Dynamic Precision Numerics Using a Variable-Precision UNUM Type I HW Coprocessor

A very large internal accumulation register has been proposed to increase the accuracy of scientific code. However, there is a general class of iterative kernels where a vector of high-precision data must be saved from one iteration to the next. Saving the large internal accumulator to memory is impractical in such cases. This work proposes a Variable Precision (VP) Floating Point (FP) arithmetic co-processor architecture based on RISC-V, which 1/ supports legacy IEEE formats for input and output variables, 2/ uses variable length internal registers (up to 512 bits of mantissa) for inner loop multiply-add and 3/ supports loads and stores of intermediate results to cache memory with a dynamically adjustable precision (up to 256 bits of mantissa). It exploits the UNUM type I floating point format, proposing solutions to address some of its pitfalls such as the variable latency of the internal operation, and the variable memory footprint of the intermediate variables. This work is integrated on FPGA and demonstrated on a representative example.