Partially implement Lending Protocol (#5270)

- Spec: XLS-66
- Introduces amendment "featureLendingProtocol", but leaves it
  UNSUPPORTED to allow for future development work.
- AccountInfo RPC will indicate the type of pseudo-account when
  appropriate.
- Refactors and improves several existing classes and functional areas,
  including Number, STAmount, STObject, json_value, Asset, directory
  handling, View helper functions, and unit test helpers.

Author: ximinez

include/xrpl/basics/Number.h

@@ -13,6 +13,15 @@ class Number;
 std::string
 to_string(Number const& amount);
 
+template <typename T>
+constexpr bool
+isPowerOfTen(T value)
+{
+    while (value >= 10 && value % 10 == 0)
+        value /= 10;
+    return value == 1;
+}
+
 class Number
 {
     using rep = std::int64_t;
@@ -22,7 +31,9 @@ class Number
 public:
     // The range for the mantissa when normalized
     constexpr static std::int64_t minMantissa = 1'000'000'000'000'000LL;
-    constexpr static std::int64_t maxMantissa = 9'999'999'999'999'999LL;
+    static_assert(isPowerOfTen(minMantissa));
+    constexpr static std::int64_t maxMantissa = minMantissa * 10 - 1;
+    static_assert(maxMantissa == 9'999'999'999'999'999LL);
 
     // The range for the exponent when normalized
     constexpr static int minExponent = -32768;
@@ -132,22 +143,7 @@ class Number
     }
 
     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;
-    }
+    truncate() const noexcept;
 
     friend constexpr bool
     operator>(Number const& x, Number const& y) noexcept
@@ -192,6 +188,8 @@ class Number
     class Guard;
 };
 
+constexpr static Number numZero{};
+
 inline constexpr Number::Number(rep mantissa, int exponent, unchecked) noexcept
     : mantissa_{mantissa}, exponent_{exponent}
 {

include/xrpl/beast/utility/instrumentation.h

@@ -13,7 +13,7 @@
 // The duplication is because Visual Studio 2019 cannot compile that header
 // even with the option -Zc:__cplusplus added.
 #define ALWAYS(cond, message, ...) assert((message) && (cond))
-#define ALWAYS_OR_UNREACHABLE(cond, message, ...) assert((message) && (cond))
+#define ALWAYS_OR_UNREACHABLE(cond, message) assert((message) && (cond))
 #define SOMETIMES(cond, message, ...)
 #define REACHABLE(message, ...)
 #define UNREACHABLE(message, ...) assert((message) && false)

include/xrpl/json/json_value.h

@@ -381,6 +381,9 @@ class Value
     /// Return true if the object has a member named key.
     bool
     isMember(std::string const& key) const;
+    /// Return true if the object has a member named key.
+    bool
+    isMember(StaticString const& key) const;
 
     /// \brief Return a list of the member names.
     ///

include/xrpl/ledger/ApplyView.h

@@ -368,6 +368,45 @@ class ApplyView : public ReadView
     emptyDirDelete(Keylet const& directory);
 };
 
+namespace directory {
+/** Helper functions for managing low-level directory operations.
+    These are not part of the ApplyView interface.
+
+    Don't use them unless you really, really know what you're doing.
+    Instead use dirAdd, dirInsert, etc.
+ */
+
+std::uint64_t
+createRoot(
+    ApplyView& view,
+    Keylet const& directory,
+    uint256 const& key,
+    std::function<void(std::shared_ptr<SLE> const&)> const& describe);
+
+auto
+findPreviousPage(ApplyView& view, Keylet const& directory, SLE::ref start);
+
+std::uint64_t
+insertKey(
+    ApplyView& view,
+    SLE::ref node,
+    std::uint64_t page,
+    bool preserveOrder,
+    STVector256& indexes,
+    uint256 const& key);
+
+std::optional<std::uint64_t>
+insertPage(
+    ApplyView& view,
+    std::uint64_t page,
+    SLE::pointer node,
+    std::uint64_t nextPage,
+    SLE::ref next,
+    uint256 const& key,
+    Keylet const& directory,
+    std::function<void(std::shared_ptr<SLE> const&)> const& describe);
+
+}  // namespace directory
 }  // namespace ripple
 
 #endif