Floating point exception prediction for compound operations and variable

Abstract

Exponents are first combined together, in a way that varies with the type of floating point operation. A single intermediate exponent result is placed on an intermediate exponent bus. This intermediate exponent is adjusted upwards for any carry-out from the operation on the mantissas, or downwards for any cancellation of leading mantissa bits, producing the final exponent result. The intermediate exponent on the intermediate exponent bus is also compared to a single criteria which is used for all types of floating point operations. Thus the compare logic may be simplified because only a single set of criteria is used for all types of operations. Alternately, the criteria may be varied depending upon the degree of precision used by all operations. Because the intermediate exponent is used, separate exponent adders are not necessary for the prediction unit and the floating point unit. Compound floating point operations may require more complex logic for combining the exponents. The more complex logic is needed to calculate the exponent for the result, so again no additional logic is needed for prediction. Only a single exponent is outputted to the intermediate exponent bus. Thus compound floating point operations may be accommodated simply with the modifications needed for the exponent combination logic.