  The posit representation for real numbers is an alternative to the ubiquitous
IEEE 754 floating-point standard. In this work, we present PERCIVAL, an
application-level posit capable RISC-V core based on CVA6 that can execute all
posit instructions, including the quire fused operations. This solves the
obstacle encountered by previous works, which only included partial posit
support or which had to emulate posits in software, thus limiting the scope or
the scalability of their applications. In addition, Xposit, a RISC-V extension
for posit instructions is incorporated into LLVM. Therefore, PERCIVAL is the
first work that integrates the complete posit instruction set in hardware.
These elements allow for the native execution of posit instructions as well as
the standard floating-point ones, further permitting the comparison of these
representations. FPGA and ASIC synthesis show the hardware cost of implementing
32-bit posits and highlight the significant overhead of including a quire
accumulator. However, results comparing posits and IEEE floats show that the
quire enables a more accurate execution of dot products. In general matrix
multiplications, the accuracy error is reduced up to 4 orders of magnitude when
compared with single-precision floats. Furthermore, performance comparisons
show that these accuracy improvements do not hinder their execution, as posits
run as fast as single-precision floats and exhibit better timing than
double-precision floats, thus potentially providing an alternative
representation.
