1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_RUNTIME_INTERPRETER_SAFE_MATH_H_
18#define ART_RUNTIME_INTERPRETER_SAFE_MATH_H_
19
20#include <functional>
21#include <type_traits>
22
23namespace art {
24namespace interpreter {
25
26// Declares a type which is the larger in bit size of the two template parameters.
27template <typename T1, typename T2>
28struct select_bigger {
29  typedef typename std::conditional<sizeof(T1) >= sizeof(T2), T1, T2>::type type;
30};
31
32// Perform signed arithmetic Op on 'a' and 'b' with defined wrapping behavior.
33template<template <typename OpT> class Op, typename T1, typename T2>
34static inline typename select_bigger<T1, T2>::type SafeMath(T1 a, T2 b) {
35  typedef typename select_bigger<T1, T2>::type biggest_T;
36  typedef typename std::make_unsigned<biggest_T>::type unsigned_biggest_T;
37  static_assert(std::is_signed<T1>::value, "Expected T1 to be signed");
38  static_assert(std::is_signed<T2>::value, "Expected T2 to be signed");
39  unsigned_biggest_T val1 = static_cast<unsigned_biggest_T>(static_cast<biggest_T>(a));
40  unsigned_biggest_T val2 = static_cast<unsigned_biggest_T>(b);
41  return static_cast<biggest_T>(Op<unsigned_biggest_T>()(val1, val2));
42}
43
44// Perform signed a signed add on 'a' and 'b' with defined wrapping behavior.
45template<typename T1, typename T2>
46static inline typename select_bigger<T1, T2>::type SafeAdd(T1 a, T2 b) {
47  return SafeMath<std::plus>(a, b);
48}
49
50// Perform signed a signed substract on 'a' and 'b' with defined wrapping behavior.
51template<typename T1, typename T2>
52static inline typename select_bigger<T1, T2>::type SafeSub(T1 a, T2 b) {
53  return SafeMath<std::minus>(a, b);
54}
55
56// Perform signed a signed multiply on 'a' and 'b' with defined wrapping behavior.
57template<typename T1, typename T2>
58static inline typename select_bigger<T1, T2>::type SafeMul(T1 a, T2 b) {
59  return SafeMath<std::multiplies>(a, b);
60}
61
62}  // namespace interpreter
63}  // namespace art
64
65#endif  // ART_RUNTIME_INTERPRETER_SAFE_MATH_H_
66