Create a round trip fuzzer for FloatToBFloat16 and BFloat16ToFloat.

PiperOrigin-RevId: 350163764
Change-Id: I1228ab9eef664d1c2aae0d981307644e8fcdb3ef

tensorflow/core/framework/BUILD

@@ -623,7 +623,10 @@ cc_library(
     name = "bfloat16",
     srcs = ["bfloat16.cc"],
     hdrs = ["bfloat16.h"],
-    visibility = ["//tensorflow/core:__subpackages__"],
+    visibility = [
+        "//tensorflow/core:__subpackages__",
+        "//tensorflow/security/fuzzing:__subpackages__",
+    ],
     deps = [
         ":numeric_types",
         "//tensorflow/core/platform:byte_order",

tensorflow/security/fuzzing/BUILD

@@ -27,6 +27,16 @@ tf_fuzz_target(
     ],
 )
 
+tf_fuzz_target(
+    name = "bfloat16_fuzz",
+    srcs = ["bfloat16_fuzz.cc"],
+    deps = [
+        "//tensorflow/core:test",
+        "//tensorflow/core/framework:bfloat16",
+        "@com_google_absl//absl/strings",
+    ],
+)
+
 tf_fuzz_target(
     name = "AreAttrValuesEqual_fuzz",
     srcs = ["AreAttrValuesEqual_fuzz.cc"],

tensorflow/security/fuzzing/bfloat16_fuzz.cc

@@ -0,0 +1,54 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+#include <fuzzer/FuzzedDataProvider.h>
+
+#include <cstdint>
+#include <cstdlib>
+
+#include "tensorflow/core/framework/bfloat16.h"
+#include "tensorflow/core/platform/test.h"
+
+// This is a fuzzer for tensorflow::FloatToBFloat16 and
+// tensorflow::BFloat16ToFloat.
+
+namespace {
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  FuzzedDataProvider fuzzed_data(data, size);
+
+  const int array_size = 100;
+
+  float float_originals[array_size];
+  for (int i = 0; i < array_size; ++i) {
+    float_originals[i] = fuzzed_data.ConsumeFloatingPointInRange(1.0f, 1000.0f);
+  }
+  tensorflow::bfloat16 bfloats[array_size];
+  float floats_converted[array_size];
+
+  tensorflow::FloatToBFloat16(float_originals, bfloats, array_size);
+  tensorflow::BFloat16ToFloat(bfloats, floats_converted, array_size);
+
+  for (int i = 0; i < array_size; ++i) {
+    // The relative error should be less than 1/(2^7) since bfloat16
+    // has 7 bits mantissa.
+    // Copied this logic from bfloat16_test.cc
+    assert(fabs(floats_converted[i] - float_originals[i]) / float_originals[i] <
+           1.0 / 128);
+  }
+
+  return 0;
+}
+
+}  // namespace