CFPU: Configurable Floating Point Multiplier for Energy-Efficient Computing.

Many applications, such as machine learning and data sensing are statistical in nature and can tolerate some level of inaccuracy in their computation. Approximate computation is a viable method to save energy and increase performance by trading energy for accuracy. There are a number of proposed approximate solutions, however, they are limited to a small range of applications because they cannot control the error rate of their output. In this paper, we propose a novel approximate floating point multiplier, called CFPU, which significantly reduces energy and improves performance of multiplication at the expense of accuracy. Our design approximately models multiplication by replacing the most costly step of the operation with a lower energy alternative. In order to tune the level of approximation, CFPU dynamically identifies the inputs which will produce the largest approximation error and processes them in precise CFPU mode. We showed that our CFPU can outperforms a standard FPU when at least 4% of multiplications are performed in approximate mode. In our tested applications this percentage of multiplications is substantially higher, leading to significant energy savings. Our experimental evaluation on AMD Southern Island GPU shows that replacing the proposed CFPU with traditional FPUs results in 77% energy savings and 3.5x energy-delay product improvement over eight general OpenCL applications while providing acceptable quality of service. In addition, for the same level of accuracy, the CFPU provides 2.4x energy-delay product improvement compared to state-of-the-art approximate multipliers.