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 
19 #include <optional>
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 std::enable_if_t<std::is_integral_v<T> && sizeof(T) * 8 <= 64, std::optional<T>>
29 checkedOp(T LHS, T RHS, F Op, bool Signed = true) {
30   llvm::APInt ALHS(sizeof(T) * 8, LHS, Signed);
31   llvm::APInt ARHS(sizeof(T) * 8, RHS, Signed);
32   bool Overflow;
33   llvm::APInt Out = (ALHS.*Op)(ARHS, Overflow);
34   if (Overflow)
35     return std::nullopt;
36   return Signed ? Out.getSExtValue() : Out.getZExtValue();
37 }
38 }
39 
40 namespace llvm {
41 
42 /// Add two signed integers \p LHS and \p RHS.
43 /// \return Optional of sum if no signed overflow occurred,
44 /// \c std::nullopt otherwise.
45 template <typename T>
46 std::enable_if_t<std::is_signed_v<T>, std::optional<T>> checkedAdd(T LHS,
47                                                                    T RHS) {
48   return checkedOp(LHS, RHS, &llvm::APInt::sadd_ov);
49 }
50 
51 /// Subtract two signed integers \p LHS and \p RHS.
52 /// \return Optional of sum if no signed overflow occurred,
53 /// \c std::nullopt otherwise.
54 template <typename T>
55 std::enable_if_t<std::is_signed_v<T>, std::optional<T>> checkedSub(T LHS,
56                                                                    T RHS) {
57   return checkedOp(LHS, RHS, &llvm::APInt::ssub_ov);
58 }
59 
60 /// Multiply two signed integers \p LHS and \p RHS.
61 /// \return Optional of product if no signed overflow occurred,
62 /// \c std::nullopt otherwise.
63 template <typename T>
64 std::enable_if_t<std::is_signed_v<T>, std::optional<T>> checkedMul(T LHS,
65                                                                    T RHS) {
66   return checkedOp(LHS, RHS, &llvm::APInt::smul_ov);
67 }
68 
69 /// Multiply A and B, and add C to the resulting product.
70 /// \return Optional of result if no signed overflow occurred,
71 /// \c std::nullopt otherwise.
72 template <typename T>
73 std::enable_if_t<std::is_signed_v<T>, std::optional<T>> checkedMulAdd(T A, T B,
74                                                                       T C) {
75   if (auto Product = checkedMul(A, B))
76     return checkedAdd(*Product, C);
77   return std::nullopt;
78 }
79 
80 /// Add two unsigned integers \p LHS and \p RHS.
81 /// \return Optional of sum if no unsigned overflow occurred,
82 /// \c std::nullopt otherwise.
83 template <typename T>
84 std::enable_if_t<std::is_unsigned_v<T>, std::optional<T>>
85 checkedAddUnsigned(T LHS, T RHS) {
86   return checkedOp(LHS, RHS, &llvm::APInt::uadd_ov, /*Signed=*/false);
87 }
88 
89 /// Multiply two unsigned integers \p LHS and \p RHS.
90 /// \return Optional of product if no unsigned overflow occurred,
91 /// \c std::nullopt otherwise.
92 template <typename T>
93 std::enable_if_t<std::is_unsigned_v<T>, std::optional<T>>
94 checkedMulUnsigned(T LHS, T RHS) {
95   return checkedOp(LHS, RHS, &llvm::APInt::umul_ov, /*Signed=*/false);
96 }
97 
98 /// Multiply unsigned integers A and B, and add C to the resulting product.
99 /// \return Optional of result if no unsigned overflow occurred,
100 /// \c std::nullopt otherwise.
101 template <typename T>
102 std::enable_if_t<std::is_unsigned_v<T>, std::optional<T>>
103 checkedMulAddUnsigned(T A, T B, T C) {
104   if (auto Product = checkedMulUnsigned(A, B))
105     return checkedAddUnsigned(*Product, C);
106   return std::nullopt;
107 }
108 
109 } // End llvm namespace
110 
111 #endif
112