FixedPoint number support for chisel3 (#328)

* FixedPoint number support for chisel3
FixedPoint numbers have a width and a binary position
Either, neither or both maybe inferred.
Firrtl will convert these to SInts during lowering passes

* Fixes based on Jack's comments on PR #328

* Add experimental warning to FixedPoint class and object

* Fixed comment per Adam's comment on PR #328

2 files changed, 47 insertions, 0 deletions

diff --git a/src/main/scala/chisel3/package.scala b/src/main/scala/chisel3/package.scala
index d0808980..e0364868 100644
--- a/src/main/scala/chisel3/package.scala
+++ b/src/main/scala/chisel3/package.scala
@@ -37,6 +37,8 @@ package object chisel3 {    // scalastyle:ignore package.object.name
   val UInt = chisel3.core.UInt
   type SInt = chisel3.core.SInt
   val SInt = chisel3.core.SInt
+  type FixedPoint = chisel3.core.FixedPoint
+  val FixedPoint = chisel3.core.FixedPoint
   type Bool = chisel3.core.Bool
   val Bool = chisel3.core.Bool
   val Mux = chisel3.core.Mux
@@ -150,6 +152,10 @@ package object chisel3 {    // scalastyle:ignore package.object.name
     def B: Bool = Bool(x)    // scalastyle:ignore method.name
   }
 
+  implicit class fromDoubleToLiteral(val x: Double) extends AnyVal {
+    def F(binaryPoint: Int): FixedPoint = FixedPoint.fromDouble(x, binaryPoint = binaryPoint)
+  }
+
   implicit class fromUIntToBitPatComparable(val x: UInt) extends AnyVal {
     final def === (that: BitPat): Bool = macro SourceInfoTransform.thatArg
     @deprecated("Use '=/=', which avoids potential precedence problems", "chisel3")
diff --git a/src/test/scala/chiselTests/FixedPointSpec.scala b/src/test/scala/chiselTests/FixedPointSpec.scala
new file mode 100644
index 00000000..69015e42
--- /dev/null
+++ b/src/test/scala/chiselTests/FixedPointSpec.scala
@@ -0,0 +1,41 @@
+// See LICENSE for license details.
+
+package chiselTests
+
+import chisel3._
+import chisel3.testers.BasicTester
+import org.scalatest._
+
+//scalastyle:off magic.number
+class FixedPointSpec extends FlatSpec with Matchers {
+  behavior of "fixed point utilities"
+
+  they should "allow conversion between doubles and the bigints needed to represent them" in {
+    val initialDouble = 0.125
+    val bigInt = FixedPoint.toBigInt(initialDouble, 4)
+    val finalDouble = FixedPoint.toDouble(bigInt, 4)
+
+    initialDouble should be(finalDouble)
+  }
+}
+
+class SBP extends Module {
+  val io = IO(new Bundle {
+    val in =  Input(FixedPoint(6, 2))
+    val out = Output(FixedPoint(4, 0))
+  })
+  io.out := io.in.setBinaryPoint(0)
+}
+class SBPTester extends BasicTester {
+  val dut = Module(new SBP)
+  dut.io.in := FixedPoint.fromDouble(3.75, binaryPoint = 2)
+
+  assert(dut.io.out === FixedPoint.fromDouble(3.0, binaryPoint = 0))
+
+  stop()
+}
+class SBPSpec extends ChiselPropSpec {
+  property("should allow set binary point") {
+    assertTesterPasses { new SBPTester }
+  }
+}