the complex numbers and H0 contains the imaginary component of the complex numbers. In step 424, the complex numbers are multiplied to produce the products Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi. Next, in step 426, the products are subtracted and added in the form of (Xr*Yr)−(Xi*Yi) and (Xr*Yi)+(Xi*Yr). In step 428, (Xr*Yr)−(Xi*Yi) is added to the contents of target register Rto and (Xr*Yi)+(Xi*Yr) is added, or accumulated, to the contents of target register Rte. The final result is written back to the target registers at the end of an operation cycle of the MPYCXLA instruction 400 with a 32-bit real component and a 32-bit imaginary component placed in the target registers such that Rto contains the 32-bit real component and Rte contains the 32-bit imaginary component. For a two cycle embodiment, the target registers are fetched on a second cycle of execution to allow repetitive pipelining to a single accumulation register even-odd pair.
FIG. 5A shows a multiply complex conjugate long accumulate (MPYCXJLA) instruction 500 for the multiplication of a first complex number and the conjugate of a second complex number to form a product which is accumulated with the contents of target registers in accordance with the present invention. The syntax and operation description 510 of the MPYCXJLA instruction 500 are shown in FIGS. 5B and 5C. As seen in diagram 520 of FIG. 5C, the MPYCXJLA instruction 500 provides for the multiplication of two complex numbers stored in source register Rx and source register Ry. In step 522, the complex numbers to be multiplied are organized in the source registers such that H1 contains the real component of the complex numbers and H0 contains the imaginary component of the complex numbers. In step 524, the complex numbers are multiplied to produce the products Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi. Next, in step 526, the products are added and subtracted in the form of (Xr*Yr)+(Xi*Yi) and (Xi*Yr)−(Xr*Yi). In step 528, (Xr*Yr)+(Xi*Yi) is added, or accumulated, to the contents of target register Rto and (Xi*Yr)−(Xr*Yi) is added to the contents of target register Rte. The final result is written back to the target registers at the end of an operation cycle of the MPYCXJLA instruction 500 with a 32-bit real component and a 32-bit imaginary component placed in the target registers such that Rto contains the 32-bit real component and Rte contains the 32-bit imaginary component. For a two cycle embodiment, the target registers are fetched on the second cycle of execution to allow repetitive pipelining to a single accumulation register even-odd pair.
FIG. 6A shows a multiply complex long extended precision accumulate (MPYCXLXA) instruction 600 for the multiplication of two complex numbers to form a product which is accumulated with the contents of the extended precision target registers in accordance with the present invention. The syntax and operation description 610 of the MPYCXLXA instruction 600 are shown in FIGS. 6B and 6C. As seen in diagram 620 of FIG. 6C, the MPYCXLXA instruction 600 provides for the multiplication of two complex numbers stored in source register Rx and source register Ry. In step 622, the complex numbers to be multiplied are organized in the source registers such that H1 contains the real component of the complex numbers and H0 contains the imaginary component of the complex numbers. In step 624, the complex numbers are multiplied to produce the products Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi. Next, in step 626, the products are subtracted and added in the form of (Xr*Yr)−(Xi*Yi) and (Xr*Yi)+(Xi*Yr). In step 628, the 32-bit value (Xr*Yr)−(Xi*Yi) is added to the contents of the extended precision target register XPRBo∥Rto and the 32-bit value (Xr*Yi)+(Xi*Yr) is added to the contents of the extended precision target register XPRBe∥Rte. The final result is written back to the extended precision target registers at the end of an operation cycle of the MPYCXLXA instruction 600 with a 40-bit real component and a 40-bit imaginary component placed in the target registers such that XPRBo∥Rto contains the 40-bit real component and XPRBe∥Rte contains the 40-bit imaginary component. For a two cycle embodiment, the target registers are fetched on the second cycle of execution to allow repetitive pipelining to a single accumulation register even-odd pair.
The extended precision bits for the 40-bit results are provided by the extended precision register (XPR). The specific sub-registers used in an extended precision operation depend on the size of the accumulation (dual 40-bit or single 80-bit) and on the target CRF register pair specified in the instruction. For dual 40-bit accumulation, the 8-bit extension registers XPR.B0 and XPR.B1 (or XPR.B2 and XPR.B3) are associated with a pair of CRF registers. For single 80-bit accumulation, the 16-bit extension register XPR.H0 (or XPR.H1) is associated with a pair of CRF registers. During the dual 40-bit accumulation, the even target register is extended using XPR.B0 or XPR.B2, and the odd target register is extended using XPR.B1 or XPR.B3. The tables 602, 604, 608, 612 and 614 of FIG. 6A illustrate the register usage in detail.
As shown in FIG. 6A, the XPR byte that is used depends on the Rte. Further details of an XPR register suitable for use with the present invention are provided in U.S. patent application Ser. No. 09/599,980 entitled “Methods and Apparatus for Parallel Processing Utilizing a Manifold Array (ManArray) Architecture and Instruction Syntax” filed on Jun. 20, 2000 which is incorporated by reference herein in its entirety.
FIG. 7A shows a multiply complex conjugate long extended precision accumulate (MPYCXJLXA) instruction 700 for the multiplication of a first complex number and the conjugate of a second complex number to form a product which is accumulated with the contents of the extended precision target registers in accordance with the present invention. The syntax and operation description 710 of the MPYCXJLXA instruction 700 are shown in FIGS. 7B and 7C. As seen in diagram 720 of FIG. 7C, the MPYCXJLXA instruction 700 provides for the multiplication of two complex numbers stored in source register Rx and source register Ry. In step 722, the complex numbers to be multiplied are organized in the source registers such that H1 contains the real component of the complex numbers and H0 contains the imaginary component of the complex numbers. In step 724, the complex numbers are multiplied to produce the products Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi. Next, in step 726, the products are subtracted and added in the form of (Xr*Yr)+(Xi*Yi) and (Xi*Yr)−(Xr*Yi). In step 728, the 32-bit value (Xr*Yr)+(Xi*Yi) is added to the contents of the extended precision target register XPRBe∥Rte and the 32-bit value (Xi*Yr)−(Xr*Yi) is added to the contents of the extended precision target register XPRBo∥Rto. The final result is written back to the extended precision target registers at the end of an operation cycle of the MPYCXJLXA instruction 700 with a 40-bit real component and a 40-bit imaginary component placed in the target registers such that XPRBo∥Rto contains the 40-bit real component and XPRBe∥Rte contains the 40-bit imaginary component. For a two cycle embodiment, the target registers are fetched on the second cycle of execution to allow repetitive pipelining to a single accumulation register even-odd pair.
The extended precision bits for the 40-bit results are provided by the extended precision register (XPR). The specific sub-registers used in an extended precision operation depend on the size of the accumulation (dual 40-bit or single 80-bit) and on the target CRF register pair specified in the instruction. For dual 40-bit accumulation, the 8-bit extension registers XPR.B0 and XPR.B1 (or XPR.B2 and XPR.B3) are associated with a pair of CRF registers. For single 80-bit accumulation, the 16-bit extension register XPR.H0 (or XPR.H1) is associated with a pair of CRF registers. During the dual 40-bit accumulation, the even target register is extended using to XPR.B0 or XPR.B2, and the odd target register is extended using XPR.B1 or XPR.B3. The tables 702, 704, 708, 712 and 714 of FIG. 7A illustrate the register usage in detail. As shown in FIG. 7A, the XPR byte that is used depends on the Rte.
All of the above instructions 200, 300, 400, 500, 600 and 700 may complete in 2 cycles and are pipelineable. That is, another operation can start executing on the execution unit after the first cycle. In accordance with another aspect of the present invention, all of the above instructions 200, 300, 400, 500, 600 and 700 may complete in a single cycle.
FIG. 8 shows a high level view of a hardware apparatus 800 suitable for implementing the multiply complex instructions for execution in two cycles of operation. This hardware capability may be advantageously embedded in the ManArray multiply accumulate unit (MAU), one of the execution units 131 of FIG. 1 and in each PE, along with other hardware capability supporting other MAU instructions. As a pipelined operation, the first execute cycle begins with a read of source register operands Ry.H1, Ry.H0, Rx.H1 and Rx.H0 from the compute register file (CRF) shown as registers 803 and 805 in FIG. 8 and as registers 111, 127, 127′, 127′′, and 127′′′ in FIG. 1. These operands may be viewed as corresponding to the operands Yr, Yi, Xr and Xi described above. The operand values are input to multipliers 807, 809, 811 and 813 after passing through multiplexer 815 which aligns the halfword operands.
Multipliers 807 and 809 are used as 16×16 multipliers for these complex multiplications. The 32×16 notation indicates these two multipliers are also used to support 32×32 multiplies for other instructions in the instruction set architecture (ISA). Multiplexer 815 is controlled by an input control signal 817. The outputs of the multipliers, Xr*Yr, Xr*Yi, Xi*Yr and Xi*Yi, are input to registers 824a, 824b, 824c and 824d after passing through multiplexer 823 which aligns the outputs based on the type of multiplication operation. The registers 824a, 824b, 824c and 824d latch the multiplier outputs, allowing pipelined operation of a second instruction to begin. An output control signal 825 controls the routing of the multiplier outputs to the input registers 824a, b, c, d of adders 819 and 821. The second execute cycle, which can occur while a new multiply complex instruction is using the first cycle execute facilities, begins with adders 819 and 821 operating on the contents of registers 824a, 824b, 824c and 824d. The adders 819 and 821 function as either adders or subtractors based on a conjugate select signal 827, which is set depending on the type of complex multiplication being executed.
The outputs of the adders 819 and 821 are then passed to accumulators 833 and 835. If an accumulate operation is not being performed, a zero value is output from multiplexers 829 and 831 to accumulators 833 and 835 to produce a zero input for no accumulation. If an accumulate operation is being performed, the contents of current target registers Rt.H1 and Rt.H1, shown as registers 837 and 839, is output from multiplexers 829 and 831 to accumulators 833 and 835 as an input to produce an accumulated result. Multiplexers 829 and 831 are controlled by an accumulator control signal 841. The outputs of the accumulators 823 and 825 are then written to the target registers 837 and 839 which contain the 32 bit real result and the 32 bit imaginary result, respectively.
If an extended precision operation is being performed, the accumulation is augmented eight extra bits by adding the contents of an extended precision registers 843 and 844 to the sign extended output of adders 819 and 821. The outputs of the accumulators 833 and 835 are then written back to the target registers 837 and 839, and the XPR registers 843 and 844, such that registers 843 and 837 contain one of the 40 bit results and registers 844 and 839 contain the other 40 bit result. Real and imaginary results are specified by instructions.
FIG. 9 shows an integrated product adder and accumulator (IPAA) 900 in accordance with the present invention. IPAA 900 may be suitably utilized with hardware 800, replacing an adder and accumulator, to decrease delay and improve performance. For instructions not requiring an accumulated result, select signal 902 controls multiplexer 904 to input a zero value 910 to IPAA 900 which performs addition or subtraction on product operands 906 and 908. For instructions requiring an accumulated result, select signal 902 controls multiplexer 904 to input an accumulated input 912 to IPAA 900 which performs addition or subtraction on product operands 906 and 908 to produce an accumulated result.
FIG. 10 shows a high level view of a hardware apparatus 800′ suitable for implementing the multiply complex instructions for execution in a single cycle of operation. Hardware apparatus 800′ includes many of the same elements as hardware apparatus 800, with common elements to both embodiments designated by the same element numbers. The multiplier alignment multiplexer 823 and registers 824a, 824b, 824c and 824d of apparatus 800 are replaced by a logical array 850, allowing the multiply complex instructions to complete in a single cycle of operation. The logical array 850 properly aligns the outputs of multipliers 807, 809, 811 and 813 for transmission to the adders 819 and 821.
Computation of a Covariance Matrix
The multiply complex long instructions of the present invention may be advantageously used in the computation of a covariance matrix. As an example, consider an antenna array consisting of several elements arranged in a known geometry. Each element of the array is connected to a receiver that demodulates a signal and produces a complex-valued output. This complex-valued output is sampled periodically to produce a discrete sequence of complex numbers. The elements from this sequence may be organized into a vector of a certain length, called a frame, and may be combined with the vectors produced from the remainder of the antenna elements to form a matrix.
For an antenna array with M elements and K samples per frame, a matrix U is created.



  
    
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                  ⁢
                  
                    
                      u
                      
                        M
                        -
                        1
                      
                    
                    ⁡
                    
                      (
                      1
                      )
                    
                  
                  ⁢
                  
                    
                  
                  ⁢
                  ...
                  ⁢
                  
                    
                  
                  ⁢
                  
                    
                      u
                      
                        M
                        -
                        1
                      
                    
                    ⁡
                    
                      (
                      
                        K
                        -
                        1
                      
                      )
                    
                  
                
                ]
              
            
          
        
      
      ]
    
  




  
    
      R
      
        M
        ×
        M
      
    
    =
    
      U
      ×
      
        U
        H
      
    
  



In problems such as direction of arrival algorithms, it is necessary to compute the covariance matrix from such received data. For zero-mean, complex valued data, the covariance matrix, R, is defined to be
where ‘H’ is the hermitian operator, denoting a complex conjugate matrix transpose.
For example, assuming M=12 and K=128, the elements of R are computed as




  
    
      R
      
        i
        ,
        j
      
    
    =
    
      
        ∑
        
          k
          =
          0
        
        
          K
          -
          1
        
      
      ⁢
      
        
          
            u
            i
          
          ⁡
          
            (
            k
            )
          
        
        ×
        
          
            (
            
              
                u
                j
              
              ⁡
              
                (
                k
                )
              
            
            )
          
          *
        
      
    
  
  ,




which corresponds to the summation of 128 complex conjugate multiplies for each of the 144 elements of R. As seen in FIG. 11A, R is a 12×12 matrix 1100. R is conjugate-symmetric, so the upper triangular portion of R is the complex conjugate of the lower triangular portion. Ri,j=Rj,i* for i≠j. As seen in FIG. 11B, this symmetry allows an optimization such that only 78 elements of R, the lower triangular portion and the main diagonal, need to be computed, as the remaining elements are the conjugated copies of the lower diagonal.

Each element in U is represented as a 16-bit, signed (15 information bits and 1 sign bit), complex value (16-bit real, 16-bit imaginary). Fixed-point algebra shows that the multiplication of two such values will result in a complex number with a 31-bit real and 31-bit imaginary component (30 information bits and 1 sign bit). The accumulation of 128 31-bit complex numbers, to avoid saturation (achieving the maximum possible positive or minimum possible negative value available for the given number of bits), requires 39 bits of accuracy in both real and imaginary components (38 information bits and 1 sign bit). Therefore to compute the covariance matrix for this system, it is necessary to utilize the complex multiply-accumulate function that achieves 31 complex bits of accuracy for the multiply, and can accumulate these values to a precision of at least 39 complex signed bits.
The computation of the 78 elements of the covariance matrix 1100 may be advantageously accomplished with the ManArray 2×2 iVLIW SIMD processor 100 shown in FIG. 1. Utilizing the single cycle pipeline multiply complex conjugate long with extended precision accumulate (MPYCXJLXA) instruction described above, 128 complex multiplies can be executed in consecutive cycles. As the iVLIW processor 100 allows 64 bits to be loaded into each PE per cycle, the computation of a single length 128 complex conjugate dot product is accomplished in 130 cycles, for a 2 cycle MPYCXJLXA. For a single cycle MPYCXJLXA, the computation is performed in 129 cycles.
FIGS. 11C-11I show the computations performed by the 4 PEs (PE0, PE1, PE2 and PE3) of processor 100 to calculate the 78 elements of the covariance matrix R 1100. As seen in FIG. 11C, for iteration 1 PE0 performs the multiplications for R0,0, PE1 performs the multiplications for R1,1, PE2 performs the multiplications for R2,2, and PE3 performs the multiplications for R3,3. As seen in FIG. 11D, for iteration 2 PE0 performs the multiplications for R4,4, PE1 performs the multiplications for R5,5, PE2 performs the multiplications for R6,6, and PE3 performs the multiplications for R7,7. As seen in FIG. 11E, for iteration 3 PE0 performs the multiplications for R8,8, PE1 performs the multiplications for R9,9, PE2 performs the multiplications for R10,10, and PE3 performs the multiplications for R11,11. FIGS. 11F-H show the multiplications for iterations 4-11, 12-15, 16-18 and 19-20, respectively. Thus, the computation of the 78 elements of the covariance matrix from a 12×128 data matrix of 16-bit signed complex numbers occurs in 20 (dot product iterations)×130 (cycles per dot product)=2600 cycles, plus a small amount of overhead. The remaining elements of R are simply the conjugated copies of the lower diagonal. Prior art implementations typically would consume 79,872 cycles on a single processor with 8 cycles per complex operation, 128 complex operations per dot product and 78 dot products.
While the present invention has been disclosed in the context of various aspects of presently preferred embodiments, it will be recognized that the invention may be suitably applied to other environments consistent with the claims which follow.

## Claims

1. An apparatus for extending the precision of a complex multiplication with accumulation, the apparatus comprising:
a reduced precision storage unit for storing at least two complex operands, a reduced-precision real value, and a reduced-precision imaginary value;
an extended-precision storage unit for holding an extended-precision real component and an extended-precision imaginary component;
multipliers for multiplication of the two complex operands accessed from the reduced-precision storage unit to produce real and imaginary components of a complex product;
a first integrated product adder and accumulator (IPAA) for addition and subtraction of real and imaginary components of the complex product combined with addition of an extended-precision real value producing an accumulated real result, the extended-precision real value formed by a concatenation of the extended-precision real component with the reduced-precision real value, and the accumulated real result made available for storing back an updated extended-precision real component in the extended-precision storage unit and an updated reduced-precision real value in the reduced-precision storage unit; and
a second integrated product adder and accumulator (IPAA) for addition and subtraction of real and imaginary components of the complex product combined with addition of an extended-precision imaginary value producing an accumulated imaginary result, the extended-precision imaginary value formed by a concatenation of the extended-precision imaginary component with the reduced-precision imaginary value, and the accumulated imaginary result made available for storing back an updated extended-precision imaginary component in the extended-precision storage unit and an updated reduced-precision imaginary value in the reduced-precision storage unit.

2. An apparatus according to claim 1 wherein the reduced-precision storage unit further comprises:
a selectable odd-numbered addressable storage for storing the updated reduced-precision real value; and
a selectable even-numbered addressable storage for storing the updated reduced-precision imaginary value.

3. The apparatus of claim 2 wherein the extended-precision storage unit further comprises:
a selectable odd-numbered addressable storage associated with the selectable odd-numbered addressable storage of the reduced-precision storage unit for storing the updated extended-precision real component; and
a selectable even-numbered addressable storage associated with the selectable even-numbered addressable storage of the reduced-precision storage unit for storing the updated extended-precision imaginary component.

4. The apparatus of claim 2 wherein the selectable odd-numbered addressable storage further comprises:
a byte from byte position 1 of bytes 0, 1, 2, and 3 associated with a selected addressable storage of the reduced-precision storage unit being one storage address from every other odd storage address beginning at 1 for storing the updated extended-precision real component; and
a byte from byte position 3 of bytes 0, 1, 2, and 3 associated with a selectable addressable storage of the reduced-precision storage unit being one storage address from every other odd storage address beginning at 3 for storing the updated extended-precision real component.

5. The apparatus of claim 2 wherein the selectable even-numbered addressable storage further comprises:
a byte from byte position 0 of bytes 0, 1, 2, and 3 associated with a selected addressable storage of the reduced-precision storage unit being one storage address from every other even storage address beginning at 0 for storing the updated extended-precision imaginary component; and
a byte from byte position 2 of bytes 0, 1, 2, and 3 associated with a selectable addressable storage of the reduced-precision storage unit being one storage address from every other even storage address beginning at 2 for storing the updated extended-precision imaginary component.

6. A method for extending the precision of a complex multiplication with accumulation in a processor, the method comprising:
multiplying two complex number operands accessed from a reduced precision storage unit to produce four real and imaginary components of a complex product in response to a processor issued multiply complex with extended precision accumulate instruction;
adding two selected real and imaginary components of the complex product to produce a real result;
subtracting two remaining selected real and imaginary components of the complex product to produce an imaginary result;
adding an extended-precision real value with the real result to produce an accumulated real result, the extended-precision real value formed by a concatenation of an extended-precision real component stored in an extended-precision storage unit with a reduced-precision real value stored in a reduced precision storage unit, and the accumulated real result made available for storing back an updated extended-precision real component in the extended-precision storage unit and an updated reduced-precision real value in the reduced-precision storage unit; and
adding an extended-precision imaginary value with the imaginary result to produce an accumulated imaginary result, the extended-precision imaginary value formed by a concatenation of an extended-precision imaginary component stored in an extended-precision storage unit with a reduced-precision imaginary value stored in a reduced precision storage unit, and the accumulated imaginary result made available for storing back an updated extended-precision imaginary component in the extended-precision storage unit and an updated reduced-precision imaginary value in the reduced-precision storage unit.

7. The method of claim 6 further comprising:
receiving a multiply complex long extended precision accumulate (MPYCXLXA) instruction; and
executing the MPYCXLXA instruction to extend the precision of the complex multiplication with accumulation result.

8. The method of claim 7 wherein the MPYCXLXA instruction is received in parallel in a plurality of processing elements (PE) for execution in parallel.

9. The method of claim 7 further comprising:
storing in an intermediate set of registers the four real and imaginary components of a complex product produced at the end of a first pipeline cycle; and
storing the accumulated real result and the accumulated imaginary result in program accessible target registers produced at the end of a second pipeline cycle, wherein a second MPYCXLXA instruction is started to execute in the first pipeline cycle while a first MPYCXLXA instruction is started to execute in the second pipeline cycle.

10. A method for extending the precision of a complex conjugate multiplication with accumulation for the execution of a multiply complex conjugate long extended precision accumulate (MPYCXJLXA) instruction in a processor, the method comprising:
multiplying two complex number operands accessed from a reduced precision storage unit to produce four real and imaginary components of a complex product in response to a processor issued MPYCXJLXA instruction;
adding two selected real and imaginary components of the four real and imaginary components of the complex product to produce a conjugate real result;
subtracting two remaining selected real and imaginary components of the four real and imaginary components of the complex product to produce a conjugate imaginary result;
adding an extended-precision real value with the conjugate real result to produce an accumulated conjugate real result, the extended-precision real value formed by a concatenation of an extended-precision real component stored in an extended-precision storage unit with a reduced-precision real value stored in a reduced precision storage unit, and the accumulated conjugate real result made available for storing back an updated extended-precision real component in the extended-precision storage unit and an updated reduced-precision real value in the reduced-precision storage unit; and
adding an extended-precision imaginary value with the imaginary result to produce an accumulated conjugate imaginary result, the extended-precision imaginary value formed by a concatenation of an extended-precision imaginary component stored in an extended-precision storage unit with a reduced-precision imaginary value stored in a reduced precision storage unit, and the accumulated conjugate imaginary result made available for storing back an updated extended-precision imaginary component in the extended-precision storage unit and an updated reduced-precision imaginary value in the reduced-precision storage unit.

11. The method of claim 10, further comprising:
providing a data array UM×K having M elements and K samples, wherein each element in U comprises a 16 bit real value and a 16 bit complex value; and
executing the MPYCXJLXA instruction M times to calculate a first element R of a covariance matrix RM×M=U×UH.

12. The method of claim 11 wherein the MPYCXJLXA instruction is pipelineable.

13. The method of claim 11 wherein the first element of R is at least 39 complex signed bits.

14. The method of claim 11 wherein the MPYCXJLXA instruction completes execution in 2 cycles.

15. The method of claim 11 wherein the MPYCXJLXA instruction completes execution in a single cycle.

16. The method of claim 11 wherein the step of calculating a first element further comprises the steps of:
initiating a first execution the MPYCXJLXA instruction in a first cycle; and
initiating a second execution of a second MPYCXJLXA instruction in a second cycle, the second cycle immediately following the first cycle.

17. The method of claim 11 further comprising the step of:
calculating a second element of R utilizing the MPYCXJLXA instruction which executes M times.

18. The method of claim 17 wherein the step of calculating a first element utilizes a first processing element (PE) of an array of PEs and the step of calculating a second element utilizes a second PE and both the step of calculating a first element and the step of calculating a second element occur simultaneously.

19. The method of claim 10 wherein:
each of the two complex number operands are n/2 bits,
the reduced-precision real value and the reduced-precision imaginary value are each n bits,
the extended-precision real component is n/4 bits, and
the extended-precision imaginary component is n/4 bits.

20. The method of claim 10 further comprising:
executing a multiply complex conjugate long (MPYCXJL) instruction by inserting a zero in place of the extended-precision real value and in place of the extended-precision imaginary value;
storing back the accumulated conjugate real result in the reduced-precision storage unit without storing back an updated extended-precision real component in the extended-precision storage unit; and
storing back the accumulated conjugate imaginary result in the reduced-precision storage unit without storing back an updated extended-precision imaginary component in the extended-precision storage unit.