1 //==-- llvm/Support/CheckedArithmetic.h - Safe arithmetical operations *- C++ //
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file contains generic functions for operating on integers which
10 // give the indication on whether the operation has overflown.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #ifndef LLVM_SUPPORT_CHECKEDARITHMETIC_H
15 #define LLVM_SUPPORT_CHECKEDARITHMETIC_H
16
17 #include "llvm/ADT/APInt.h"
18 #include "llvm/ADT/Optional.h"
19
20 #include <type_traits>
21
22 namespace {
23
24 /// Utility function to apply a given method of \c APInt \p F to \p LHS and
25 /// \p RHS.
26 /// \return Empty optional if the operation overflows, or result otherwise.
27 template <typename T, typename F>
28 typename std::enable_if<std::is_integral<T>::value && sizeof(T) * 8 <= 64,
29 llvm::Optional<T>>::type
30 checkedOp(T LHS, T RHS, F Op, bool Signed = true) {
31 llvm::APInt ALHS(/*BitSize=*/sizeof(T) * 8, LHS, Signed);
32 llvm::APInt ARHS(/*BitSize=*/sizeof(T) * 8, RHS, Signed);
33 bool Overflow;
34 llvm::APInt Out = (ALHS.*Op)(ARHS, Overflow);
35 if (Overflow)
36 return llvm::None;
37 return Signed ? Out.getSExtValue() : Out.getZExtValue();
38 }
39 }
40
41 namespace llvm {
42
43 /// Add two signed integers \p LHS and \p RHS.
44 /// \return Optional of sum if no signed overflow occurred,
45 /// \c None otherwise.
46 template <typename T>
47 typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
checkedAdd(T LHS,T RHS)48 checkedAdd(T LHS, T RHS) {
49 return checkedOp(LHS, RHS, &llvm::APInt::sadd_ov);
50 }
51
52 /// Subtract two signed integers \p LHS and \p RHS.
53 /// \return Optional of sum if no signed overflow occurred,
54 /// \c None otherwise.
55 template <typename T>
56 typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
checkedSub(T LHS,T RHS)57 checkedSub(T LHS, T RHS) {
58 return checkedOp(LHS, RHS, &llvm::APInt::ssub_ov);
59 }
60
61 /// Multiply two signed integers \p LHS and \p RHS.
62 /// \return Optional of product if no signed overflow occurred,
63 /// \c None otherwise.
64 template <typename T>
65 typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
checkedMul(T LHS,T RHS)66 checkedMul(T LHS, T RHS) {
67 return checkedOp(LHS, RHS, &llvm::APInt::smul_ov);
68 }
69
70 /// Multiply A and B, and add C to the resulting product.
71 /// \return Optional of result if no signed overflow occurred,
72 /// \c None otherwise.
73 template <typename T>
74 typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
checkedMulAdd(T A,T B,T C)75 checkedMulAdd(T A, T B, T C) {
76 if (auto Product = checkedMul(A, B))
77 return checkedAdd(*Product, C);
78 return llvm::None;
79 }
80
81 /// Add two unsigned integers \p LHS and \p RHS.
82 /// \return Optional of sum if no unsigned overflow occurred,
83 /// \c None otherwise.
84 template <typename T>
85 typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
checkedAddUnsigned(T LHS,T RHS)86 checkedAddUnsigned(T LHS, T RHS) {
87 return checkedOp(LHS, RHS, &llvm::APInt::uadd_ov, /*Signed=*/false);
88 }
89
90 /// Multiply two unsigned integers \p LHS and \p RHS.
91 /// \return Optional of product if no unsigned overflow occurred,
92 /// \c None otherwise.
93 template <typename T>
94 typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
checkedMulUnsigned(T LHS,T RHS)95 checkedMulUnsigned(T LHS, T RHS) {
96 return checkedOp(LHS, RHS, &llvm::APInt::umul_ov, /*Signed=*/false);
97 }
98
99 /// Multiply unsigned integers A and B, and add C to the resulting product.
100 /// \return Optional of result if no unsigned overflow occurred,
101 /// \c None otherwise.
102 template <typename T>
103 typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
checkedMulAddUnsigned(T A,T B,T C)104 checkedMulAddUnsigned(T A, T B, T C) {
105 if (auto Product = checkedMulUnsigned(A, B))
106 return checkedAddUnsigned(*Product, C);
107 return llvm::None;
108 }
109
110 } // End llvm namespace
111
112 #endif
113