util: add GrayCode (#2353) (#2354)

(cherry picked from commit 91d7baa8e7162d736f46b6d4964b09016d2dd172)

Co-authored-by: Kevin Laeufer <laeufer@cs.berkeley.edu>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/main/scala/chisel3/util/GrayCode.scala b/src/main/scala/chisel3/util/GrayCode.scala
new file mode 100644
index 00000000..ef310ee9
--- /dev/null
+++ b/src/main/scala/chisel3/util/GrayCode.scala
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package chisel3.util
+
+import chisel3._
+
+object BinaryToGray {
+
+  /** Turns a binary number into gray code. */
+  def apply(in: UInt): UInt = in ^ (in >> 1)
+}
+
+object GrayToBinary {
+
+  /** Inverts the [[BinaryToGray]] operation. */
+  def apply(in: UInt, width: Int): UInt = apply(in(width - 1, 0))
+
+  /** Inverts the [[BinaryToGray]] operation. */
+  def apply(in: UInt): UInt = if (in.getWidth < 2) { in }
+  else {
+    val bits = in.getWidth - 2 to 0 by -1
+    Cat(bits.scanLeft(in.head(1)) { case (prev, ii) => prev ^ in(ii) })
+  }
+}