Remove undefined behavior

* Taking the negative of a signed negative is UB, but
  taking the negative of an unsigned is not.

src/ripple/basics/impl/IOUAmount.cpp

@@ -45,6 +45,12 @@ IOUAmount::minPositiveAmount()
 void
 IOUAmount::normalize()
 {
+    if (mantissa_ == 0)
+    {
+        *this = beast::zero;
+        return;
+    }
+
     if (*stNumberSwitchover)
     {
         Number v{mantissa_, exponent_};
@@ -56,11 +62,6 @@ IOUAmount::normalize()
             *this = beast::zero;
         return;
     }
-    if (mantissa_ == 0)
-    {
-        *this = beast::zero;
-        return;
-    }
 
     bool const negative = (mantissa_ < 0);
 
@@ -107,48 +108,46 @@ IOUAmount::IOUAmount(Number const& other)
 IOUAmount&
 IOUAmount::operator+=(IOUAmount const& other)
 {
+    if (other == beast::zero)
+        return *this;
+
+    if (*this == beast::zero)
+    {
+        *this = other;
+        return *this;
+    }
+
     if (*stNumberSwitchover)
     {
         *this = IOUAmount{Number{*this} + Number{other}};
+        return *this;
     }
-    else
+    auto m = other.mantissa_;
+    auto e = other.exponent_;
+
+    while (exponent_ < e)
     {
-        if (other == beast::zero)
-            return *this;
-
-        if (*this == beast::zero)
-        {
-            *this = other;
-            return *this;
-        }
-
-        auto m = other.mantissa_;
-        auto e = other.exponent_;
-
-        while (exponent_ < e)
-        {
-            mantissa_ /= 10;
-            ++exponent_;
-        }
-
-        while (e < exponent_)
-        {
-            m /= 10;
-            ++e;
-        }
-
-        // This addition cannot overflow an std::int64_t but we may throw from
-        // normalize if the result isn't representable.
-        mantissa_ += m;
-
-        if (mantissa_ >= -10 && mantissa_ <= 10)
-        {
-            *this = beast::zero;
-            return *this;
-        }
-
-        normalize();
+        mantissa_ /= 10;
+        ++exponent_;
     }
+
+    while (e < exponent_)
+    {
+        m /= 10;
+        ++e;
+    }
+
+    // This addition cannot overflow an std::int64_t but we may throw from
+    // normalize if the result isn't representable.
+    mantissa_ += m;
+
+    if (mantissa_ >= -10 && mantissa_ <= 10)
+    {
+        *this = beast::zero;
+        return *this;
+    }
+
+    normalize();
     return *this;
 }
 

src/ripple/basics/impl/Number.cpp

@@ -25,7 +25,7 @@
 #include <type_traits>
 #include <utility>
 
-#ifdef _MSVC_LANG
+#ifdef BOOST_COMP_MSVC
 #include <boost/multiprecision/cpp_int.hpp>
 using uint128_t = boost::multiprecision::uint128_t;
 #else   // !defined(_MSVC_LANG)
@@ -130,34 +130,37 @@ int
 Number::Guard::round() noexcept
 {
     auto mode = Number::getround();
-    switch (mode)
+
+    if (mode == towards_zero)
+        return -1;
+
+    if (mode == downward)
     {
-        // round to nearest if mode is not one of the predefined values
-        default:
-        case to_nearest:
-            if (digits_ > 0x5000'0000'0000'0000)
-                return 1;
-            if (digits_ < 0x5000'0000'0000'0000)
-                return -1;
-            if (xbit_)
-                return 1;
-            return 0;
-        case towards_zero:
-            return -1;
-        case downward:
-            if (sbit_)
-            {
-                if (digits_ > 0 || xbit_)
-                    return 1;
-            }
-            return -1;
-        case upward:
-            if (sbit_)
-                return -1;
+        if (sbit_)
+        {
             if (digits_ > 0 || xbit_)
                 return 1;
-            return -1;
+        }
+        return -1;
     }
+
+    if (mode == upward)
+    {
+        if (sbit_)
+            return -1;
+        if (digits_ > 0 || xbit_)
+            return 1;
+        return -1;
+    }
+
+    // assume round to nearest if mode is not one of the predefined values
+    if (digits_ > 0x5000'0000'0000'0000)
+        return 1;
+    if (digits_ < 0x5000'0000'0000'0000)
+        return -1;
+    if (xbit_)
+        return 1;
+    return 0;
 }
 
 // Number
@@ -173,9 +176,9 @@ Number::normalize()
         return;
     }
     bool const negative = (mantissa_ < 0);
-    if (negative)
-        mantissa_ = -mantissa_;
     auto m = static_cast<std::make_unsigned_t<rep>>(mantissa_);
+    if (negative)
+        m = -m;
     while ((m < minMantissa) && (exponent_ > minExponent))
     {
         m *= 10;