Instructions to load and store containing words in a computer system emulator with host word size larger than that of emulated machine

Abstract

Two unique instructions for the instruction set of a target 36-bit machine which is emulated on a host 64-bit machine are provided in order to achieve visibility, to an emulated application program, of a 'containing' word stored in the memory of the host machine. A 'LOAD64' instruction loads the emulator memory location representing an emulated “Q” (supplementary accumulator) register with the “normal” 36-bits of the containing word. At the same time, the “upper” 28 bits of the 64-bit containing word is copied into the emulator memory location representing an emulated “A” (accumulator) register. Thus, the emulated 36-bit machine “sees” and can examine the 64-bit word in its entirety. A “Store64” instruction stores the emulated “Q” register contents into the lower 36-bits of the 64-bit containing word, and at the same time stores the lower 28 bits of the emulated “A” register contents into the upper 28 bits of the 64-bit containing word.