The POWER7 Binary Floating-Point Unit

Abstract

The binary Floating-Point Unit (FPU) of the POWER7 processor is a 5.5 cycle Fused Multiply-Add (FMA) design, fully compliant with the IEEE 754-2008 standard. Unlike previous PowerPC designs, the POWER7 FPU merges the scalar and vector FPUs into a single unit executing three floating-point instruction sets: the single and double precision scalar set, the single precision VMX vector set, and the new single and double precision VSX vector and scalar set. Due to a compact buffer-free floor plan and several optimizations in the data and control flow, the streamlined POWER7 FPU achieves a factor of 2 area reduction over the POWER6 design, beyond the normal technology shrink. This results in a very power and area efficient FPU design, supporting a chip frequency of 4.14GHz. A single 64-bit FPU instance measures only 0.26mm2 in 45nm CMOS SOI.