refactor: define a UINT256_ONE global constant

Instead of having a uint256 representations of one scattered throughout
where it is used, define it globally in uint256.h

src/script/interpreter.cpp

@@ -1281,13 +1281,11 @@ uint256 SignatureHash(const CScript& scriptCode, const T& txTo, unsigned int nIn
         return ss.GetHash();
     }
 
-    static const uint256 one(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
-
     // Check for invalid use of SIGHASH_SINGLE
     if ((nHashType & 0x1f) == SIGHASH_SINGLE) {
         if (nIn >= txTo.vout.size()) {
             //  nOut out of range
-            return one;
+            return UINT256_ONE();
         }
     }
 

src/test/sighash_tests.cpp

@@ -26,10 +26,9 @@ extern UniValue read_json(const std::string& jsondata);
 // Old script.cpp SignatureHash function
 uint256 static SignatureHashOld(CScript scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType)
 {
-    static const uint256 one(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
     if (nIn >= txTo.vin.size())
     {
-        return one;
+        return UINT256_ONE();
     }
     CMutableTransaction txTmp(txTo);
 
@@ -59,7 +58,7 @@ uint256 static SignatureHashOld(CScript scriptCode, const CTransaction& txTo, un
         unsigned int nOut = nIn;
         if (nOut >= txTmp.vout.size())
         {
-            return one;
+            return UINT256_ONE();
         }
         txTmp.vout.resize(nOut+1);
         for (unsigned int i = 0; i < nOut; i++)

src/uint256.cpp

@@ -75,3 +75,8 @@ template std::string base_blob<256>::GetHex() const;
 template std::string base_blob<256>::ToString() const;
 template void base_blob<256>::SetHex(const char*);
 template void base_blob<256>::SetHex(const std::string&);
+
+uint256& UINT256_ONE() {
+    static uint256* one = new uint256(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
+    return *one;
+}

src/uint256.h

@@ -144,4 +144,6 @@ inline uint256 uint256S(const std::string& str)
     return rv;
 }
 
+uint256& UINT256_ONE();
+
 #endif // BITCOIN_UINT256_H

src/wallet/wallet.cpp

@@ -238,7 +238,7 @@ WalletCreationStatus CreateWallet(interfaces::Chain& chain, const SecureString&
     return WalletCreationStatus::SUCCESS;
 }
 
-const uint256 CWalletTx::ABANDON_HASH(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
+const uint256 CWalletTx::ABANDON_HASH(UINT256_ONE());
 
 /** @defgroup mapWallet
  *