From 09ce36e79ba5a999d0e47ec482bbf06857cf7043 Mon Sep 17 00:00:00 2001
From: Andrew Waterman
Date: Thu, 14 Apr 2016 23:36:46 -0700
Subject: Disallow Counters with negative n

One could make an argument for disallowing n=0, too, but HW generators
will benefit from our leniency.

Closes #107.  Thanks @jackkoenig
---
 src/main/scala/Chisel/util/Counter.scala | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

(limited to 'src/main')

diff --git a/src/main/scala/Chisel/util/Counter.scala b/src/main/scala/Chisel/util/Counter.scala
index 14f51ec4..3a9db309 100644
--- a/src/main/scala/Chisel/util/Counter.scala
+++ b/src/main/scala/Chisel/util/Counter.scala
@@ -7,20 +7,21 @@ package Chisel
   * maximum output value of the counter), need not be a power of two
   */
 class Counter(val n: Int) {
-  val value = if (n == 1) UInt(0) else Reg(init=UInt(0, log2Up(n)))
+  require(n >= 0)
+  val value = if (n > 1) Reg(init=UInt(0, log2Up(n))) else UInt(0)
   /** Increment the counter, returning whether the counter currently is at the
     * maximum and will wrap. The incremented value is registered and will be
     * visible on the next cycle.
     */
   def inc(): Bool = {
-    if (n == 1) {
-      Bool(true)
-    } else {
+    if (n > 1) {
       val wrap = value === UInt(n-1)
       value := value + UInt(1)
       if (!isPow2(n))
         when (wrap) { value := UInt(0) }
       wrap
+    } else {
+      Bool(true)
     }
   }
 }
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