Updated HalfVector to use _Float16 when available

Author: ankane

CHANGELOG.md

@@ -1,7 +1,7 @@
 ## 0.3.0 (unreleased)
 
 - Added support for libpqxx 8
-- Changed `HalfVector` to use `std::float16_t` when available
+- Changed `HalfVector` to use `std::float16_t` or `_Float16` when available
 - Dropped support for libpqxx 7
 - Dropped support for C++17
 

include/pgvector/halfvec.hpp

@@ -14,12 +14,17 @@
 
 #if __STDCPP_FLOAT16_T__
 #include <stdfloat>
+#else
+#define __STDC_WANT_IEC_60559_TYPES_EXT__
+#include <cfloat>
 #endif
 
 namespace pgvector {
 
 #if __STDCPP_FLOAT16_T__
 using Half = std::float16_t;
+#elif defined(__FLT16_MAX__)
+using Half = _Float16;
 #else
 using Half = float;
 #endif
@@ -61,7 +66,11 @@ class HalfVector {
             if (i > 0) {
                 os << ",";
             }
+#if __STDCPP_FLOAT16_T__
             os << value.value_[i];
+#else
+            os << static_cast<float>(value.value_[i]);
+#endif
         }
         os << "]";
         return os;

test/pqxx_test.cpp

@@ -179,8 +179,8 @@ void test_vector_from_string() {
 
 void test_halfvec_to_string() {
     assert_equal(pqxx::to_string(pgvector::HalfVector({1, 2, 3})), "[1,2,3]");
-#if __STDCPP_FLOAT16_T__
-    assert_equal(pqxx::to_string(pgvector::HalfVector({-1.234567890123f16})), "[-1.234375]");
+#if __STDCPP_FLOAT16_T__ || defined(__FLT16_MAX__)
+    assert_equal(pqxx::to_string(pgvector::HalfVector({static_cast<pgvector::Half>(-1.234567890123)})), "[-1.234375]");
 #else
     assert_equal(pqxx::to_string(pgvector::HalfVector({-1.234567890123})), "[-1.2345679]");
 #endif