From 93d2ad6bd0161ee577b49de463b5e1d65ea6f92e Mon Sep 17 00:00:00 2001
From: King_DuckZ <king_duckz@gmx.com>
Date: Thu, 22 Apr 2021 13:02:51 +0200
Subject: [PATCH] Make ary_to_int() constexpr

---
 CMakeLists.txt                        |  2 +-
 include/duckhandy/implem/int_conv.hpp | 22 +++++++++++++---------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 43607b7..0621e5e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,7 +27,7 @@ target_compile_features(${PROJECT_NAME}
 	INTERFACE cxx_decltype_incomplete_return_types
 	INTERFACE cxx_noexcept
 	INTERFACE cxx_rvalue_references
-	INTERFACE cxx_std_17
+	INTERFACE cxx_std_20
 )
 
 target_include_directories(${PROJECT_NAME}
diff --git a/include/duckhandy/implem/int_conv.hpp b/include/duckhandy/implem/int_conv.hpp
index db9aa20..9d941c6 100644
--- a/include/duckhandy/implem/int_conv.hpp
+++ b/include/duckhandy/implem/int_conv.hpp
@@ -33,6 +33,7 @@
 #	include <string_view>
 #	include <string>
 #endif
+#include <type_traits>
 
 namespace dhandy {
 	namespace implem {
@@ -168,15 +169,15 @@ namespace dhandy {
 
 		template <typename T>
 		[[gnu::always_inline,gnu::pure]]
-		inline T negated_ifn (T n, bool negate) {
+		constexpr inline T negated_ifn (T n, bool negate) {
 			//return static_cast<int32_t>(((static_cast<unsigned int>(n) - (mask bitand 1)) xor mask) bitor ((mask bitand 1) << 31));
 			return (negate ? -n : n);
 		}
 
-		template <typename I, unsigned int Base, typename Tr, typename=void>
+		template <typename I, unsigned int Base, typename Tr, bool Constexpr, typename=void>
 		struct AryConversion {
 			template <typename C>
-			static I from_ary (const C* beg, const C* end) {
+			constexpr static I from_ary (const C* beg, const C* end) {
 				I retval = 0;
 				I factor = 1;
 				std::size_t i = end - beg;
@@ -195,13 +196,13 @@ namespace dhandy {
 		};
 
 		template <typename I, unsigned int Base, typename Tr>
-		struct AryConversion<I, Base, Tr, typename std::enable_if<Tr::BehavesLikeASCII and std::is_integral<I>::value and not std::is_same<I, bool>::value and sizeof(I) <= sizeof(uint32_t)>::type> {
+		struct AryConversion<I, Base, Tr, false, typename std::enable_if<Tr::BehavesLikeASCII and std::is_integral<I>::value and not std::is_same<I, bool>::value and sizeof(I) <= sizeof(uint32_t)>::type> {
 			template <typename C> static I from_ary (C* beg, C* end) { return to_integer_sse<I, C, Base, Tr>(beg, end - beg); }
 		};
 
-		template <unsigned int Base, typename Tr>
-		struct AryConversion<bool, Base, Tr, void> {
-			template <typename C> static bool from_ary (C* beg, C* end) {
+		template <unsigned int Base, typename Tr, bool Constexpr>
+		struct AryConversion<bool, Base, Tr, Constexpr> {
+			template <typename C> constexpr static bool from_ary (C* beg, C* end) {
 				if (end == beg)
 					return false;
 				return (Tr::from_digit(*beg) ? true : false);
@@ -291,8 +292,11 @@ namespace dhandy {
 	}
 
 	template <typename R, typename C, unsigned int Base=10, typename Tr=ASCIITranslator<C>>
-	inline R ary_to_int (const C* beg, const C* end) {
-		return implem::AryConversion<R, Base, Tr>::from_ary(beg, end);
+	constexpr inline R ary_to_int (const C* beg, const C* end) {
+		if (std::is_constant_evaluated())
+			return implem::AryConversion<R, Base, Tr, true>::from_ary(beg, end);
+		else
+			return implem::AryConversion<R, Base, Tr, false>::from_ary(beg, end);
 	}
 
 #if !defined(INT_CONV_WITHOUT_HELPERS)