Decimal floating-point in z9: An implementation and testing perspective

Although decimal arithmetic is widely used in commercial and financial applications, the related computations are handled in software. As a result, applications that use decimal data may experience performance degradations. Use of the newly defined decimal floating-point (DFP) format instead of binary floating-point is expected to significantly improve the performance of such applications. System z9™ is the first IBM machine to support the DFP instructions. We present an overview of this implementation and provide some measurement of the performance gained using hardware assists. Various tools and techniques employed for the DFP verification on unit, element, and system levels are presented in detail. Several groups within IBM collaborated on the verification of the new DFP facility, using a common reference model to predict DFP results.