[libre-riscv-dev] IEEE754 FPU

[Luke Kenneth Casson Leighton]

this is the original that attie converted from:
https://github.com/m-labs/milkymist/blob/master/cores/pfpu/rtl/pfpu_faddsub.v

result:
https://github.com/nakengelhardt/fpgagraphlib/blob/master/src/faddsub.py