Abstract:
A computer machine instruction is fetched and executed, the machine instruction having a signed field value wherein the signed field value comprises contiguous bit positions  1 -N consisting of a contiguous most significant value contiguous with a contiguous embedded sign field, the embedded sign field contiguous with a contiguous least significant value. Preferably, the sign field is one bit, the contiguous most significant value comprises bit position N and the least significant value comprises bit position  1  wherein N is the least significant bit of the most significant value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This is a divisional application of Ser. No. 10/403,417 “Long Displacement Instruction Formats” filed on Mar. 28, 2003 and assigned to IBM. The disclosure of the forgoing application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to computer systems, and particularly to a computer architecture having signed values wherein the sign is embedded between magnitude value portions.  
       BACKGROUND  
       [0003]     Trademarks: IBM® is a registered trademark of International Business Machines Corporation, Armonk, N.Y., U.S.A. S/390, Z900 and z990 and other product names may be registered trademarks or product names of International Business Machines Corporation or other companies.  
         [0004]     Before our invention there existed in the IBM Z/Architecture (and its predecessor architectures) the existence of instruction formats having storage addressing in the form of base register plus 12 bit unsigned displacement or the form of base register plus index register plus 12 bit unsigned displacement, as incorporated in IBM&#39;s z900 mainframe servers. Generally, the computer architecture of the z900 was described in the IBM Z/Architecture Principles of Operation, Publication SA22-7832-00 (incorporated herein by reference), where section 5-2 to 5-7 describes the Instructions consisting of two major parts: an op code and the designation of the operands that participate. The instruction formats of these currently available machines are described beginning at 5-3. It will be noted that the basic instruction formats described at 5-4 and 5-5 include the RXE format described in detail also in our prior U.S. Pat. No. 6,105,126, granted Aug. 15, 2000, and entitled “Address Bit Decoding for same Adder Circuitry for RXE Instruction Format with SAME XBD location as RX Format and Disjointed Extended Operation Code.” 
       SUMMARY OF THE INVENTION  
       [0005]     In accordance with our preferred embodiment of our invention for use on both the prior IBM z900 Servers, but also on new processors which we name the z990 Servers, as well as on other computer systems which can emulate our new IBM Z/Architecture comprising of the existing Z/Architecture instructions and instruction formats and new instructions using several new long displacement instruction formats that provide for a new storage addressing that consists of either base register plus 20 bit signed displacement or base register plus index register plus 20 bit signed displacement. These new formats can be used to provide new instructions or can modify the operation of a subset of existing instructions that were created with only the prior 12 bit unsigned displacements for calculation of the storage address. The advantages achieved by the new computer architecture instruction formats is that they provide for a long displacement facility which can be achieved within an existing machine or a new machine which implements the new Z/Architecture with our new instruction formats.  
         [0006]     It is therefore an object of the invention to execute a machine instruction in a central processing unit by fetching a signed displacement machine instruction for execution, the signed displacement machine instruction defined for computer execution according to a computer architecture, the signed displacement machine instruction comprising an opcode field and an signed displacement field having N contiguous bits consisting of a signed displacement value, the signed displacement value consisting of a magnitude and a sign S, the signed displacement value consisting of N contiguous bit positions  1  through N wherein the magnitude consists of a first value consisting of contiguous bit positions  1  through S−1 and a second value consisting of bit positions S+1 through N wherein bit position S is greater than 1 and less than N. Then extracting a magnitude value from the signed displacement value magnitude and extracting the sign S from the signed displacement value whereby the extracted sign S and magnitude value is used to perform a function defined by the opcode field.  
         [0007]     It is another object of the invention to perform the extracting step by concatenating the first value with the second value to form the magnitude value the second value consists of least significant bits of the magnitude value the first value consists of most significant bits of the magnitude value.  
         [0008]     It is yet another object of the invention to concatenate the sign S with the most significant bit position of the magnitude value to form a signed magnitude value, then using the signed magnitude value in the using step to perform a function defined by the opcode field, wherein the function.  
         [0009]     It is still another object of the invention to obtain an operand base address from a location specified by an operand base address field of the signed displacement machine instruction and if the sign S is negative, arithmetically subtracting the magnitude value from the operand base address to determine an address of an operand but if the sign S is positive, arithmetically adding the magnitude value to the operand base address to determine the address of the operand and finally, to perform the function defined by the opcode field, wherein the function uses the operand at the determined address.  
         [0010]     It is another object of the invention to further fetch an unsigned displacement machine instruction for execution, the unsigned displacement machine instruction defined for computer execution according to the computer architecture, the unsigned displacement machine instruction comprising an opcode field and an unsigned displacement field having S−1 contiguous bits consisting of an unsigned displacement value, the unsigned displacement value consisting of an unsigned magnitude consisting of contiguous bit positions  1  through S−1, wherein bit positions  1  through S−1 consist of the same bit positions as bit positions  1  through S−1 of the signed displacement machine instruction and extract an unsigned magnitude value from the unsigned displacement value and to use the unsigned magnitude value to perform a the function defined by the opcode field. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  illustrates the existing Z/Architecture RXE instruction format;  
         [0012]      FIG. 2  illustrates the existing Z/Architecture RSE instruction format;  
         [0013]      FIG. 3  illustrates the new Z/Architecture RXY instruction format;  
         [0014]      FIG. 4  illustrates the new Z/Architecture RSY instruction format;  
         [0015]      FIG. 5  illustrates the new Z/Architecture SIY instruction format; and  
         [0016]      FIG. 6 , shows the preferred embodiment of a computer memory storage containing instructions in accordance with the preferred embodiment and data, as well as the mechanism for fetching, decoding and executing these instructions, either on a computer system employing these architected instructions or as used in emulation of our architected instructions.  
     
    
       [0017]     Our detailed description explains the preferred embodiments of our invention, together with advantages and features, by way of example with reference to the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     In the current Z/Architecture there exist the RXE format as described in U.S. Pat. No. 6,105,126 (incorporated fully by reference) shown here and in that patent as  FIG. 1 , and also RSE, shown here as  FIG. 2 , instruction formats. There are existing instructions in the Z/Architecture which use the base register plus 12 unsigned displacement or base register plus index register plus 12 bit unsigned displacement to form the operand storage address.  
         [0019]     In accordance with our preferred embodiment the invention creates three new formats RXY,  FIG. 3 , RSY,  FIG. 4 , and SIY,  FIG. 5 . These new formats are used to provide a 20 bit signed displacement field that can be used to form the operand storage address base register plus 20 bit signed displacement or base register plus index register plus 20 bit signed displacement. This new 20 bit signed displacement field can be used for support of new instructions or can allow prior instructions that only had a 12 bit unsigned displacement to now have access to a signed 20 bit signed displacement. It is a feature of our invention that any software code created under the prior instruction formats will operate as they were originally defined, with a 12 bit unsigned displacement, while especially, any new software code created under the new instruction formats can operate with the new 20 bit signed displacement (chosen as comprising signed long displacement bits numbering, in the preferred embodiment 20). The new 20 bit signed displacement is done as two parts that are adjacent to each other. The two parts of the displacement value while being located in adjacent fields in the instruction text are not sequentially numbered bit ranges. The DL1 or DL2 field in the instruction formats is the least significant 12 bits of the 20 bit signed displacement and are in the same location in the RXY, RSY, and SIY instruction formats as the 12 bit unsigned D2 field in the existing RXE and RSE formats. The DH1 or DH2 field in the RXY, RSY, or SIY instruction formats are defined as the 8 most significant bits of the 20 bit signed displacement field and is located in an undefined area of the RXE and RSE instruction formats. By reference to the Figures it will be appreciated that D 1  and D 2  refers to the displacement field for operand one and the displacement field for operand two of an instruction while, as DL is an acronym for “Displacement Low” while DH is an acronym for “Displacement High” for which it will be appreciated that DL 1  and DH 1  will refer to the displacement fields for operand one and DL 2  and DH 2  will refer to the displacement fields for operand two.  
         [0020]     In  FIG. 6 , # 501  shows a computer memory storage containing instructions and data. The long displacement instructions described in this invention would initially stored in this computer. # 502  shows a mechanism for fetching instructions from a computer memory and may also contain local buffering of these instructions it has fetched. Then the raw instructions are transferred to an instruction decoder, # 503 , where it determines what type of instruction has been fetched. # 504 , shows a mechanism for executing instructions. This may include loading data into a register from memory, # 501 , storing data back to memory from a register, or performing some type of arithmetic or logical operation. This exact type of operation to be performed has been previously determined by the instruction decoder. The long displacement instructions described in this invention would be executed here. If the long displacement instructions are being executed natively on a computer system, then this diagram is complete as described above. However, if an instruction set architecture, containing long displacement instructions, is being emulated on another computer, the above process would be implemented in software on a host computer, # 505 . In this case, the above stated mechanisms would typically be implemented as one or more software subroutines within the emulator software. In both cases an instruction is fetched, decoded and executed.  
         [0021]     More particularly, these architected instructions can be used with a computer architecture with existing instruction formats with a 12 bit unsigned displacement used to form the operand storage address and also one having additional instruction formats that provide a additional displacement bits, preferably 20 bits, which comprise an extended signed displacement used to form the operand storage address. These computer architected instructions comprise computer software, stored in a computer storage medium, for producing the code running of the processor utilizing the computer software, and comprising the instruction code for use by a compiler or emulator/interpreter which is stored in a computer storage medium  501 , and wherein the first part of the instruction code comprises an operation code which specified the operation to be performed and a second part which designates the operands for that participate. The long displacement instructions permit additional addresses to be directly addressed with the use of the long displacement facility instruction.  
         [0022]     In a commercial implementation of the long displacement facility computer architected instruction format the instructions are used by programmers, usually today “C” programmers. These instruction formats stored in the storage medium may be executed natively in a Z/Architecture IBM Server, or alternatively in machines executing other architectures. They can be emulated in the existing and in future IBM mainframe servers and on other machines of IBM (e.g. pSeries Servers and xSeries Servers). They can be executed in machines running Linux on a wide variety of machines using hardware manufactured by IBM, Intel, AMD, Sun Microsystems and others. Besides execution on that hardware under a Z/Architecture, Linux can be used as well as machines which use emulation by Hercules, UMX, FXI or Platform Solutions, where generally execution is in an emulation mode. In emulation mode the specific instruction being emulated is decoded, and a subroutine built to implement the individual instruction, as in a “C” subroutine or driver, or some other method of providing a driver for the specific hardware as is within the skill of those in the art after understanding the description of the preferred embodiment. Various software and hardware emulation patents including, but not limited to U.S. Pat. No. 5,551,013 for a “Multiprocessor for hardware emulation” of Beausoleil et al., and U.S. Pat. No. 6,009,261: Preprocessing of stored target routines for emulating incompatible instructions on a target processor” of Scalzi et al; and U.S. Pat. No. 5,574,873: Decoding guest instruction to directly access emulation routines that emulate the guest instructions, of Davidian et al; U.S. Pat. No. 6,308,255: Symmetrical multiprocessing bus and chipset used for coprocessor support allowing non-native code to run in a system, of Gorishek et al; and U.S. Pat. No. 6,463,582: Dynamic optimizing object code translator for architecture emulation and dynamic optimizing object code translation method of Lethin et al; and U.S. Pat. No. 5,790,825: Method for emulating guest instructions on a host computer through dynamic recompilation of host instructions of Eric Traut; and many others, illustrate the a variety of known ways to achieve emulation of an instruction format architected for a different machine for a target machine available to those skilled in the art, as well as those commercial software techniques used by those referenced above.  
         [0023]     In the preferred embodiment the existing instruction formats form the operand storage address by the summing of the base register and 12 bit unsigned displacement or the base register, the index register, and the 12 bit unsigned displacement and the new instruction formats form the operand storage address by the summing of the base register and the 20 bit signed displacement or the base register, the index register, and the 20 bit signed displacement.  
         [0024]     As illustrated by  FIG. 6 , these instructions are executed in hardware by a processor or by emulation of said instruction set by software executing on a computer having a different native instruction set.  
         [0025]     In accordance with the computer architecture of the preferred embodiment the displacement field is defined as being in two parts, the least significant part being 12 bits called the DL, DL 1  for operand  1  or DL 2  for operand  2 , and the most significant part being 8 bits called the DH, DH 1  for operand  1  or DH 2  for operand  2 .  
         [0026]     Furthermore, the preferred computer architecture has an instruction format such that the opcode is in bit positions  0  through  7  and  40  through  47 , a target register called R 1  in bit positions  8  through  11 , an index register called X 2  in bit positions  12  through  15 , a base register called B 2  in bit positions  16  through  19 , a displacement composed of two parts with the first part called DL 2  in bit positions  20  through  31  and the second part called DH 2  in bit positions  32  through  39 .  
         [0027]     This computer architecture has an instruction format such that the opcode is in bit positions  0  through  7  and  40  through  47 , a target register called R 1  in bit positions  8  through  11 , an source register called R 3  in bit positions  12  through  15 , a base register called B 2  in bit positions  16  through  19 , a displacement composed of two parts with the first part called DL 2  in bit positions  20  through  31  and the second part called DH 2  in bit positions  32  through  39 .  
         [0028]     Furthermore, our computer architecture instructions having a long displacement facility has an instruction format such that the opcode is in bit positions  0  through  7  and  40  through  47 , a target register called R 1  in bit positions  8  through  11 , a mask value called M 3  in bit positions  12  through  15 , a base register called B 2  in bit positions  16  through  19 , a displacement composed of two parts with the first part called DL 2  in bit positions  20  through  31  and the second part called DH 2  in bit positions  32  through  39 .  
         [0029]     AS illustrated, our preferred computer architecture with its long displacement facility has an instruction format such that the opcode is in bit positions  0  through  7  and  40  through  47 , an immediate value called  12  in bit positions  8  through  15 , a base register called B 2  in bit positions  16  through  19 , a displacement composed of two parts with the first part called DL 1  in bit positions  20  through  31  and the second part called DH 1  in bit positions  32  through  39 .  
         [0030]     Our long displacement facility computer architecture operates effectively when using new instructions which are created that only use the instruction format with the new 20 bit unsigned displacement.  
         [0031]     A specific embodiment of our computer architecture utilizes existing instructions which have the instruction formats that only have the 12 bit unsigned displacement and are now defined to be in the new instruction formats to have either the existing 12 bit unsigned displacement value when the high order 8 bits of the displacement, field DH, are all zero, or a 20 bit signed value when the high order 8 bits of the displacement, field DH, is non-zero.  
         [0032]     While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.