Optimize json and msgpack hot paths

core/include/join/utils.hpp

@@ -34,6 +34,7 @@
 #include <iostream>
 #include <iomanip>
 #include <sstream>
+#include <utility>
 #include <chrono>
 #include <random>
 #include <limits>
@@ -66,6 +67,16 @@ namespace join
         };
     }
 
+    /**
+     * @brief throw an exception out of the hot path.
+     * @param args exception constructor arguments.
+     */
+    template <typename Exception, typename... Args>
+    [[noreturn]] __attribute__ ((cold, noinline)) void throwException (Args&&... args)
+    {
+        throw Exception (std::forward<Args> (args)...);
+    }
+
     /**
      * @brief swaps byte orders.
      * @param val value to swap.

core/include/join/variant.hpp

@@ -27,6 +27,7 @@
 
 // libjoin.
 #include <join/traits.hpp>
+#include <join/utils.hpp>
 
 // C++.
 #include <algorithm>
@@ -36,6 +37,7 @@
 
 // C.
 #include <cstddef>
+#include <cstdint>
 
 namespace join
 {
@@ -505,7 +507,7 @@ namespace join
         {
             if (index () != find_index_v<T, Ts...>)
             {
-                throw std::bad_cast ();
+                throwException<std::bad_cast> ();
             }
             return *reinterpret_cast<T*> (storage ());
         }
@@ -520,7 +522,7 @@ namespace join
         {
             if (index () != find_index_v<T, Ts...>)
             {
-                throw std::bad_cast ();
+                throwException<std::bad_cast> ();
             }
             return *reinterpret_cast<const T*> (storage ());
         }
@@ -535,7 +537,7 @@ namespace join
         {
             if (index () != I)
             {
-                throw std::bad_cast ();
+                throwException<std::bad_cast> ();
             }
             return *reinterpret_cast<std::tuple_element_t<I, std::tuple<Ts...>>*> (storage ());
         }
@@ -550,7 +552,7 @@ namespace join
         {
             if (index () != I)
             {
-                throw std::bad_cast ();
+                throwException<std::bad_cast> ();
             }
             return *reinterpret_cast<const std::tuple_element_t<I, std::tuple<Ts...>>*> (storage ());
         }
@@ -621,6 +623,10 @@ namespace join
          */
         constexpr std::size_t index () const noexcept
         {
+            if (_which >= sizeof...(Ts))
+            {
+                __builtin_unreachable ();
+            }
             return _which;
         }
 
@@ -710,7 +716,7 @@ namespace join
         alignas (Ts...) unsigned char _data[std::max ({sizeof (Ts)...})];
 
         /// index of the alternative that is currently held by the variant.
-        std::size_t _which = 0;
+        uint32_t _which = 0;
     };
 
     /**

core/tests/utils_test.cpp

@@ -29,6 +29,7 @@
 #include <gtest/gtest.h>
 
 // C++.
+#include <typeinfo>
 #include <sstream>
 #include <thread>
 
@@ -365,6 +366,15 @@ TEST (Utils, nextPow2)
     static_assert (join::isPow2 (join::nextPow2 (300)), "nextPow2 must yield a power of two");
 }
 
+/**
+ * @brief test throwException.
+ */
+TEST (Utils, throwException)
+{
+    EXPECT_THROW (join::throwException<std::bad_cast> (), std::bad_cast);
+    EXPECT_THROW (join::throwException<std::out_of_range> ("invalid key"), std::out_of_range);
+}
+
 /**
  * @brief main function.
  */

data/include/join/document.hpp

@@ -31,6 +31,7 @@
 #include <join/sax.hpp>
 
 // C++.
+#include <string_view>
 #include <algorithm>
 #include <iterator>
 #include <utility>
@@ -215,19 +216,9 @@ namespace join
          * @param value string value to set.
          * @return 0 on success, -1 otherwise.
          */
-        int setString (const std::string& value)
+        int setString (std::string_view value)
         {
-            return emplaceValue (value);
-        }
-
-        /**
-         * @brief set string value.
-         * @param value string value to move.
-         * @return 0 on success, -1 otherwise.
-         */
-        int setString (std::string&& value)
-        {
-            return emplaceValue (std::move (value));
+            return emplaceValue (std::string (value));
         }
 
         /**

data/include/join/dtoa.hpp

@@ -71,7 +71,16 @@ namespace join
             }
             else if ((0 < kk) && (kk <= 21))
             {
-                memmove (&buffer[kk + 1], &buffer[kk], length - kk);
+                if ((length - kk <= 16) && (kk <= 7))
+                {
+                    char tmp[16];
+                    memcpy (tmp, &buffer[kk], 16);
+                    memcpy (&buffer[kk + 1], tmp, 16);
+                }
+                else
+                {
+                    memmove (&buffer[kk + 1], &buffer[kk], length - kk);
+                }
                 buffer[kk] = '.';
                 return &buffer[length + 1];
             }
@@ -170,10 +179,8 @@ namespace join
                 delta *= 10;
                 unit *= 10;
                 char d = static_cast<char> (p2 >> -one._exponent);
-                if (d || length)
-                {
-                    buffer[length++] = '0' + d;
-                }
+                buffer[length] = '0' + d;
+                length += (d || length);
                 p2 &= one._mantissa - 1;
                 --kappa;
                 if (p2 < delta)