Make TruthTable accept unknown input width (#2387) (#2417)

Widths are now padded to the maximum width of the inputs.

Co-authored-by: Jack Koenig <koenig@sifive.com>
(cherry picked from commit 546b4e13fe90ff09d24b63664c072d46c13c0c38)

Co-authored-by: Jiuyang Liu <liu@jiuyang.me>

2 files changed, 31 insertions, 2 deletions

diff --git a/src/main/scala/chisel3/util/experimental/decode/TruthTable.scala b/src/main/scala/chisel3/util/experimental/decode/TruthTable.scala
index e742fd66..00fa0f9c 100644
--- a/src/main/scala/chisel3/util/experimental/decode/TruthTable.scala
+++ b/src/main/scala/chisel3/util/experimental/decode/TruthTable.scala
@@ -31,10 +31,15 @@ object TruthTable {
 
   /** Convert a table and default output into a [[TruthTable]]. */
   def apply(table: Iterable[(BitPat, BitPat)], default: BitPat, sort: Boolean = true): TruthTable = {
-    require(table.map(_._1.getWidth).toSet.size == 1, "input width not equal.")
+    val inputWidth = table.map(_._1.getWidth).max
     require(table.map(_._2.getWidth).toSet.size == 1, "output width not equal.")
     val outputWidth = table.map(_._2.getWidth).head
-    val mergedTable = table
+    val mergedTable = table.map {
+      // pad input signals if necessary
+      case (in, out) if inputWidth > in.width =>
+        (BitPat.N(inputWidth - in.width) ## in, out)
+      case (in, out) => (in, out)
+    }
       .groupBy(_._1.toString)
       .map {
         case (key, values) =>
diff --git a/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala b/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala
index 2ef316bb..fa2c6f08 100644
--- a/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala
+++ b/src/test/scala/chiselTests/util/experimental/TruthTableSpec.scala
@@ -80,4 +80,28 @@ class TruthTableSpec extends AnyFlatSpec {
     }
     assert(chisel3.stage.ChiselStage.emitChirrtl(new Foo) == chisel3.stage.ChiselStage.emitChirrtl(new Foo))
   }
+  "TruthTable" should "accept unknown input width" in {
+    val t = TruthTable(
+      Seq(
+        BitPat(0.U) -> BitPat.dontCare(1),
+        BitPat(1.U) -> BitPat.dontCare(1),
+        BitPat(2.U) -> BitPat.dontCare(1),
+        BitPat(3.U) -> BitPat.dontCare(1),
+        BitPat(4.U) -> BitPat.dontCare(1),
+        BitPat(5.U) -> BitPat.dontCare(1),
+        BitPat(6.U) -> BitPat.dontCare(1),
+        BitPat(7.U) -> BitPat.dontCare(1)
+      ),
+      BitPat.N(1)
+    )
+    assert(t.toString contains "000->?")
+    assert(t.toString contains "001->?")
+    assert(t.toString contains "010->?")
+    assert(t.toString contains "011->?")
+    assert(t.toString contains "100->?")
+    assert(t.toString contains "101->?")
+    assert(t.toString contains "110->?")
+    assert(t.toString contains "111->?")
+    assert(t.toString contains "     0")
+  }
 }