Add a MetaPhysicL::detail::less impl

Co-authored-by: Codex <codex@openai.com>

Author: lindsayad

src/utilities/include/metaphysicl/metaphysicl_algorithm.h

@@ -3,8 +3,37 @@
 
 #include "metaphysicl/metaphysicl_device.h"
 
+#include <type_traits>
+
 namespace MetaPhysicL::detail {
 
+template <typename T, typename U>
+METAPHYSICL_INLINE constexpr bool less(const T & lhs, const U & rhs)
+{
+  typedef typename std::remove_const<typename std::remove_reference<T>::type>::type lhs_type;
+  typedef typename std::remove_const<typename std::remove_reference<U>::type>::type rhs_type;
+
+  if constexpr (std::is_integral<lhs_type>::value && std::is_integral<rhs_type>::value)
+  {
+    if constexpr (std::is_signed<lhs_type>::value == std::is_signed<rhs_type>::value)
+      return lhs < rhs;
+    else if constexpr (std::is_signed<lhs_type>::value)
+    {
+      if (lhs < 0)
+        return true;
+      return static_cast<typename std::make_unsigned<lhs_type>::type>(lhs) < rhs;
+    }
+    else
+    {
+      if (rhs < 0)
+        return false;
+      return lhs < static_cast<typename std::make_unsigned<rhs_type>::type>(rhs);
+    }
+  }
+  else
+    return lhs < rhs;
+}
+
 template <typename ForwardIt, typename T>
 METAPHYSICL_INLINE ForwardIt lower_bound(ForwardIt first, ForwardIt last, const T & value)
 {
@@ -13,7 +42,7 @@ METAPHYSICL_INLINE ForwardIt lower_bound(ForwardIt first, ForwardIt last, const
   {
     const auto step = count / 2;
     auto it = first + step;
-    if (*it < value)
+    if (less(*it, value))
     {
       first = ++it;
       count -= step + 1;
@@ -58,7 +87,7 @@ METAPHYSICL_INLINE bool is_sorted(ForwardIt first, ForwardIt last)
     auto next = first;
     while (++next != last)
     {
-      if (*next < *first)
+      if (less(*next, *first))
         return false;
       first = next;
     }