Make the Relational tests way more comprehensive

- Test combinatorically with a large variety of values.

include/xrpl/basics/Number.h

@@ -408,33 +408,38 @@ public:
     }
 
     friend constexpr bool
-    operator<(Number const& x, Number const& y) noexcept
+    operator<(Number const& l, Number const& r) noexcept
     {
+        bool const lneg = l.negative_;
+        bool const rneg = r.negative_;
+
         // If the two amounts have different signs (zero is treated as positive)
         // then the comparison is true iff the left is negative.
-        bool const lneg = x.negative_;
-        bool const rneg = y.negative_;
-
         if (lneg != rneg)
             return lneg;
 
-        // Both have same sign and the left is zero: the right must be
-        // greater than 0.
-        if (x.mantissa_ == 0)
-            return y.mantissa_ > 0;
+        // Both have same sign and the left is zero: both must be non-negative.
+        // If the right is greater than 0, then it is larger, so the comparison is true.
+        if (l.mantissa_ == 0)
+            return r.mantissa_ > 0;
 
-        // Both have same sign, the right is zero and the left is non-zero.
-        if (y.mantissa_ == 0)
+        // Both have same sign, the right is zero and the left is non-zero, so the left must be
+        // positive, and thus is larger, so the comparison is false.
+        if (r.mantissa_ == 0)
             return false;
 
         // Both have the same sign, compare by exponents:
-        if (x.exponent_ > y.exponent_)
+        if (l.exponent_ > r.exponent_)
             return lneg;
-        if (x.exponent_ < y.exponent_)
+        if (l.exponent_ < r.exponent_)
             return !lneg;
 
-        // If equal exponents, compare mantissas
-        return x.mantissa_ < y.mantissa_;
+        // If equal signs and exponents, compare mantissas.
+        if (lneg)
+            // If negative, the operator is reversed.
+            return l.mantissa_ > r.mantissa_;
+
+        return l.mantissa_ < r.mantissa_;
     }
 
     /** Return the sign of the amount */

src/test/basics/Number_test.cpp

@@ -10,6 +10,7 @@
 #include <boost/multiprecision/cpp_dec_float.hpp>
 #include <boost/multiprecision/number.hpp>
 
+#include <algorithm>
 #include <array>
 #include <cctype>
 #include <cstdint>
@@ -20,6 +21,7 @@
 #include <stdexcept>
 #include <string>
 #include <tuple>
+#include <utility>
 
 namespace xrpl {
 
@@ -1386,10 +1388,91 @@ public:
     testRelationals()
     {
         testcase << "test_relationals " << to_string(Number::getMantissaScale());
-        BEAST_EXPECT(!(Number{100} < Number{10}));
-        BEAST_EXPECT(Number{100} > Number{10});
-        BEAST_EXPECT(Number{100} >= Number{10});
-        BEAST_EXPECT(!(Number{100} <= Number{10}));
+
+        {
+            auto const nums = [this]() {
+                // Inequality test cases are built from a list of sorted integers
+                auto const values =
+                    std::to_array<int>({-100, -50, -20, -10, -1, 0, 1, 10, 20, 50, 100});
+                BEAST_EXPECT(std::ranges::is_sorted(values));
+
+                std::vector<Number> result;
+                result.reserve(values.size() + 1);
+                result.emplace_back(-1, 100);
+                for (auto const v : values)
+                {
+                    if (v == 0)
+                        result.emplace_back(-2, -10);
+                    result.emplace_back(v);
+                    if (v == 0)
+                        result.emplace_back(2, -10);
+                }
+                result.emplace_back(1, 100);
+                return result;
+            }();
+
+            BEAST_EXPECT(std::ranges::is_sorted(nums));
+
+            for (auto iter1 = nums.begin(); iter1 != nums.end(); ++iter1)
+            {
+                auto iter2 = iter1;
+                for (++iter2; iter2 != nums.end(); ++iter2)
+                {
+                    Number const& smaller = *iter1;
+                    Number const& larger = *iter2;
+                    std::stringstream ss;
+                    ss << smaller << " < " << larger;
+                    auto const str = ss.str();
+
+                    // The ==/!= operators use a completely different code path than <, etc.
+                    // This helps detect a breakage in one but not the other. It also helps
+                    // verify that the values are being ordered correctly.
+                    BEAST_EXPECTS(smaller != larger, str + " (!=)");
+                    BEAST_EXPECTS(!(smaller == larger), str + " (==)");
+
+                    // true results using operator< and derived operators
+                    BEAST_EXPECTS(smaller < larger, str + " (<)");
+                    BEAST_EXPECTS(larger > smaller, str + " (>)");
+                    BEAST_EXPECTS(larger >= smaller, str + " (>=)");
+                    BEAST_EXPECTS(smaller <= larger, str + " (<=)");
+
+                    // false results using operator< and derived operators
+                    BEAST_EXPECTS(!(larger < smaller), str + " (! <)");
+                    BEAST_EXPECTS(!(smaller > larger), str + " (! >)");
+                    BEAST_EXPECTS(!(smaller >= larger), str + " (! >=)");
+                    BEAST_EXPECTS(!(larger <= smaller), str + " (! <=)");
+                }
+            }
+        }
+
+        {
+            // Equality test cases are <Number, __LINE__>. Number will be compared against itself
+            using Case = std::pair<Number, int>;
+            auto const c = std::to_array<Case>({
+                {700, __LINE__},
+                {50, __LINE__},
+                {1, __LINE__},
+                {0, __LINE__},
+                {-1, __LINE__},
+                {-30, __LINE__},
+                {-600, __LINE__},
+            });
+            for (auto const& [n, line] : c)
+            {
+                auto const str = to_string(n);
+
+                // NOLINTBEGIN(misc-redundant-expression) Explicitly testing operators with
+                // equivalent values
+                expect(n == n, str + " ==", __FILE__, line);
+                expect(!(n != n), str + " !=", __FILE__, line);
+
+                expect(!(n < n), str + " < ", __FILE__, line);
+                expect(!(n > n), str + " >", __FILE__, line);
+                expect(n >= n, str + " >=", __FILE__, line);
+                expect(n <= n, str + " <=", __FILE__, line);
+                // NOLINTEND(misc-redundant-expression)
+            }
+        }
     }
 
     void