Fixed UIntToOH(x, 1) invocation with x.width == 0 (#778)

2 files changed, 15 insertions, 2 deletions

diff --git a/src/main/scala/chisel3/util/OneHot.scala b/src/main/scala/chisel3/util/OneHot.scala
index 8a0bb9fc..a6af0d99 100644
--- a/src/main/scala/chisel3/util/OneHot.scala
+++ b/src/main/scala/chisel3/util/OneHot.scala
@@ -45,9 +45,10 @@ object UIntToOH {
   def apply(in: UInt): UInt = 1.U << in
   def apply(in: UInt, width: Int): UInt = width match {
     case 0 => 0.U(0.W)
+    case 1 => 1.U(1.W)
     case _ =>
       val shiftAmountWidth = log2Ceil(width)
-      val shiftAmount = in.pad(shiftAmountWidth)((shiftAmountWidth - 1) max 0, 0)
+      val shiftAmount = in.pad(shiftAmountWidth)(shiftAmountWidth - 1, 0)
       (1.U << shiftAmount)(width - 1, 0)
   }
 }
diff --git a/src/test/scala/chiselTests/OneHotMuxSpec.scala b/src/test/scala/chiselTests/OneHotMuxSpec.scala
index e12d7913..be252bef 100644
--- a/src/test/scala/chiselTests/OneHotMuxSpec.scala
+++ b/src/test/scala/chiselTests/OneHotMuxSpec.scala
@@ -43,6 +43,14 @@ class OneHotMuxSpec extends FreeSpec with Matchers with ChiselRunners {
   "UIntToOH with output width greater than 2^(input width)" in {
     assertTesterPasses(new UIntToOHTester)
   }
+  "UIntToOH should not accept width of zero (until zero-width wires are fixed" in {
+    intercept[java.lang.IllegalArgumentException] {
+      assertTesterPasses(new BasicTester {
+        val out = UIntToOH(0.U, 0)
+      })
+    }
+  }
+
 }
 
 class SimpleOneHotTester extends BasicTester {
@@ -288,9 +296,13 @@ class DifferentBundleOneHotTester extends BasicTester {
 
 class UIntToOHTester extends BasicTester {
   val out = UIntToOH(1.U, 3)
-
   require(out.getWidth == 3)
   assert(out === 2.U)
 
+  val out2 = UIntToOH(0.U, 1)
+  require(out2.getWidth == 1)
+  assert(out2 === 1.U)
+
   stop()
 }
+