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
22namespace {
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.
27template <typename T, typename F>
28typename std::enable_if<std::is_integral<T>::value && sizeof(T) * 8 <= 64,
29                        llvm::Optional<T>>::type
30checkedOp(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
41namespace 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.
46template <typename T>
47typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
48checkedAdd(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.
55template <typename T>
56typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
57checkedSub(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.
64template <typename T>
65typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
66checkedMul(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.
73template <typename T>
74typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
75checkedMulAdd(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.
84template <typename T>
85typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
86checkedAddUnsigned(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.
93template <typename T>
94typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
95checkedMulUnsigned(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.
102template <typename T>
103typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
104checkedMulAddUnsigned(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