Added string deduplication (closes #1303)

src/ArduinoJson/Memory/MemoryPool.hpp

@@ -51,40 +51,43 @@ class MemoryPool {
     return allocRight<VariantSlot>();
   }
 
-  char* allocFrozenString(size_t n) {
-    if (!canAlloc(n))
-      return 0;
-    char* s = _left;
-    _left += n;
-    checkInvariants();
-    return s;
-  }
-
   template <typename TAdaptedString>
-  char* saveString(const TAdaptedString& str) {
+  const char* saveString(const TAdaptedString& str) {
     if (str.isNull())
       return 0;
+
+#if ARDUINOJSON_ENABLE_STRING_DEDUPLICATION
+    const char* existingCopy = findString(str.begin());
+    if (existingCopy)
+      return existingCopy;
+#endif
+
     size_t n = str.size();
-    char* dup = allocFrozenString(n + 1);
-    if (dup) {
-      str.copyTo(dup, n);
-      dup[n] = 0;  // force null-terminator
+
+    char* newCopy = allocString(n + 1);
+    if (newCopy) {
+      str.copyTo(newCopy, n);
+      newCopy[n] = 0;  // force null-terminator
     }
-    return dup;
+    return newCopy;
   }
 
-  StringSlot allocExpandableString() {
-    StringSlot s;
-    s.value = _left;
-    s.size = size_t(_right - _left);
-    checkInvariants();
-    return s;
+  void getFreeZone(char** zoneStart, size_t* zoneSize) const {
+    *zoneStart = _left;
+    *zoneSize = size_t(_right - _left);
   }
 
-  void freezeString(StringSlot& s, size_t newSize) {
-    _left = (s.value + newSize);
-    s.size = newSize;
+  const char* saveStringFromFreeZone(size_t len) {
+#if ARDUINOJSON_ENABLE_STRING_DEDUPLICATION
+    const char* dup = findString(_left);
+    if (dup)
+      return dup;
+#endif
+
+    const char* str = _left;
+    _left += len;
     checkInvariants();
+    return str;
   }
 
   void clear() {
@@ -100,18 +103,6 @@ class MemoryPool {
     return _begin <= p && p < _end;
   }
 
-  template <typename T>
-  T* allocRight() {
-    return reinterpret_cast<T*>(allocRight(sizeof(T)));
-  }
-
-  void* allocRight(size_t bytes) {
-    if (!canAlloc(bytes))
-      return 0;
-    _right -= bytes;
-    return _right;
-  }
-
   // Workaround for missing placement new
   void* operator new(size_t, void* p) {
     return p;
@@ -163,6 +154,46 @@ class MemoryPool {
     ARDUINOJSON_ASSERT(isAligned(_right));
   }
 
+#if ARDUINOJSON_ENABLE_STRING_DEDUPLICATION
+  template <typename TIterator>
+  const char* findString(TIterator str) {
+    for (char* next = _begin; next < _left; ++next) {
+      char* begin = next;
+
+      // try to match
+      for (TIterator it = str; *it == *next; ++it) {
+        if (*next++ == 0)
+          return begin;
+      }
+
+      // jump to next terminator
+      while (*next) ++next;
+    }
+    return 0;
+  }
+#endif
+
+  char* allocString(size_t n) {
+    if (!canAlloc(n))
+      return 0;
+    char* s = _left;
+    _left += n;
+    checkInvariants();
+    return s;
+  }
+
+  template <typename T>
+  T* allocRight() {
+    return reinterpret_cast<T*>(allocRight(sizeof(T)));
+  }
+
+  void* allocRight(size_t bytes) {
+    if (!canAlloc(bytes))
+      return 0;
+    _right -= bytes;
+    return _right;
+  }
+
   char *_begin, *_left, *_right, *_end;
 };