Migrate recursive template instantiations

include/xsimd/arch/xsimd_avx512f.hpp

@@ -2258,7 +2258,7 @@ namespace xsimd
             using register_type = typename batch_bool<T, A>::register_type;
             register_type r = 0;
             unsigned shift = 0;
-            (void)std::initializer_list<register_type> { (r |= register_type(values ? 1 : 0) << (shift++))... };
+            ((r |= register_type(values ? 1 : 0) << (shift++)), ...);
             return r;
         }
 
@@ -2656,21 +2656,19 @@ namespace xsimd
 
         namespace detail
         {
-            template <class T, class A, T... Idx>
-            struct is_pair_of_contiguous_indices;
-
-            template <class T, class A>
-            struct is_pair_of_contiguous_indices<T, A> : std::true_type
+            template <class T, T... Idx, std::size_t... Is>
+            constexpr bool is_pair_of_contiguous_indices_impl(std::index_sequence<Is...>) noexcept
             {
-            };
+                constexpr T idx[] = { Idx... };
+                return (... && (idx[2 * Is] % 2 == 0 && idx[2 * Is] + 1 == idx[2 * Is + 1]));
+            }
 
-            template <class T, class A, T Idx0, T Idx1, T... Idx>
-            struct is_pair_of_contiguous_indices<T, A, Idx0, Idx1, Idx...> : std::conditional_t<(Idx0 % 2 == 0) && (Idx0 + 1 == Idx1), is_pair_of_contiguous_indices<T, A, Idx...>, std::false_type>
+            template <class T, T... Idx>
+            constexpr bool is_pair_of_contiguous_indices() noexcept
             {
-            };
-
-            template <class T, class A, T... Idx>
-            inline constexpr bool is_pair_of_contiguous_indices_v = is_pair_of_contiguous_indices<T, A, Idx...>::value;
+                static_assert(sizeof...(Idx) % 2 == 0, "indices come in pairs");
+                return is_pair_of_contiguous_indices_impl<T, Idx...>(std::make_index_sequence<sizeof...(Idx) / 2>());
+            }
 
             template <class A, uint16_t I0, uint16_t I1, uint16_t I2, uint16_t I3, uint16_t I4, uint16_t I5, uint16_t I6, uint16_t I7,
                       uint16_t I8, uint16_t I9, uint16_t I10, uint16_t I11, uint16_t I12, uint16_t I13, uint16_t I14, uint16_t I15,
@@ -2703,7 +2701,7 @@ namespace xsimd
         template <class A, uint16_t... Idx>
         XSIMD_INLINE batch<uint16_t, A> swizzle(batch<uint16_t, A> const& self, batch_constant<uint16_t, A, Idx...> mask, requires_arch<avx512f>) noexcept
         {
-            if constexpr (detail::is_pair_of_contiguous_indices_v<uint16_t, A, Idx...>)
+            if constexpr (detail::is_pair_of_contiguous_indices<uint16_t, Idx...>())
             {
                 constexpr typename detail::fold_batch_constant<A, Idx...>::type mask32;
                 return _mm512_permutexvar_epi32(static_cast<batch<uint32_t, A>>(mask32), self);

include/xsimd/arch/xsimd_avx512vl_128.hpp

@@ -176,7 +176,7 @@ namespace xsimd
             using register_type = typename batch_bool<T, A>::register_type;
             register_type r = 0;
             unsigned shift = 0;
-            (void)std::initializer_list<register_type> { (r |= register_type(values ? 1 : 0) << (shift++))... };
+            ((r |= register_type(values ? 1 : 0) << (shift++)), ...);
             return r;
         }
 

include/xsimd/arch/xsimd_avx512vl_256.hpp

@@ -176,7 +176,7 @@ namespace xsimd
             using register_type = typename batch_bool<T, A>::register_type;
             register_type r = 0;
             unsigned shift = 0;
-            (void)std::initializer_list<register_type> { (r |= register_type(values ? 1 : 0) << (shift++))... };
+            ((r |= register_type(values ? 1 : 0) << (shift++)), ...);
             return r;
         }
 

include/xsimd/config/xsimd_arch.hpp

@@ -16,7 +16,6 @@
 #include "./xsimd_config.hpp"
 #include "./xsimd_cpuid.hpp"
 
-#include <initializer_list>
 #include <type_traits>
 #include <utility>
 
@@ -40,22 +39,6 @@ namespace xsimd
 
     namespace detail
     {
-        // Checks whether T appears in Tys.
-        template <class T, class... Tys>
-        struct contains;
-
-        template <class T>
-        struct contains<T> : std::false_type
-        {
-        };
-
-        template <class T, class Ty, class... Tys>
-        struct contains<T, Ty, Tys...>
-            : std::conditional_t<std::is_same_v<Ty, T>, std::true_type,
-                                 contains<T, Tys...>>
-        {
-        };
-
         template <typename T>
         XSIMD_INLINE constexpr T max_of(T value) noexcept
         {
@@ -100,13 +83,13 @@ namespace xsimd
         template <class Arch>
         static constexpr bool contains() noexcept
         {
-            return detail::contains<Arch, Archs...>::value;
+            return (std::is_same_v<Arch, Archs> || ...);
         }
 
         template <class F>
         static XSIMD_INLINE void for_each(F&& f) noexcept
         {
-            (void)std::initializer_list<bool> { (f(Archs {}), true)... };
+            (f(Archs {}), ...);
         }
 
         static constexpr std::size_t alignment() noexcept

include/xsimd/types/xsimd_batch_constant.hpp

@@ -191,25 +191,15 @@ namespace xsimd
 
     private:
         // Build a 64-bit mask from Values... (LSB = index 0)
-        template <std::size_t I, bool... Remaining>
-        struct build_bits_helper;
-
-        template <std::size_t I>
-        struct build_bits_helper<I>
-        {
-            static constexpr uint64_t value = 0u;
-        };
-
-        template <std::size_t I, bool Current, bool... Remaining>
-        struct build_bits_helper<I, Current, Remaining...>
+        template <std::size_t... Is>
+        static constexpr uint64_t build_bits(std::index_sequence<Is...>) noexcept
         {
-            static constexpr uint64_t value = (Current ? (uint64_t(1) << I) : 0u)
-                | build_bits_helper<I + 1, Remaining...>::value;
-        };
+            return (uint64_t(0) | ... | (Values ? (uint64_t(1) << Is) : uint64_t(0)));
+        }
 
         static constexpr uint64_t bits() noexcept
         {
-            return build_bits_helper<0, Values...>::value;
+            return build_bits(std::make_index_sequence<sizeof...(Values)>());
         }
         static constexpr uint64_t low_mask(std::size_t k) noexcept
         {

include/xsimd/utils/bits.hpp

@@ -19,20 +19,13 @@ namespace xsimd
 {
     namespace utils
     {
-        template <typename I>
-        constexpr I make_bit_mask(I bit)
-        {
-            static_assert(std::is_unsigned_v<I>, "Bit operations must be done on unsigned integers");
-            assert(bit < static_cast<I>(8 * sizeof(I)));
-            return static_cast<I>(I { 1 } << bit);
-        }
-
         template <typename I, typename... Args>
         constexpr I make_bit_mask(I bit, Args... bits)
         {
-            // TODO(C++17): Use fold expression
             static_assert(std::is_unsigned_v<I>, "Bit operations must be done on unsigned integers");
-            return make_bit_mask<I>(bit) | make_bit_mask<I>(static_cast<I>(bits)...);
+            [[maybe_unused]] constexpr I bit_count = static_cast<I>(8 * sizeof(I));
+            assert(((bit < bit_count) && ... && (static_cast<I>(bits) < bit_count)));
+            return static_cast<I>(((I { 1 } << bit) | ... | (I { 1 } << static_cast<I>(bits))));
         }
 
         template <int... Bits, typename I>