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       1             : //==-- llvm/Support/CheckedArithmetic.h - Safe arithmetical operations *- C++ //
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This file contains generic functions for operating on integers which
      11             : // give the indication on whether the operation has overflown.
      12             : //
      13             : //===----------------------------------------------------------------------===//
      14             : 
      15             : #ifndef LLVM_SUPPORT_CHECKEDARITHMETIC_H
      16             : #define LLVM_SUPPORT_CHECKEDARITHMETIC_H
      17             : 
      18             : #include "llvm/ADT/APInt.h"
      19             : #include "llvm/ADT/Optional.h"
      20             : 
      21             : #include <type_traits>
      22             : 
      23             : namespace {
      24             : 
      25             : /// Utility function to apply a given method of \c APInt \p F to \p LHS and
      26             : /// \p RHS.
      27             : /// \return Empty optional if the operation overflows, or result otherwise.
      28             : template <typename T, typename F>
      29             : typename std::enable_if<std::is_integral<T>::value && sizeof(T) * 8 <= 64,
      30             :                         llvm::Optional<T>>::type
      31        3722 : checkedOp(T LHS, T RHS, F Op, bool Signed = true) {
      32        3710 :   llvm::APInt ALHS(/*BitSize=*/sizeof(T) * 8, LHS, Signed);
      33        3710 :   llvm::APInt ARHS(/*BitSize=*/sizeof(T) * 8, RHS, Signed);
      34             :   bool Overflow;
      35        3722 :   llvm::APInt Out = (ALHS.*Op)(ARHS, Overflow);
      36        3722 :   if (Overflow)
      37             :     return llvm::None;
      38        3699 :   return Signed ? Out.getSExtValue() : Out.getZExtValue();
      39             : }
      40          12 : }
      41             : 
      42             : namespace llvm {
      43             : 
      44          12 : /// Add two signed integers \p LHS and \p RHS.
      45          12 : /// \return Optional of sum if no signed overflow occurred,
      46             : /// \c None otherwise.
      47           6 : template <typename T>
      48             : typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
      49          16 : checkedAdd(T LHS, T RHS) {
      50        1852 :   return checkedOp(LHS, RHS, &llvm::APInt::sadd_ov);
      51          16 : }
      52             : 
      53          16 : /// Multiply two signed integers \p LHS and \p RHS.
      54          16 : /// \return Optional of product if no signed overflow occurred,
      55             : /// \c None otherwise.
      56          14 : template <typename T>
      57             : typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
      58          16 : checkedMul(T LHS, T RHS) {
      59        1858 :   return checkedOp(LHS, RHS, &llvm::APInt::smul_ov);
      60          16 : }
      61             : 
      62          16 : /// Multiply A and B, and add C to the resulting product.
      63          16 : /// \return Optional of result if no signed overflow occurred,
      64             : /// \c None otherwise.
      65           7 : template <typename T>
      66             : typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
      67        1842 : checkedMulAdd(T A, T B, T C) {
      68        1842 :   if (auto Product = checkedMul(A, B))
      69        1836 :     return checkedAdd(*Product, C);
      70             :   return llvm::None;
      71             : }
      72             : 
      73             : /// Add two unsigned integers \p LHS and \p RHS.
      74             : /// \return Optional of sum if no unsigned overflow occurred,
      75             : /// \c None otherwise.
      76             : template <typename T>
      77           8 : typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
      78             : checkedAddUnsigned(T LHS, T RHS) {
      79             :   return checkedOp(LHS, RHS, &llvm::APInt::uadd_ov, /*Signed=*/false);
      80             : }
      81             : 
      82             : /// Multiply two unsigned integers \p LHS and \p RHS.
      83             : /// \return Optional of product if no unsigned overflow occurred,
      84             : /// \c None otherwise.
      85             : template <typename T>
      86           8 : typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
      87             : checkedMulUnsigned(T LHS, T RHS) {
      88             :   return checkedOp(LHS, RHS, &llvm::APInt::umul_ov, /*Signed=*/false);
      89             : }
      90             : 
      91             : /// Multiply unsigned integers A and B, and add C to the resulting product.
      92             : /// \return Optional of result if no unsigned overflow occurred,
      93             : /// \c None otherwise.
      94           8 : template <typename T>
      95           8 : typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
      96           8 : checkedMulAddUnsigned(T A, T B, T C) {
      97             :   if (auto Product = checkedMulUnsigned(A, B))
      98             :     return checkedAddUnsigned(*Product, C);
      99           4 :   return llvm::None;
     100           4 : }
     101           4 : 
     102             : } // End llvm namespace
     103             : 
     104           4 : #endif