Enable operator<< for Half (#1733)

Summary: Pull Request resolved: #1733

Reviewed By: mikekgfb

Differential Revision: D53139440

fbshipit-source-id: e371ea15516677dfc726757047f4c5fb2b793d21

Author: manuelcandales

runtime/core/exec_aten/testing_util/tensor_util.cpp

@@ -251,7 +251,7 @@ std::ostream& operator<<(std::ostream& os, const Tensor& t) {
     break;
 
   switch (t.scalar_type()) {
-    ET_FORALL_REAL_TYPES_AND(Bool, PRINT_CASE)
+    ET_FORALL_REAL_TYPES_AND2(Half, Bool, PRINT_CASE)
     default:
       ET_CHECK_MSG(
           false,

runtime/core/portable_type/half.cpp

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <executorch/runtime/core/portable_type/half.h>
+#include <ostream>
+#include <type_traits>
+
+namespace torch {
+namespace executor {
+
+static_assert(
+    std::is_standard_layout_v<torch::executor::Half>,
+    "Half must be standard layout.");
+
+std::ostream& operator<<(
+    std::ostream& out,
+    const torch::executor::Half& value) {
+  out << (float)value;
+  return out;
+}
+
+} // namespace executor
+} // namespace torch

runtime/core/portable_type/half.h

@@ -12,6 +12,7 @@
 #include <cstdint>
 #include <cstring>
 #include <limits>
+#include <ostream>
 
 #if defined(__GNUC__) || defined(__clang__)
 #if defined(__aarch64__)
@@ -673,6 +674,8 @@ inline Half operator/(int64_t a, Half b) {
 /// NOTE: we do not define comparisons directly and instead rely on the implicit
 /// conversion Half to float.
 
+std::ostream& operator<<(std::ostream& out, const Half& value);
+
 } // namespace executor
 } // namespace torch
 

runtime/core/portable_type/targets.bzl

@@ -40,6 +40,7 @@ def define_common_targets():
     # Set up a specific exported library for scalar_type to avoid circle dependency in ScalarTypeUtil.h
     runtime.cxx_library(
         name = "scalar_type",
+        srcs = ["half.cpp"],
         exported_headers = [
             "bfloat16.h",
             "complex.h",