Reject log2Up on negative inputs

Mathematically, we should also reject 0, like log2Ceil does.  But accepting
0 and returning 1 is more in the spirit of the special case for widths.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/main/scala/Chisel/util/Math.scala b/src/main/scala/Chisel/util/Math.scala
index 270301f0..5f8212d8 100644
--- a/src/main/scala/Chisel/util/Math.scala
+++ b/src/main/scala/Chisel/util/Math.scala
@@ -7,7 +7,10 @@ package Chisel
 
 /** Compute the log2 rounded up with min value of 1 */
 object log2Up {
-  def apply(in: BigInt): Int = 1 max (in-1).bitLength
+  def apply(in: BigInt): Int = {
+    require(in >= 0)
+    1 max (in-1).bitLength
+  }
   def apply(in: Int): Int = apply(BigInt(in))
 }