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<T>::value && sizeof(T) * 8 <= 64,
29                  std::optional<T>>
30 checkedOp(T LHS, T RHS, F Op, bool Signed = true) {
31   llvm::APInt ALHS(sizeof(T) * 8, LHS, Signed);
32   llvm::APInt ARHS(sizeof(T) * 8, RHS, Signed);
33   bool Overflow;
34   llvm::APInt Out = (ALHS.*Op)(ARHS, Overflow);
35   if (Overflow)
36     return std::nullopt;
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 std::nullopt otherwise.
46 template <typename T>
47 std::enable_if_t<std::is_signed<T>::value, std::optional<T>>
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 std::nullopt otherwise.
55 template <typename T>
56 std::enable_if_t<std::is_signed<T>::value, std::optional<T>>
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 std::nullopt otherwise.
64 template <typename T>
65 std::enable_if_t<std::is_signed<T>::value, std::optional<T>>
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 std::nullopt otherwise.
73 template <typename T>
74 std::enable_if_t<std::is_signed<T>::value, std::optional<T>>
75 checkedMulAdd(T A, T B, T C) {
76   if (auto Product = checkedMul(A, B))
77     return checkedAdd(*Product, C);
78   return std::nullopt;
79 }
80 
81 /// Add two unsigned integers \p LHS and \p RHS.
82 /// \return Optional of sum if no unsigned overflow occurred,
83 /// \c std::nullopt otherwise.
84 template <typename T>
85 std::enable_if_t<std::is_unsigned<T>::value, std::optional<T>>
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 std::nullopt otherwise.
93 template <typename T>
94 std::enable_if_t<std::is_unsigned<T>::value, std::optional<T>>
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 std::nullopt otherwise.
102 template <typename T>
103 std::enable_if_t<std::is_unsigned<T>::value, std::optional<T>>
104 checkedMulAddUnsigned(T A, T B, T C) {
105   if (auto Product = checkedMulUnsigned(A, B))
106     return checkedAddUnsigned(*Product, C);
107   return std::nullopt;
108 }
109 
110 } // End llvm namespace
111 
112 #endif
113