I haven’t studied that module but I am going to go out on a limb here to try and give you an insight, and I can state the general principle that the hardware description is a shallow embedding within the Scala/Chisel framework and so, unlike system verilog, you will not find lines of Scala which directly represent the corresponding floating point operations. What you will find is a higher order framework of functions and objects which, when compiled and executed, causes the FPU unit to be generated, and subsequently dumped as Verilog code. Hence, you will find a formal separation between abstract blocks of declarative code (stating what should be done) and imperative code (stating, step by step, how something should be done). So we end up with a system which is powerful but hard to understand, at least for outsiders. So without simplifying too much, I’m guessing that the hardfloat code base contains the what code and FPU.scala contains the how code which instantiates the FPU within the Rocket processor. Of course there is nothing within the Chisel framework or the Scala language that enforces a clean separation between different programming styles or intents. I’m sure when you’ve studied the code for a while you will realise the shortcomings of my hand waving explanation. Sent from my iPhone