IEEE compliant floating point unit

摘要

IEEE compliant floating point unit mechanism allows variability in the execution of floating point operations according to the IEEE 754 standard and allowing variability of the standard to co-exist in hardware or in the combination of hardware and millicode. The FPU has a detector of special conditions which dynamically detects an event that the hardware execution of an IEEE compliant Binary Floating Point instruction will require millicode emulation. The complete set of events which millicode may emulate are predetermined early in the design process of the hardware. An exception handling unit assist millicode emulation by trapping the result of an exceptional condition without invoking the trap handler. When an exceptional condition is detected during execution, the IEEE 754 standard requires two different actions under control of a mask bit. If the mask bit is on, the result is written into an FPR and the trap handler is invoked. Otherwise, a default value is written, a flag is set, and the program continues execution. This allows a variation to the IEEE 754 standard. Two different versions of the function of the Multiply-then-Substract instruction are implemented for two different IEEE 754 compliant architectures.