SkTDynamicHash: support remove() without needing Deleted().

src/core/SkTDynamicHash.h

Index: src/core/SkTDynamicHash.h
diff --git a/src/core/SkTDynamicHash.h b/src/core/SkTDynamicHash.h
index 21aca07b907174d3d7e3071e64b0b7857be60aa5..e7b57edfa62d7359414ecc50a0e01fc045c3c472 100644
--- a/src/core/SkTDynamicHash.h
+++ b/src/core/SkTDynamicHash.h
@@ -34,10 +34,9 @@ public:
         int index = this->firstIndex(key);
         for (int round = 0; round < fCapacity; round++) {
             T* candidate = fArray[index];
-            if (candidate == Empty()) {
+            if (candidate == NULL) {

[reed1, 2013/08/07 18:10:32]

nit: NULL == candidate

                 return NULL;
-            }
-            if (candidate != Deleted() && Equal(*candidate, key)) {
+            } else if(Equal(*candidate, key)) {
                 return candidate;
             }
             index = this->nextIndex(index, round);
@@ -54,12 +53,11 @@ public:
         int index = this->firstIndex(key);
         for (int round = 0; round < fCapacity; round++) {
             T* candidate = fArray[index];
-            if (candidate == Empty() || candidate == Deleted()) {
+            if (candidate == NULL) {

[reed1, 2013/08/07 18:10:32]

see prev. nit

                 fArray[index] = newEntry;
                 fCount++;
                 return;
-            }
-            if (Equal(*candidate, key)) {
+            } else if (Equal(*candidate, key)) {
                 fArray[index] = newEntry;
                 return;
             }
@@ -84,7 +82,7 @@ protected:
         int index = this->firstIndex(key);
         for (int round = 0; round < fCapacity; round++) {
             const T* candidate = fArray[index];
-            if (candidate == Empty() || candidate == Deleted() || Equal(*candidate, key)) {
+            if (candidate == NULL || Equal(*candidate, key)) {

[reed1, 2013/08/07 18:10:32]

again with the nits

                 return round;
             }
             index = this->nextIndex(index, round);
@@ -94,13 +92,9 @@ protected:
     }
 
 private:
-    // We have two special values to indicate an empty or deleted entry.
-    static const T* Empty()   { return reinterpret_cast<const T*>(0); }  // i.e. NULL
-    static const T* Deleted() { return reinterpret_cast<const T*>(1); }  // Also an invalid pointer.
-
     static T** AllocArray(int capacity) {
         T** array = (T**)sk_malloc_throw(sizeof(T*) * capacity);
-        sk_bzero(array, sizeof(T*) * capacity);  // All cells == Empty().
+        sk_bzero(array, sizeof(T*) * capacity);  // All cells == NULL.
         return array;
     }
 
@@ -108,11 +102,20 @@ private:
         int index = this->firstIndex(key);
         for (int round = 0; round < fCapacity; round++) {
             const T* candidate = fArray[index];
-            if (candidate == Empty()) {
+            if (candidate == NULL) {

[reed1, 2013/08/07 18:10:32]

not again?

                 return;
-            }
-            if (candidate != Deleted() && Equal(*candidate, key)) {
-                fArray[index] = const_cast<T*>(Deleted());
+            } else if (Equal(*candidate, key)) {
+                // To delete an entry we find the last non-empty entry in this collision chain, move
+                // it up here, then clear out that last entry.  This way there's never an empty slot
+                // in the middle of a collision chain.
+                int last = index;
+                while (fArray[nextIndex(last, round)] != NULL) {
+                    last = nextIndex(last, round);
+                    round++;
+                }
+                // Note how this works even if index == last.
+                fArray[index] = fArray[last];
+                fArray[last] = NULL;
                 fCount--;
                 return;
             }
@@ -136,7 +139,7 @@ private:
 
         for (int i = 0; i < oldCapacity; i++) {
             T* entry = oldArray[i];
-            if (entry != Empty() && entry != Deleted()) {
+            if (entry != NULL) {
                 this->add(entry);
             }
         }
@@ -162,7 +165,7 @@ private:
         return (index + round + 1) & this->hashMask();
     }
 
-    int fCount;     // Number of non-empty, non-deleted entries in fArray.
+    int fCount;     // Number of non-NULL entries in fArray.
     int fCapacity;  // Number of entries in fArray.  Always a power of 2.
     T** fArray;
 };