Add DifferenceFormatter

Author: ryanofsky

src/blockencodings.h

@@ -25,6 +25,28 @@ struct TransactionCompressor {
     }
 };
 
+class DifferenceFormatter
+{
+    uint64_t m_shift = 0;
+
+public:
+    template<typename Stream, typename I>
+    void Ser(Stream& s, I v)
+    {
+        if (v < m_shift || v >= std::numeric_limits<uint64_t>::max()) throw std::ios_base::failure("differential value overflow");
+        WriteCompactSize(s, v - m_shift);
+        m_shift = uint64_t(v) + 1;
+    }
+    template<typename Stream, typename I>
+    void Unser(Stream& s, I& v)
+    {
+        uint64_t n = ReadCompactSize(s);
+        m_shift += n;
+        if (m_shift < n || m_shift >= std::numeric_limits<uint64_t>::max() || m_shift < std::numeric_limits<I>::min() || m_shift > std::numeric_limits<I>::max()) throw std::ios_base::failure("differential value overflow");
+        v = I(m_shift++);
+    }
+};
+
 class BlockTransactionsRequest {
 public:
     // A BlockTransactionsRequest message