refactor: Use uint64_t over size_t for serialized-size values

The values are small enough to fit in size_t, but to avoid having to
think about it, just use uint64_t consistently for all architectures.

On 64-bit systems, this refactor is a no-op. On 32-bit systems, it could
avoid bugs in the theoretical and unexpected case where a 32-bit size_t
is too small and overflows.

src/coins.cpp

@@ -349,8 +349,8 @@ void CCoinsViewCache::SanityCheck() const
     assert(recomputed_usage == cachedCoinsUsage);
 }
 
-static const size_t MIN_TRANSACTION_OUTPUT_WEIGHT = WITNESS_SCALE_FACTOR * ::GetSerializeSize(CTxOut());
-static const size_t MAX_OUTPUTS_PER_BLOCK = MAX_BLOCK_WEIGHT / MIN_TRANSACTION_OUTPUT_WEIGHT;
+static const uint64_t MIN_TRANSACTION_OUTPUT_WEIGHT{WITNESS_SCALE_FACTOR * ::GetSerializeSize(CTxOut())};
+static const uint64_t MAX_OUTPUTS_PER_BLOCK{MAX_BLOCK_WEIGHT / MIN_TRANSACTION_OUTPUT_WEIGHT};
 
 const Coin& AccessByTxid(const CCoinsViewCache& view, const Txid& txid)
 {

src/index/blockfilterindex.cpp

@@ -202,9 +202,9 @@ size_t BlockFilterIndex::WriteFilterToDisk(FlatFilePos& pos, const BlockFilter&
 {
     assert(filter.GetFilterType() == GetFilterType());
 
-    size_t data_size =
+    uint64_t data_size{
         GetSerializeSize(filter.GetBlockHash()) +
-        GetSerializeSize(filter.GetEncodedFilter());
+        GetSerializeSize(filter.GetEncodedFilter())};
 
     // If writing the filter would overflow the file, flush and move to the next one.
     if (pos.nPos + data_size > MAX_FLTR_FILE_SIZE) {

src/policy/policy.cpp

@@ -42,7 +42,7 @@ CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)
     if (txout.scriptPubKey.IsUnspendable())
         return 0;
 
-    size_t nSize = GetSerializeSize(txout);
+    uint64_t nSize{GetSerializeSize(txout)};
     int witnessversion = 0;
     std::vector<unsigned char> witnessprogram;
 

src/rpc/blockchain.cpp

@@ -2033,7 +2033,7 @@ static RPCHelpMan getblockstats()
             for (const CTxOut& out : tx->vout) {
                 tx_total_out += out.nValue;
 
-                size_t out_size = GetSerializeSize(out) + PER_UTXO_OVERHEAD;
+                uint64_t out_size{GetSerializeSize(out) + PER_UTXO_OVERHEAD};
                 utxo_size_inc += out_size;
 
                 // The Genesis block and the repeated BIP30 block coinbases don't change the UTXO
@@ -2085,7 +2085,7 @@ static RPCHelpMan getblockstats()
                 const CTxOut& prevoutput = coin.out;
 
                 tx_total_in += prevoutput.nValue;
-                size_t prevout_size = GetSerializeSize(prevoutput) + PER_UTXO_OVERHEAD;
+                uint64_t prevout_size{GetSerializeSize(prevoutput) + PER_UTXO_OVERHEAD};
                 utxo_size_inc -= prevout_size;
                 utxo_size_inc_actual -= prevout_size;
             }

src/test/flatfile_tests.cpp

@@ -39,8 +39,8 @@ BOOST_AUTO_TEST_CASE(flatfile_open)
     std::string line2("Digital signatures provide part of the solution, but the main benefits are "
                       "lost if a trusted third party is still required to prevent double-spending.");
 
-    size_t pos1 = 0;
-    size_t pos2 = pos1 + GetSerializeSize(line1);
+    uint64_t pos1{0};
+    uint64_t pos2{pos1 + GetSerializeSize(line1)};
 
     // Write first line to file.
     {

src/test/fuzz/miniscript.cpp

@@ -1120,7 +1120,7 @@ void TestNode(const MsCtx script_ctx, const NodeRef& node, FuzzedDataProvider& p
         assert(mal_success);
         assert(stack_nonmal == stack_mal);
         // Compute witness size (excluding script push, control block, and witness count encoding).
-        const size_t wit_size = GetSerializeSize(stack_nonmal) - GetSizeOfCompactSize(stack_nonmal.size());
+        const uint64_t wit_size{GetSerializeSize(stack_nonmal) - GetSizeOfCompactSize(stack_nonmal.size())};
         assert(wit_size <= *node->GetWitnessSize());
 
         // Test non-malleable satisfaction.

src/test/miner_tests.cpp

@@ -188,7 +188,7 @@ void MinerTestingSetup::TestPackageSelection(const CScript& scriptPubKey, const
     tx.vout[0].nValue = 5000000000LL - 1000 - 50000; // 0 fee
     Txid hashFreeTx = tx.GetHash();
     AddToMempool(tx_mempool, entry.Fee(0).FromTx(tx));
-    size_t freeTxSize = ::GetSerializeSize(TX_WITH_WITNESS(tx));
+    uint64_t freeTxSize{::GetSerializeSize(TX_WITH_WITNESS(tx))};
 
     // Calculate a fee on child transaction that will put the package just
     // below the block min tx fee (assuming 1 child tx of the same size).

src/test/miniscript_tests.cpp

@@ -372,7 +372,7 @@ void TestSatisfy(const KeyConverter& converter, const std::string& testcase, con
             CScriptWitness witness_nonmal;
             const bool nonmal_success = node->Satisfy(satisfier, witness_nonmal.stack, true) == miniscript::Availability::YES;
             // Compute witness size (excluding script push, control block, and witness count encoding).
-            const size_t wit_size = GetSerializeSize(witness_nonmal.stack) - GetSizeOfCompactSize(witness_nonmal.stack.size());
+            const uint64_t wit_size{GetSerializeSize(witness_nonmal.stack) - GetSizeOfCompactSize(witness_nonmal.stack.size())};
             SatisfactionToWitness(converter.MsContext(), witness_nonmal, script, builder);
 
             if (nonmal_success) {

src/wallet/spend.cpp

@@ -1034,7 +1034,7 @@ void DiscourageFeeSniping(CMutableTransaction& tx, FastRandomContext& rng_fast,
     }
 }
 
-size_t GetSerializeSizeForRecipient(const CRecipient& recipient)
+uint64_t GetSerializeSizeForRecipient(const CRecipient& recipient)
 {
     return ::GetSerializeSize(CTxOut(recipient.nAmount, GetScriptForDestination(recipient.dest)));
 }