Updated Bag of Tricks (markdown)

Bag-of-Tricks.md

@@ -247,6 +247,49 @@ root.printTo(chunkPrint);
 
 See issue [#206](https://github.com/bblanchon/ArduinoJson/issues/206).
 
+## Compute hash of JSON output
+
+Here is how you can compute the CRC32 hash of the JSON output without consuming a lot of memory.
+
+This can be very handy to compare two JSON trees.
+
+```c++
+#include <FastCRC.h> // https://github.com/FrankBoesing/FastCRC
+
+class HashPrint : public Print {
+public:
+    HashPrint()
+    {
+        _hash = _hasher.crc32(NULL, 0);
+    }
+
+    virtual size_t write(uint8_t c)
+    {
+        _hash = _hasher.crc32_upd(&c, 1);
+    }
+
+    uint32_t hash() const
+    {
+        return _hash;
+    }
+
+private:
+    FastCRC32 _hasher;
+    uint32_t _hash;
+};
+```
+
+To use this in your code:
+
+```c++
+HashPrint hashPrint;
+root.printTo(hashPrint);
+Serial.println(hashPrint.hash());
+```
+
+See issue [#390](https://github.com/bblanchon/ArduinoJson/issues/390).
+
+
 ## Throw exception when JsonBuffer is too small
 
 Here is a static decorator that will behave as the decorated `JsonBuffer`, except that it will throw an exception if the allocation fails: