Quad Precision Floating Point on the IBM z13

Abstract

When operating on a rapidly increasing amount of data, business analytics applications become sensitive to rounding errors, and profit from the higher stability and faster convergence of quad precision floating-point (FP-QP) arithmetic. The IBM z13TM supports this emerging trend around Big Data with an outstanding FP-QP performance. The paper details the vector and floating-point unit of IBM z13TM, with special focus on binary FP-QP. Except for divide and square root, these instructions are executed in the decimal engine. To operate such an 8-cycle decimal and quad precision pipeline at 5GHz required innovation around exponent handling, normalization, and rounding.