Make to_string work with __float128

include/fmt/format-inl.h

@@ -128,12 +128,6 @@ FMT_FUNC std::system_error vsystem_error(int error_code, string_view format_str,
 
 namespace detail {
 
-#if __cplusplus < 201703L
-template <typename T> constexpr uint64_t basic_data<T>::pow10_significands[];
-template <typename T> constexpr int16_t basic_data<T>::pow10_exponents[];
-template <typename T> constexpr uint64_t basic_data<T>::power_of_10_64[];
-#endif
-
 template <typename F> inline bool operator==(basic_fp<F> x, basic_fp<F> y) {
   return x.f == y.f && x.e == y.e;
 }

include/fmt/format.h

@@ -1511,6 +1511,12 @@ template <typename T = void> struct basic_data {
       10000000000000000000ULL};
 };
 
+#if __cplusplus < 201703L
+template <typename T> constexpr uint64_t basic_data<T>::pow10_significands[];
+template <typename T> constexpr int16_t basic_data<T>::pow10_exponents[];
+template <typename T> constexpr uint64_t basic_data<T>::power_of_10_64[];
+#endif
+
 // This is a struct rather than an alias to avoid shadowing warnings in gcc.
 struct data : basic_data<> {};
 

test/format-test.cc

@@ -1982,6 +1982,10 @@ TEST(format_test, to_string) {
 
   enum foo : unsigned char { zero };
   EXPECT_EQ(fmt::to_string(zero), "0");
+
+#if FMT_USE_FLOAT128
+  EXPECT_EQ(fmt::to_string(__float128(0.42)), "0.42");
+#endif
 }
 
 TEST(format_test, output_iterators) {