FlexFloat: A Software Library for Transprecision Computing

In recent years approximate computing has been extensively explored as a paradigm to design hardware and software solutions that save energy by trading off on the quality of the computed results. In applications that involve numerical computations with wide dynamic range, precision tuning of floating-point (FP) variables is a key knob to leverage the energy/quality trade-off of program results. This aspect assumes maximum relevance in the transprecision computing scenario, where accuracy of data is tuned at fine grain in application code. Performing precision tuning at fine grain requires a software development flow that streamlines the assessment of which variables have “precision slack” within an application. In this paper we introduce FlexFloat, an open-source software library that has been expressly designed to aid the development of transprecision applications. FlexFloat provides a C/C++ interface for supporting multiple FP formats. Unlike alternative libraries, FlexFloat enables to control the bit-width of mantissa and exponent fields and provides advanced features for the collection of runtime statistics, reducing the FP emulation time compared to the state-of-the-art solutions. Its design allows to emulate the behavior of standard IEEE FP types and custom extensions for reduced-precision computation. This makes the library suitable for adoption in multiple contexts, from manual exploration to integration into automatic tools. Experimental findings demonstrate that our approach can be used to perform a complete precision analysis from which deriving multiple program versions depending on the energy/quality trade-off. Furthermore, we show that the adoption of our methodology can lead to a significant reduction of energy consumption even on current commercial hardware (an embedded GPGPU).