Add optimized CSizeComputer serializers

random-zebra · random-zebra · commit 9b801d0b9fa2 · 2020-05-27T12:03:09.000+02:00
To get the advantages of faster GetSerializeSize() implementations back that were removed in "Make GetSerializeSize a wrapper on top of CSizeComputer", reintroduce them in the few places in the form of a specialized Serialize() implementation. This actually gets us in a better state than before, as these even get used when they're invoked indirectly in the serialization of another object. backports bitcoin/bitcoin@25a211a
diff --git a/src/serialize.h b/src/serialize.h
@@ -155,6 +155,8 @@ inline float ser_uint32_to_float(uint32_t y)
 // i.e. anything that supports .read(char*, size_t) and .write(char*, size_t)
 //
 
+class CSizeComputer;
+
 enum {
     // primary actions
     SER_NETWORK = (1 << 0),
@@ -278,6 +280,8 @@ inline unsigned int GetSizeOfCompactSize(uint64_t nSize)
         return sizeof(unsigned char) + sizeof(uint64_t);
 }
 
+inline void WriteCompactSize(CSizeComputer& os, uint64_t nSize);
+
 template <typename Stream>
 void WriteCompactSize(Stream& os, uint64_t nSize)
 {
@@ -358,6 +362,9 @@ inline unsigned int GetSizeOfVarInt(I n)
     return nRet;
 }
 
+template<typename I>
+inline void WriteVarInt(CSizeComputer& os, I n);
+
 template <typename Stream, typename I>
 void WriteVarInt(Stream& os, I n)
 {
@@ -825,6 +832,18 @@ inline void SerReadWrite(Stream& s, T& obj, CSerActionUnserialize ser_action)
 }
 
 
+
+/* ::GetSerializeSize implementations
+ *
+ * Computing the serialized size of objects is done through a special stream
+ * object of type CSizeComputer, which only records the number of bytes written
+ * to it.
+ *
+ * If your Serialize or SerializationOp method has non-trivial overhead for
+ * serialization, it may be worthwhile to implement a specialized version for
+ * CSizeComputer, which uses the s.seek() method to record bytes that would
+ * be written instead.
+ */
 class CSizeComputer
 {
 protected:
@@ -863,6 +882,17 @@ class CSizeComputer
     int GetType() const { return nType; }
 };
 
+template<typename I>
+inline void WriteVarInt(CSizeComputer &s, I n)
+{
+    s.seek(GetSizeOfVarInt<I>(n));
+}
+
+inline void WriteCompactSize(CSizeComputer &s, uint64_t nSize)
+{
+    s.seek(GetSizeOfCompactSize(nSize));
+}
+
 template <typename T>
 size_t GetSerializeSize(const T& t, int nType, int nVersion = 0)
 {
