1/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7 http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#ifndef TENSORFLOW_CORE_UTIL_OVERFLOW_H_
17#define TENSORFLOW_CORE_UTIL_OVERFLOW_H_
18
19#include "tensorflow/core/platform/logging.h"
20#include "tensorflow/core/platform/macros.h"
21#include "tensorflow/core/platform/types.h"
22
23namespace tensorflow {
24
25// Multiply two nonnegative int64's, returning negative for overflow
26// If any of the arguments is negative, return negative too.
27inline int64_t MultiplyWithoutOverflow(const int64_t x, const int64_t y) {
28 if (TF_PREDICT_FALSE(x < 0)) return -1;
29 if (TF_PREDICT_FALSE(y < 0)) return -1;
30 if (TF_PREDICT_FALSE(x == 0)) return 0;
31
32 // Multiply in uint64 rather than int64 since signed overflow is undefined.
33 // Negative values will wrap around to large unsigned values in the casts
34 // (see section 4.7 [conv.integral] of the C++14 standard).
35 const uint64 ux = x;
36 const uint64 uy = y;
37 const uint64 uxy = ux * uy;
38
39 // Check if we overflow uint64, using a cheap check if both inputs are small
40 if (TF_PREDICT_FALSE((ux | uy) >> 32 != 0)) {
41 // Otherwise, detect overflow using a division
42 if (uxy / ux != uy) return -1;
43 }
44
45 // Cast back to signed. A negative value will signal an error.
46 return static_cast<int64_t>(uxy);
47}
48
49} // namespace tensorflow
50
51#endif // TENSORFLOW_CORE_UTIL_OVERFLOW_H_
52