Add Scale to SingleAssetVault (#5652)

* Add and Scale to VaultCreate
* Add round-trip calculation to VaultDeposit VaultWithdraw and VaultClawback
* Implement Number::truncate() for VaultClawback
* Add rounding to DepositWithdraw
* Disallow zero shares withdraw or deposit with tecPRECISION_LOSS
* Return tecPATH_DRY on overflow when converting shares/assets
* Remove empty shares MPToken in clawback or withdraw (except for vault owner)
* Implicitly create shares MPToken for vault owner in VaultCreate
* Review feedback: defensive checks in shares/assets calculations

---------

Co-authored-by: Ed Hennis <[email protected]>

Author: Bronek

include/xrpl/basics/Number.h

@@ -150,6 +150,24 @@ class Number
         return (mantissa_ < 0) ? -1 : (mantissa_ ? 1 : 0);
     }
 
+    Number
+    truncate() const noexcept
+    {
+        if (exponent_ >= 0 || mantissa_ == 0)
+            return *this;
+
+        Number ret = *this;
+        while (ret.exponent_ < 0 && ret.mantissa_ != 0)
+        {
+            ret.exponent_ += 1;
+            ret.mantissa_ /= rep(10);
+        }
+        // We are guaranteed that normalize() will never throw an exception
+        // because exponent is either negative or zero at this point.
+        ret.normalize();
+        return ret;
+    }
+
     friend constexpr bool
     operator>(Number const& x, Number const& y) noexcept
     {

include/xrpl/protocol/Protocol.h

@@ -122,6 +122,13 @@ std::size_t constexpr maxDataPayloadLength = 256;
 /** Vault withdrawal policies */
 std::uint8_t constexpr vaultStrategyFirstComeFirstServe = 1;
 
+/** Default IOU scale factor for a Vault */
+std::uint8_t constexpr vaultDefaultIOUScale = 6;
+/** Maximum scale factor for a Vault. The number is chosen to ensure that
+1 IOU can be always converted to shares.
+10^19 > maxMPTokenAmount (2^64-1) > 10^18 */
+std::uint8_t constexpr vaultMaximumIOUScale = 18;
+
 /** Maximum recursion depth for vault shares being put as an asset inside
  * another vault; counted from 0 */
 std::uint8_t constexpr maxAssetCheckDepth = 5;

include/xrpl/protocol/detail/ledger_entries.macro

@@ -499,6 +499,7 @@ LEDGER_ENTRY(ltVAULT, 0x0084, Vault, vault, ({
     {sfLossUnrealized,       soeREQUIRED},
     {sfShareMPTID,           soeREQUIRED},
     {sfWithdrawalPolicy,     soeREQUIRED},
+    {sfScale,                soeDEFAULT},
     // no SharesTotal ever (use MPTIssuance.sfOutstandingAmount)
     // no PermissionedDomainID ever (use MPTIssuance.sfDomainID)
 }))

include/xrpl/protocol/detail/transactions.macro

@@ -483,6 +483,7 @@ TRANSACTION(ttVAULT_CREATE, 65, VaultCreate, Delegation::delegatable, ({
     {sfDomainID, soeOPTIONAL},
     {sfWithdrawalPolicy, soeOPTIONAL},
     {sfData, soeOPTIONAL},
+    {sfScale, soeOPTIONAL},
 }))
 
 /** This transaction updates a single asset vault. */