Abstract:
A microprocessor with a floating point unit configured to efficiently allocate multi-pipeline executable instructions is disclosed. Multi-pipeline executable instructions are instructions that are not forced to execute in a particular type of execution pipe. For example, junk ops are multi-pipeline executable. A junk op is an instruction that is executed at an early stage of the floating point unit's pipeline (e.g., during register rename), but still passes through an execution pipeline for exception checking. Junk ops are not limited to a particular execution pipeline, but instead may pass through any of the microprocessor's execution pipelines in the floating point unit. Multi-pipeline executable instructions are allocated on a per-clock cycle basis using a number of different criteria. For example, the allocation may vary depending upon the number of multi-pipeline executable instructions received by the floating point unit in a single clock cycle.
Abstract:
A processor capable of efficiently performing iterative calculations is disclosed. The processor comprises a multiplier that is configured to perform iterative multiplication operations to evaluate constant powers of an operand such as the reciprocal and reciprocal square root. Intermediate products that are formed are compressed and decompressed to reduce interim storage requirements. The intermediate products may be rounded and normalized in two paths, one assuming an overflow will occur, and then compressed and stored for use in the next iteration.
Abstract:
A microprocessor configured to rapidly execute floating point store status word (FSTSW) type instructions that are immediately preceded by floating point compare (FCOM) type instructions is disclosed. FCOM-type instructions are modified to store their results to an architectural floating point status word and a temporary destination register. If an FSTSW-type instruction is detected immediately following an FCOM-type instruction, then the FSTSW-type instruction is transformed into a special fast floating point store status word (FSTSWEF) instruction. Unlike the FSTSW-type instruction, which is serializing and negatively impacts performance, the FSTSWEF instruction is not serializing and allows execution to continue without undue serialization. A computer system and method for rapidly executing FSTSW instructions immediately preceded by FCOM-type instructions are also disclosed.
Abstract:
A multi-function look-up table for determining output values for predetermined ranges of a first mathematical function and a second mathematical function. In one embodiment, the multi-function look-up table is a bipartite look-up table including a first plurality of storage locations and a second plurality of storage locations. The first plurality of storage locations store base values for the first and second mathematical functions. Each base value is an output value (for either the first or second function) corresponding to an input region which includes the look-up table input value. The second plurality of storage locations, on the other hand, store difference values for both the first and second mathematical functions. These difference values are used for linear interpolation in conjunction with a corresponding base value in order to generate a look-up table output value. The multi-function look-up table further includes an address control unit coupled to receive a first input value and a signal which indicates whether an output value is to be generated for the first or second mathematical function. The address control unit then generates a first address value from these signals which is in turn conveyed to the first and second plurality of storage locations. In response to receiving the first address value, the first and second plurality of storage locations are configured to output a first base value and a first difference value, respectively. The first base value and first difference value are then conveyed to an output unit configured to generate a look-up table output value from the two values.
Abstract:
A multimedia execution unit configured to perform vectored floating point and integer instructions. The execution unit may include an add/subtract pipeline having far and close data paths. The far path is configured to handle effective addition operations and effective subtraction operations for operands having an absolute exponent difference greater than one. The close path is configured to handle effective subtraction operations for operands having an absolute exponent difference less than or equal to one. The close path is configured to generate two output values, wherein one output value is the first input operand plus an inverted version of the second input operand, while the second output value is equal to the first output value plus one. Selection of the first or second output value in the close path effectuates the round-to-nearest operation for the output of the adder. The execution unit may be configured to perform vectored addition and subtraction, integer/floating point conversion, reverse subtraction, accumulate, extreme value (minimum/maximum), and comparison instructions.
Abstract:
A method for generating entries for a bipartite look-up table having base and difference table portions. In one embodiment, these entries are usable to form output values for a mathematical function, f(x), in response to receiving corresponding input values within a predetermined input range. The method first comprises partitioning the input range into I intervals, J subintervals/interval, and K sub-subintervals/subinterval. For a given interval M, the method includes generating K difference table entries and J base table entries. Each of the K difference table entries corresponds to a particular group of sub-subintervals within interval M, each of which has the same relative position within their respective subintervals. Each difference table entry is computed by averaging difference values for the sub-subintervals included in a corresponding group N. Each difference value which makes up this average is equal to f(X1)−f(X2), where X1 is the midpoint of the sub-subinterval within group N, and X2 is the midpoint of a predetermined reference sub-subinterval within the same subinterval as X1. Each of these midpoints is calculated such that maximum absolute error is minimized for all possible input values in the sub-subinterval. Each of the J base table entries, on the other hand, corresponds to a subinterval within interval M. Each entry is equal to f(X2)+adjust, where X2 is the midpoint of the reference sub-subinterval of the subinterval corresponding to the base table entry. The adjust value is calculated so that error introduced by the averaging of the difference table entries is evenly distributed over the entire subinterval.
Abstract:
A processor capable of efficiently evaluating constant powers of an operand such as the reciprocal and reciprocal square root is disclosed. The processor comprises a multiplier that is configured to perform iterative multiplication operations to evaluate constant powers of an operand such as the reciprocal and reciprocal square root. Intermediate products that are formed may be rounded and normalized in two paths, one assuming an overflow will occur, and then compressed and stored for use in the next iteration. The processor comprises a multiplier capable of performing signed and unsigned scalar and vector multiplication is disclosed. The multiplier may performing rounded by adding a rounding constant.
Abstract:
In contrast to a conventional computing system in which the graphics processor (graphics processing unit or GPU) is treated as a slave to one or several CPUs, systems and methods are provided that allow the GPU to be treated as a central processing unit (CPU) from the perspective of the operating system. The GPU can access a memory space shared by other CPUs in the computing system. Caches utilized by the GPU may be coherent with caches utilized by other CPUs in the computing system. The GPU may share execution of general-purpose computations with other CPUs in the computing system.
Abstract:
A multimedia execution unit configured to perform vectored floating point and integer instructions. The execution unit may include an add/subtract pipeline having far and close data paths. The far path is configured to handle effective addition operations and effective subtraction operations for operands having an absolute exponent difference greater than one. The close path is configured to handle effective subtraction operations for operands having an absolute exponent difference less than or equal to one. The close path is configured to generate two output values, wherein one output value is the first input operand plus an inverted version of the second input operand, while the second output value is equal to the first output value plus one. Selection of the first or second output value in the close path effectuates the round-to-nearest operation for the output of the adder.
Abstract:
A microprocessor with a floating point unit configured to rapidly execute floating point compare (FCOMI) type instructions that are followed by floating point conditional move (FCMOV) type instructions is disclosed. FCOMI-type instructions, which normally store their results to integer status flag registers, are modified to store a copy of their results to a temporary register located within the floating point unit. If an FCMOV-type instruction is detected following an FCOMI-type instruction, then the FCMOV-type instruction's source for flag information is changed from the integer flag register to the temporary register. FCMOV-type instructions are thereby able to execute earlier because they need not wait for the integer flags to be read from the integer portion of the microprocessor. A computer system and method for rapidly executing FCOMI-type instructions followed by FCMOV-type instructions are also disclosed.