Add messages to require statements in Math (#3385)

* log2 functions
* unsignedBitLength

(cherry picked from commit 88fecfc)

# Conflicts:
#	src/main/scala/chisel3/util/Math.scala

src/main/scala/chisel3/util/Math.scala

@@ -27,7 +27,15 @@ object log2Up {
   // https://github.com/freechipsproject/chisel3/issues/847
   //@chiselRuntimeDeprecated
   //@deprecated("Use log2Ceil instead", "chisel3")
+<<<<<<< HEAD
   def apply(in: BigInt): Int = Chisel.log2Up(in)
+=======
+  def apply(in: BigInt): Int = {
+    require(in >= 0, s"log2Up is only defined on integers >= 0, got $in")
+    1.max((in - 1).bitLength)
+  }
+  def apply(in: Int): Int = apply(BigInt(in))
+>>>>>>> 88fecfc1c (Add messages to require statements in Math (#3385))
 }
 
 /** Compute the log2 of a Scala integer, rounded up.
@@ -46,7 +54,7 @@ object log2Up {
   */
 object log2Ceil {
   def apply(in: BigInt): Int = {
-    require(in > 0)
+    require(in > 0, s"log2 is only defined on integers > 0, got $in")
     (in - 1).bitLength
   }
   def apply(in: Int): Int = apply(BigInt(in))
@@ -109,7 +117,7 @@ object unsignedBitLength {
     * @return - an Int representing the number of bits to encode.
     */
   def apply(in: BigInt): Int = {
-    require(in >= 0)
+    require(in >= 0, s"Unsigned integers must be non-negative, got $in")
     in.bitLength
   }
 }