GCD.scala

#!/usr/bin/env amm

import $ivy.`edu.berkeley.cs::chisel3:3.4.+`, chisel3._

class GCDIO extends Bundle {
  val value1        = Input(UInt(16.W))
  val value2        = Input(UInt(16.W))
  val loadingValues = Input(Bool())
  val outputGCD     = Output(UInt(16.W))
  val outputValid   = Output(Bool())
}

/**
  * Compute GCD using subtraction method.
  * Subtracts the smaller from the larger until register y is zero.
  * value in register x is then the GCD
  */
class GCD extends Module {
  // This is an artefact of ammonite's REPL de-conflicting class names
  override def desiredName = "GCD"
  val io = IO(new GCDIO)

  val x  = Reg(UInt())
  val y  = Reg(UInt())

  when(x > y) { x := x - y }
    .otherwise { y := y - x }

  when(io.loadingValues) {
    x := io.value1
    y := io.value2
  }

  io.outputGCD := x
  io.outputValid := y === 0.U
}

@main
def main(args: String*) = chisel3.Driver.execute(args.toArray, () => new GCD)