--- jsr166/src/main/java/util/ArrayDeque.java	2016/11/13 02:10:09	1.113
+++ jsr166/src/main/java/util/ArrayDeque.java	2016/11/20 08:30:56	1.119
@@ -68,13 +68,15 @@ public class ArrayDeque<E> extends Abstr
      *
      * Because in a circular array, elements are in general stored in
      * two disjoint such slices, we help the VM by writing unusual
-     * nested loops for all traversals over the elements.
+     * nested loops for all traversals over the elements.  Having only
+     * one hot inner loop body instead of two or three eases human
+     * maintenance and encourages VM loop inlining into the caller.
      */
 
     /**
      * The array in which the elements of the deque are stored.
-     * We guarantee that all array cells not holding deque elements
-     * are always null.
+     * All array cells not holding deque elements are always null.
+     * The array always has at least one null slot (at tail).
      */
     transient Object[] elements;
 
@@ -88,7 +90,8 @@ public class ArrayDeque<E> extends Abstr
 
     /**
      * The index at which the next element would be added to the tail
-     * of the deque (via addLast(E), add(E), or push(E)).
+     * of the deque (via addLast(E), add(E), or push(E));
+     * elements[tail] is always null.
      */
     transient int tail;
 
@@ -187,7 +190,10 @@ public class ArrayDeque<E> extends Abstr
      * @param numElements lower bound on initial capacity of the deque
      */
     public ArrayDeque(int numElements) {
-        elements = new Object[Math.max(1, numElements + 1)];
+        elements =
+            new Object[(numElements < 1) ? 1 :
+                       (numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
+                       numElements + 1];
     }
 
     /**
@@ -201,7 +207,7 @@ public class ArrayDeque<E> extends Abstr
      * @throws NullPointerException if the specified collection is null
      */
     public ArrayDeque(Collection<? extends E> c) {
-        elements = new Object[c.size() + 1];
+        this(c.size());
         addAll(c);
     }
 
@@ -224,19 +230,21 @@ public class ArrayDeque<E> extends Abstr
     }
 
     /**
-     * Adds i and j, mod modulus.
-     * Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
+     * Circularly adds the given distance to index i, mod modulus.
+     * Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
+     * @return index 0 <= i < modulus
      */
-    static final int add(int i, int j, int modulus) {
-        if ((i += j) - modulus >= 0) i -= modulus;
+    static final int add(int i, int distance, int modulus) {
+        if ((i += distance) - modulus >= 0) distance -= modulus;
         return i;
     }
 
     /**
      * Subtracts j from i, mod modulus.
-     * Index i must be logically ahead of j.
-     * Returns the "circular distance" from j to i.
-     * Precondition and postcondition: 0 <= i < modulus, 0 <= j < modulus.
+     * Index i must be logically ahead of index j.
+     * Precondition: 0 <= i < modulus, 0 <= j < modulus.
+     * @return the "circular distance" from j to i; corner case i == j
+     * is diambiguated to "empty", returning 0.
      */
     static final int sub(int i, int j, int modulus) {
         if ((i -= j) < 0) i += modulus;
@@ -314,10 +322,10 @@ public class ArrayDeque<E> extends Abstr
      *         of its elements are null
      */
     public boolean addAll(Collection<? extends E> c) {
-        final int s = size(), needed;
-        if ((needed = s + c.size() - elements.length + 1) > 0)
+        final int s, needed;
+        if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
             grow(needed);
-        c.forEach(e -> addLast(e));
+        c.forEach(this::addLast);
         // checkInvariants();
         return size() > s;
     }
@@ -608,10 +616,11 @@ public class ArrayDeque<E> extends Abstr
         // checkInvariants();
         final Object[] es = elements;
         final int capacity = es.length;
-        final int h = head;
+        final int h, t;
         // number of elements before to-be-deleted elt
-        final int front = sub(i, h, capacity);
-        final int back = size() - front - 1; // number of elements after
+        final int front = sub(i, h = head, capacity);
+        // number of elements after to-be-deleted elt
+        final int back = sub(t = tail, i, capacity) - 1;
         if (front < back) {
             // move front elements forwards
             if (h <= i) {
@@ -627,14 +636,13 @@ public class ArrayDeque<E> extends Abstr
             return false;
         } else {
             // move back elements backwards
-            tail = dec(tail, capacity);
+            tail = dec(t, capacity);
             if (i <= tail) {
                 System.arraycopy(es, i + 1, es, i, back);
             } else { // Wrap around
-                int firstLeg = capacity - (i + 1);
-                System.arraycopy(es, i + 1, es, i, firstLeg);
+                System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
                 es[capacity - 1] = es[0];
-                System.arraycopy(es, 1, es, 0, back - firstLeg - 1);
+                System.arraycopy(es, 1, es, 0, t - 1);
             }
             es[tail] = null;
             // checkInvariants();
@@ -858,13 +866,12 @@ public class ArrayDeque<E> extends Abstr
         public boolean tryAdvance(Consumer<? super E> action) {
             if (action == null)
                 throw new NullPointerException();
-            int t, i;
-            if ((t = fence) < 0) t = getFence();
-            if (t == (i = cursor))
+            final int t, i;
+            if ((t = getFence()) == (i = cursor))
                 return false;
-            final Object[] es;
-            action.accept(nonNullElementAt(es = elements, i));
+            final Object[] es = elements;
             cursor = inc(i, es.length);
+            action.accept(nonNullElementAt(es, i));
             return true;
         }
 
@@ -1097,17 +1104,16 @@ public class ArrayDeque<E> extends Abstr
     private <T> T[] toArray(Class<T[]> klazz) {
         final Object[] es = elements;
         final T[] a;
-        final int size = size(), head = this.head, end;
-        final int len = Math.min(size, es.length - head);
-        if ((end = head + size) >= 0) {
+        final int head = this.head, tail = this.tail, end;
+        if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
             a = Arrays.copyOfRange(es, head, end, klazz);
         } else {
             // integer overflow!
-            a = Arrays.copyOfRange(es, 0, size, klazz);
-            System.arraycopy(es, head, a, 0, len);
+            a = Arrays.copyOfRange(es, 0, end - head, klazz);
+            System.arraycopy(es, head, a, 0, es.length - head);
         }
-        if (tail < head)
-            System.arraycopy(es, 0, a, len, tail);
+        if (end != tail)
+            System.arraycopy(es, 0, a, es.length - head, tail);
         return a;
     }
 
@@ -1232,6 +1238,8 @@ public class ArrayDeque<E> extends Abstr
 
     /** debugging */
     void checkInvariants() {
+        // Use head and tail fields with empty slot at tail strategy.
+        // head == tail disambiguates to "empty".
         try {
             int capacity = elements.length;
             // assert head >= 0 && head < capacity;