include/llvm/Support/CheckedArithmetic.h

   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
  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
  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
  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
  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
  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
  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
 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