Reduce STAmount public interface (RIPD-867):

* Implement subtraction as addition to the additive inverse
* Do not allow comparison with, addition to or subtraction from integers
* Remove unused functions
* Convert member functions to free functions
* Isolate unit-test specific code into the unit test

src/ripple/app/tx/impl/CreateOffer.cpp

@@ -430,7 +430,7 @@ private:
     {
         std::string txt = amount.getText ();
         txt += "/";
-        txt += amount.getHumanCurrency ();
+        txt += to_string (amount.issue().currency);
         return txt;
     }
 
@@ -451,11 +451,11 @@ public:
     }
 
     /** Returns the reserve the account would have if an offer was added. */
-    std::uint32_t
+    STAmount
     getAccountReserve (SLE::pointer account)
     {
-        return mEngine->getLedger ()->getReserve (
-            account->getFieldU32 (sfOwnerCount) + 1);
+        return STAmount (mEngine->getLedger ()->getReserve (
+            account->getFieldU32 (sfOwnerCount) + 1));
     }
 
     TER
@@ -504,7 +504,7 @@ public:
         if (!isLegalNet (saTakerPays) || !isLegalNet (saTakerGets))
             return temBAD_AMOUNT;
 
-        if (saTakerPays.isNative () && saTakerGets.isNative ())
+        if (saTakerPays.native () && saTakerGets.native ())
         {
             if (m_journal.debug) m_journal.warning <<
                 "Malformed offer: XRP for XRP";
@@ -537,8 +537,8 @@ public:
             return temBAD_CURRENCY;
         }
 
-        if (saTakerPays.isNative () != !uPaysIssuerID ||
-            saTakerGets.isNative () != !uGetsIssuerID)
+        if (saTakerPays.native () != !uPaysIssuerID ||
+            saTakerGets.native () != !uGetsIssuerID)
         {
             if (m_journal.warning) m_journal.warning <<
                 "Malformed offer: bad issuer";
@@ -660,7 +660,7 @@ public:
         }
 
         // Make sure that we are authorized to hold what the taker will pay us.
-        if (result == tesSUCCESS && !saTakerPays.isNative ())
+        if (result == tesSUCCESS && !saTakerPays.native ())
             result = checkAcceptAsset (Issue (uPaysCurrency, uPaysIssuerID));
 
         bool const bOpenLedger (mParams & tapOPEN_LEDGER);
@@ -858,8 +858,8 @@ transact_CreateOffer (
 {
     CrossType cross_type = CrossType::IouToIou;
 
-    bool const pays_xrp = txn.getFieldAmount (sfTakerPays).isNative ();
-    bool const gets_xrp = txn.getFieldAmount (sfTakerGets).isNative ();
+    bool const pays_xrp = txn.getFieldAmount (sfTakerPays).native ();
+    bool const gets_xrp = txn.getFieldAmount (sfTakerGets).native ();
 
     if (pays_xrp && !gets_xrp)
         cross_type = CrossType::IouToXrp;

src/ripple/app/tx/impl/CreateTicket.cpp

@@ -57,17 +57,22 @@ public:
         return Transactor::preCheck ();
     }
 
+    /** Returns the reserve the account would have if an offer was added. */
+    STAmount
+    getAccountReserve (SLE::pointer account)
+    {
+        return STAmount (mEngine->getLedger ()->getReserve (
+            account->getFieldU32 (sfOwnerCount) + 1));
+    }
+
     TER doApply () override
     {
         assert (mTxnAccount);
 
-        // A ticket counts against the reserve of the issuing account, but we check
-        // the starting balance because we want to allow dipping into the reserve to
-        // pay fees.
-        auto const accountReserve (mEngine->getLedger ()->getReserve (
-            mTxnAccount->getFieldU32 (sfOwnerCount) + 1));
-
-        if (mPriorBalance < accountReserve)
+        // A ticket counts against the reserve of the issuing account, but we
+        // check the starting balance because we want to allow dipping into the
+        // reserve to pay fees.
+        if (mPriorBalance < getAccountReserve (mTxnAccount))
             return tecINSUFFICIENT_RESERVE;
 
         std::uint32_t expiration (0);

src/ripple/app/tx/impl/Payment.cpp

@@ -73,7 +73,7 @@ public:
 
         if (bMax)
             maxSourceAmount = mTxn.getFieldAmount (sfSendMax);
-        else if (saDstAmount.isNative ())
+        else if (saDstAmount.native ())
             maxSourceAmount = saDstAmount;
         else
             maxSourceAmount = STAmount (
@@ -178,7 +178,7 @@ public:
         STAmount maxSourceAmount;
         if (bMax)
             maxSourceAmount = mTxn.getFieldAmount (sfSendMax);
-        else if (saDstAmount.isNative ())
+        else if (saDstAmount.native ())
             maxSourceAmount = saDstAmount;
         else
           maxSourceAmount = STAmount (
@@ -197,7 +197,7 @@ public:
         if (!sleDst)
         {
             // Destination account does not exist.
-            if (!saDstAmount.isNative ())
+            if (!saDstAmount.native ())
             {
                 m_journal.trace <<
                     "Delay transaction: Destination account does not exist.";
@@ -218,7 +218,7 @@ public:
                 // transaction would succeed.
                 return telNO_DST_PARTIAL;
             }
-            else if (saDstAmount < mEngine->getLedger ()->getReserve (0))
+            else if (saDstAmount < STAmount (mEngine->getLedger ()->getReserve (0)))
             {
                 // getReserve() is the minimum amount that an account can have.
                 // Reserve is not scaled by load.
@@ -260,7 +260,7 @@ public:
 
         TER terResult;
 
-        bool const bRipple = bPaths || bMax || !saDstAmount.isNative ();
+        bool const bRipple = bPaths || bMax || !saDstAmount.native ();
         // XXX Should bMax be sufficient to imply ripple?
 
         if (bRipple)
@@ -331,37 +331,39 @@ public:
         {
             // Direct XRP payment.
 
-            // uOwnerCount is the number of entries in this legder for this account
-            // that require a reserve.
-
-            std::uint32_t const uOwnerCount (mTxnAccount->getFieldU32 (sfOwnerCount));
+            // uOwnerCount is the number of entries in this legder for this
+            // account that require a reserve.
+            auto const uOwnerCount = mTxnAccount->getFieldU32 (sfOwnerCount);
 
             // This is the total reserve in drops.
-            // TODO(tom): there should be a class for this.
-            std::uint64_t const uReserve (mEngine->getLedger ()->getReserve (uOwnerCount));
+            std::uint64_t const uReserve =
+                mEngine->getLedger ()->getReserve (uOwnerCount);
+
+            // mPriorBalance is the balance on the sending account BEFORE the
+            // fees were charged. We want to make sure we have enough reserve
+            // to send. Allow final spend to use reserve for fee.
+            auto const mmm = std::max(mTxn.getTransactionFee (),
+                STAmount (uReserve));
 
-            // mPriorBalance is the balance on the sending account BEFORE the fees were charged.
-            //
-            // Make sure have enough reserve to send. Allow final spend to use
-            // reserve for fee.
-            auto const mmm = std::max(uReserve, getNValue (mTxn.getTransactionFee ()));
             if (mPriorBalance < saDstAmount + mmm)
             {
-                // Vote no.
-                // However, transaction might succeed, if applied in a different order.
+                // Vote no. However the transaction might succeed, if applied in
+                // a different order.
                 m_journal.trace << "Delay transaction: Insufficient funds: " <<
                     " " << mPriorBalance.getText () <<
-                    " / " << (saDstAmount + uReserve).getText () <<
+                    " / " << (saDstAmount + mmm).getText () <<
                     " (" << uReserve << ")";
 
                 terResult = tecUNFUNDED_PAYMENT;
             }
             else
             {
-                // The source account does have enough money, so do the arithmetic
-                // for the transfer and make the ledger change.
-                mTxnAccount->setFieldAmount (sfBalance, mSourceBalance - saDstAmount);
-                sleDst->setFieldAmount (sfBalance, sleDst->getFieldAmount (sfBalance) + saDstAmount);
+                // The source account does have enough money, so do the
+                // arithmetic for the transfer and make the ledger change.
+                mTxnAccount->setFieldAmount (sfBalance,
+                    mSourceBalance - saDstAmount);
+                sleDst->setFieldAmount (sfBalance,
+                    sleDst->getFieldAmount (sfBalance) + saDstAmount);
 
                 // Re-arm the password change fee if we can and need to.
                 if ((sleDst->getFlags () & lsfPasswordSpent))

src/ripple/app/tx/impl/SetTrust.cpp

@@ -58,7 +58,7 @@ public:
         if (!isLegalNet (saLimitAmount))
             return temBAD_AMOUNT;
 
-        if (saLimitAmount.isNative ())
+        if (saLimitAmount.native ())
         {
             if (m_journal.trace) m_journal.trace <<
                 "Malformed transaction: specifies native limit " <<
@@ -121,9 +121,9 @@ public:
         // to fund accounts in a way where there's no incentive to trick them
         // into creating an account you have no intention of using.
 
-        std::uint64_t const uReserveCreate = (uOwnerCount < 2)
+        STAmount const reserveCreate ((uOwnerCount < 2)
             ? 0
-            : mEngine->getLedger ()->getReserve (uOwnerCount + 1);
+            : mEngine->getLedger ()->getReserve (uOwnerCount + 1));
 
         std::uint32_t uQualityIn (bQualityIn ? mTxn.getFieldU32 (sfQualityIn) : 0);
         std::uint32_t uQualityOut (bQualityOut ? mTxn.getFieldU32 (sfQualityOut) : 0);
@@ -380,7 +380,7 @@ public:
                 terResult = mEngine->view ().trustDelete (sleRippleState, uLowAccountID, uHighAccountID);
             }
             // Reserve is not scaled by load.
-            else if (bReserveIncrease && mPriorBalance < uReserveCreate)
+            else if (bReserveIncrease && mPriorBalance < reserveCreate)
             {
                 m_journal.trace <<
                     "Delay transaction: Insufficent reserve to add trust line.";
@@ -405,7 +405,7 @@ public:
                 "Redundant: Setting non-existent ripple line to defaults.";
             return tecNO_LINE_REDUNDANT;
         }
-        else if (mPriorBalance < uReserveCreate) // Reserve is not scaled by load.
+        else if (mPriorBalance < reserveCreate) // Reserve is not scaled by load.
         {
             m_journal.trace <<
                 "Delay transaction: Line does not exist. Insufficent reserve to create line.";

src/ripple/app/tx/impl/Taker.cpp

@@ -360,10 +360,10 @@ BasicTaker::do_cross (
 {
     assert (!done ());
 
-    assert (!offer1.in.isNative ());
-    assert (offer1.out.isNative ());
-    assert (offer2.in.isNative ());
-    assert (!offer2.out.isNative ());
+    assert (!offer1.in.native ());
+    assert (offer1.out.native ());
+    assert (offer2.in.native ());
+    assert (!offer2.out.native ());
 
     // If the taker owns the first leg of the offer, then the taker's available
     // funds aren't the limiting factor for the input - the offer itself is.

src/ripple/app/tx/impl/Transactor.cpp

@@ -126,7 +126,7 @@ TER Transactor::payFee ()
         return telINSUF_FEE_P;
     }
 
-    if (saPaid < zero || !saPaid.isNative ())
+    if (saPaid < zero || !saPaid.native ())
         return temBAD_FEE;
 
     if (!saPaid)
@@ -307,13 +307,11 @@ TER Transactor::checkSign ()
 {
 #if RIPPLE_ENABLE_MULTI_SIGN
     // If the mSigningPubKey is empty, then we must be multi-signing.
-    TER const signingTER = mSigningPubKey.getAccountPublic ().empty () ?
-        checkMultiSign () : checkSingleSign ();
-#else
-    TER const signingTER = checkSingleSign ();
-#endif // RIPPLE_ENABLE_MULTI_SIGN
+    if (mSigningPubKey.getAccountPublic ().empty ())
+        return checkMultiSign ();
+#endif
 
-    return signingTER;
+    return checkSingleSign ();
 }
 
 TER Transactor::checkSingleSign ()

src/ripple/app/tx/tests/Taker.test.cpp

@@ -128,9 +128,7 @@ private:
 
     STAmount parse_amount (std::string const& amount, Issue const& issue)
     {
-        STAmount result (issue);
-        expect (result.setValue (amount), amount);
-        return result;
+        return amountFromString (issue, amount);
     }
 
     Amounts parse_amounts (
@@ -162,7 +160,7 @@ private:
     {
         std::string txt = amount.getText ();
         txt += "/";
-        txt += amount.getHumanCurrency ();
+        txt += to_string (amount.issue().currency);
         return txt;
     }
 
@@ -212,7 +210,7 @@ private:
         Amounts const expected (parse_amounts (
             flow.in, issue_in,
             flow.out, issue_out));
-        
+
         expect (expected == result, name + (sell ? " (s)" : " (b)"));
 
         if (expected != result)
@@ -233,7 +231,7 @@ private:
 
 public:
     // Notation for clamp scenario descriptions:
-    // 
+    //
     // IN:OUT (with the last in the list being limiting factor)
     //  N  = Nothing
     //  T  = Taker Offer Balance

src/ripple/app/tx/tests/common_transactor.cpp

@@ -362,7 +362,7 @@ void payInDrops (TestLedger& ledger,
 
 std::uint64_t getNativeBalance(TestLedger& ledger, UserAccount& acct)
 {
-    return getNValue(ledger.getAccountState(acct)->getBalance());
+    return ledger.getAccountState(acct)->getBalance().mantissa ();
 }
 
 std::uint32_t getOwnerCount(TestLedger& ledger, UserAccount& acct)