Add single sha256 call to CHashWriter

src/hash.h

@@ -98,7 +98,7 @@ inline uint160 Hash160(const T1& in1)
 class CHashWriter
 {
 private:
-    CHash256 ctx;
+    CSHA256 ctx;
 
     const int nType;
     const int nVersion;
@@ -110,13 +110,27 @@ public:
     int GetVersion() const { return nVersion; }
 
     void write(const char *pch, size_t size) {
-        ctx.Write({(const unsigned char*)pch, size});
+        ctx.Write((const unsigned char*)pch, size);
     }
 
-    // invalidates the object
+    /** Compute the double-SHA256 hash of all data written to this object.
+     *
+     * Invalidates this object.
+     */
     uint256 GetHash() {
         uint256 result;
-        ctx.Finalize(result);
+        ctx.Finalize(result.begin());
+        ctx.Reset().Write(result.begin(), CSHA256::OUTPUT_SIZE).Finalize(result.begin());
+        return result;
+    }
+
+    /** Compute the SHA256 hash of all data written to this object.
+     *
+     * Invalidates this object.
+     */
+    uint256 GetSHA256() {
+        uint256 result;
+        ctx.Finalize(result.begin());
         return result;
     }
 
@@ -124,9 +138,8 @@ public:
      * Returns the first 64 bits from the resulting hash.
      */
     inline uint64_t GetCheapHash() {
-        unsigned char result[CHash256::OUTPUT_SIZE];
-        ctx.Finalize(result);
-        return ReadLE64(result);
+        uint256 result = GetHash();
+        return ReadLE64(result.begin());
     }
 
     template<typename T>