store outPk/8 in the tx for speed

It avoids dividing by 8 when deserializing a tx, which is a slow
operation, and multiplies by 8 when verifying and extracing the
amount, which is much faster as well as less frequent

src/blockchain_db/blockchain_db.cpp

@@ -241,8 +241,15 @@ void BlockchainDB::add_transaction(const crypto::hash& blk_hash, const std::pair
     }
     else
     {
+      rct::key commitment;
+      if (tx.version > 1)
+      {
+        commitment = tx.rct_signatures.outPk[i].mask;
+        if (rct::is_rct_bulletproof_plus(tx.rct_signatures.type))
+          commitment = rct::scalarmult8(commitment);
+      }
       amount_output_indices[i] = add_output(tx_hash, tx.vout[i], i, tx.unlock_time,
-        tx.version > 1 ? &tx.rct_signatures.outPk[i].mask : NULL);
+        tx.version > 1 ? &commitment : NULL);
     }
   }
   add_tx_amount_output_indices(tx_id, amount_output_indices);

src/cryptonote_basic/cryptonote_format_utils.cpp

@@ -189,7 +189,7 @@ namespace cryptonote
           CHECK_AND_ASSERT_MES(n_amounts == rv.outPk.size(), false, "Internal error filling out V");
           rv.p.bulletproofs_plus[0].V.resize(n_amounts);
           for (size_t i = 0; i < n_amounts; ++i)
-            rv.p.bulletproofs_plus[0].V[i] = rct::scalarmultKey(rv.outPk[i].mask, rct::INV_EIGHT);
+            rv.p.bulletproofs_plus[0].V[i] = rv.outPk[i].mask;
         }
         else if (bulletproof)
         {

src/ringct/rctSigs.cpp

@@ -1205,7 +1205,7 @@ namespace rct {
         rv.p.bulletproofs_plus.clear();
         if (bulletproof_or_plus)
         {
-            const bool plus = rv.type == RCTTypeBulletproofPlus;
+            const bool plus = is_rct_bulletproof_plus(rv.type);
             size_t n_amounts = outamounts.size();
             size_t amounts_proved = 0;
             if (rct_config.range_proof_type == RangeProofPaddedBulletproof)
@@ -1235,6 +1235,9 @@ namespace rct {
                 }
                 for (i = 0; i < outamounts.size(); ++i)
                 {
+                    if (plus)
+                      rv.outPk[i].mask = C[i];
+                    else
                       rv.outPk[i].mask = rct::scalarmult8(C[i]);
                     outSk[i].mask = masks[i];
                 }
@@ -1273,6 +1276,9 @@ namespace rct {
                 }
                 for (i = 0; i < batch_size; ++i)
                 {
+                  if (plus)
+                    rv.outPk[i + amounts_proved].mask = C[i];
+                  else
                     rv.outPk[i + amounts_proved].mask = rct::scalarmult8(C[i]);
                   outSk[i + amounts_proved].mask = masks[i];
                 }
@@ -1480,6 +1486,9 @@ namespace rct {
 
           rct::keyV masks(rv.outPk.size());
           for (size_t i = 0; i < rv.outPk.size(); i++) {
+            if (bulletproof_plus)
+              masks[i] = rct::scalarmult8(rv.outPk[i].mask);
+            else
               masks[i] = rv.outPk[i].mask;
           }
           key sumOutpks = addKeys(masks);
@@ -1640,6 +1649,8 @@ namespace rct {
         mask = ecdh_info.mask;
         key amount = ecdh_info.amount;
         key C = rv.outPk[i].mask;
+        if (is_rct_bulletproof_plus(rv.type))
+          C = scalarmult8(C);
         DP("C");
         DP(C);
         key Ctmp;
@@ -1671,6 +1682,8 @@ namespace rct {
         mask = ecdh_info.mask;
         key amount = ecdh_info.amount;
         key C = rv.outPk[i].mask;
+        if (is_rct_bulletproof_plus(rv.type))
+          C = scalarmult8(C);
         DP("C");
         DP(C);
         key Ctmp;

src/wallet/wallet2.cpp

@@ -11290,7 +11290,9 @@ void wallet2::check_tx_key_helper(const cryptonote::transaction &tx, const crypt
         crypto::derivation_to_scalar(found_derivation, n, scalar1);
         rct::ecdhTuple ecdh_info = tx.rct_signatures.ecdhInfo[n];
         rct::ecdhDecode(ecdh_info, rct::sk2rct(scalar1), tx.rct_signatures.type == rct::RCTTypeBulletproof2 || tx.rct_signatures.type == rct::RCTTypeCLSAG || tx.rct_signatures.type == rct::RCTTypeBulletproofPlus);
-        const rct::key C = tx.rct_signatures.outPk[n].mask;
+        rct::key C = tx.rct_signatures.outPk[n].mask;
+        if (rct::is_rct_bulletproof_plus(tx.rct_signatures.type))
+          C = rct::scalarmult8(C);
         rct::key Ctmp;
         THROW_WALLET_EXCEPTION_IF(sc_check(ecdh_info.mask.bytes) != 0, error::wallet_internal_error, "Bad ECDH input mask");
         THROW_WALLET_EXCEPTION_IF(sc_check(ecdh_info.amount.bytes) != 0, error::wallet_internal_error, "Bad ECDH input amount");

tests/core_tests/multisig.cpp

@@ -450,6 +450,8 @@ bool gen_multisig_tx_validation_base::generate_with(std::vector<test_event_entry
       rct::ecdhTuple ecdh_info = tx.rct_signatures.ecdhInfo[n];
       rct::ecdhDecode(ecdh_info, rct::sk2rct(scalar1), tx.rct_signatures.type == rct::RCTTypeBulletproof2 || tx.rct_signatures.type == rct::RCTTypeCLSAG || tx.rct_signatures.type == rct::RCTTypeBulletproofPlus);
       rct::key C = tx.rct_signatures.outPk[n].mask;
+      if (rct::is_rct_bulletproof_plus(tx.rct_signatures.type))
+        C = rct::scalarmult8(C);
       rct::addKeys2(Ctmp, ecdh_info.mask, ecdh_info.amount, rct::H);
       CHECK_AND_ASSERT_MES(rct::equalKeys(C, Ctmp), false, "Failed to decode amount");
       amount += rct::h2d(ecdh_info.amount);