chisel3 arithmetic operations on Doubles

Question

Please I have problems manipulating arithmetic operations with doubles in chisel. I have been seeing examples that uses just the following types: Int,UInt,SInt. I saw here that arithmetic operations where described only for SInt and UInt. What about Double? I tried to declare my output out as Double, but didn't know how. Because the output of my code is Double. Is there a way to declare in Bundle an input and an output of type Double?

Here is my code:

class hashfunc(val k:Int, val n: Int ) extends Module {

  val a = k + k
  val io = IO(new Bundle {
    val b=Input(UInt(k.W))
    val w=Input(UInt(k.W))
    var out  = Output(UInt(a.W))
  })

   val tabHash1 = new Array[Array[Double]](n)
    val x   = new ArrayBuffer[(Double, Data)]
    val tabHash = new Array[Double](tabHash1.size)
  for (ind <- tabHash1.indices){
     var sum=0.0
    for (ind2 <- 0 until x.size){
      sum += ( x(ind2) * tabHash1(ind)(ind2) )
   }     
      tabHash(ind) = ((sum + io.b) / io.w)
    }
  io.out := tabHash.reduce(_ + _)
 }

When I compile the code, I get the following error: code error

Thank you for your kind attention, looking forward to your responses.

Actually it is because my aim is to generate the verilog version of this code. And I think the way I write the code, will determine how good the verilog generated will be. So someone could verify if I used the hardware property of chisel correctly. — Foutse
Did you mean synthesizable verilog? It is very difficult to generate a synthesizable verilog from a free-style programming language. It is high-level synthesis. I suggest you write verilog manually instead and forget about this. — Serge

Brian Magnuson Brian Magnuson · Accepted Answer · 2017-08-24T14:35:20

Operations on floating point numbers (Double in this case) are not supported directly by any HDL. The reason for this is that while addition/subtraction/multiplication of fixed point numbers is well defined there are a lot of design space trade-offs for floating point hardware as it is a much more complex piece of hardware.

That is to say, a high performance floating point unit is a significant piece of hardware in it's own right and would be time shared in any realistic design.

chisel3 arithmetic operations on Doubles

2 Answers