Importance

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Abstract

In a computing system of the type which executes instructions having the form A op B=B, a floating point register includes a plurality of addressable storage elements for storing operand data. A first address receiving circuit receives the B operand address from a first instruction, and a second address receiving circuit receives the A operand address from the first instruction. The A and B operand addresses are each used for addressing one of the plurality of floating point register storage elements. An instruction executing circuit performs a function designated by the first instruction on the operand data output from the floating point register and generates result data. The instruction executing circuit includes an exception circuit for generating exception data indicating whether an exception occurred when the function was performed. A shift register has a plurality of storage elements for storing address and control information. A first address storing circuit stores the B operand address in a selected one of the plurality of shift register storage elements, and a shift register output circuit outputs the stored first instruction B operand address at approximately the time the result data corresponding to the first instruction is generated by the instruction executing circuit. A floating point register storage control circuit stores the result data corresponding to the first instruction in the floating point register storage element addressed by the stored first instruction B operand address as long as no exception occurred when the function was performed. However, the floating point register storage control circuit inhibits the storage of the result data in the floating point register when an exception does occur so that the old B operand value is not destroyed by a probably erroneous value. An operand queue includes a plurality of storage elements for storing A operand data output by the floating point register, and a trap queue includes a plurality of storage elements for storing A operand data corresponding to an instruction which generated exception data, and A trap queue data storing circuit stores the A operand data output from the operand queue into one of the trap queue storage elements whenever an exception is detected. The instructions which were executing when the first exception is detected are allowed to complete.

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First Claim