add print support to float16 (#9960)

Author: kexinzhao

paddle/fluid/platform/float16.h

@@ -873,6 +873,11 @@ HOSTDEVICE inline bool(isfinite)(const float16& a) {
   return !((isnan)(a)) && !((isinf)(a));
 }
 
+inline std::ostream& operator<<(std::ostream& os, const float16& a) {
+  os << static_cast<float>(a);
+  return os;
+}
+
 }  // namespace platform
 }  // namespace paddle
 

paddle/fluid/platform/float16_test.cc

@@ -141,5 +141,10 @@ TEST(float16, lod_tensor_cpu) {
   }
 }
 
+TEST(float16, print) {
+  float16 a = float16(1.0f);
+  std::cout << a << std::endl;
+}
+
 }  // namespace platform
 }  // namespace paddle