Merge pull request #1033 from freechipsproject/popcount

Tighten inferred width for PopCount

1 files changed, 27 insertions, 0 deletions

diff --git a/src/test/scala/chiselTests/PopCount.scala b/src/test/scala/chiselTests/PopCount.scala
new file mode 100644
index 00000000..d9b3b837
--- /dev/null
+++ b/src/test/scala/chiselTests/PopCount.scala
@@ -0,0 +1,27 @@
+// See LICENSE for license details.
+
+package chiselTests
+
+import chisel3._
+import chisel3.util.PopCount
+import org.scalatest._
+import org.scalatest.prop._
+import chisel3.testers.BasicTester
+
+class PopCountTester(n: Int) extends BasicTester {
+  val x = RegInit(0.U(n.W))
+  x := x + 1.U
+  when (RegNext(x === ~0.U(n.W))) { stop() }
+
+  val result = PopCount(x.asBools)
+  val expected = x.asBools.foldLeft(0.U)(_ +& _)
+  assert(result === expected)
+
+  require(result.getWidth == BigInt(n).bitLength)
+}
+
+class PopCountSpec extends ChiselPropSpec {
+  property("Mul lookup table should return the correct result") {
+    forAll(smallPosInts) { (n: Int) =>  assertTesterPasses { new PopCountTester(n) } }
+  }
+}