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[safe_op] Refactored addition overflow checks using functions only

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- templated structs were not required, SFINAE works for functions too
  => use instead, removes some unneeded code
- fix non-usage of builtins with clang
- adjust unit tests
v0.27.3
Dan Čermák 7 years ago
parent 684c8c89de
commit 06ec1e6984
2 changed files with 109 additions and 148 deletions
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253
src/safe_op.hpp
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@ -42,33 +42,32 @@
namespace Safe
{
/*!
* @brief Helper structs for providing integer overflow checks.
* @brief Helper functions for providing integer overflow checks.
*
* This namespace contains the internal helper structs fallback_add_overflow
* and builtin_add_overflow. Both have a public static member function add
* with the following interface:
* This namespace contains internal helper functions fallback_$op_overflow
* and builtin_$op_overflow (where $op is an arithmetic operation like add,
* subtract, etc.). Both provide the following interface:
*
* bool add(T summand_1, T summand_2, T& result)
* bool fallback/builtin_$op_overflow(T first, T second, T& result);
*
* where T is the type over which the struct is templated.
* where T is an integer type.
*
* The function performs a check whether the addition summand_1 + summand_2
* can be performed without an overflow. If the operation would overflow,
* true is returned and the addition is not performed if it would result in
* undefined behavior. If no overflow occurs, the sum is saved in result and
* false is returned.
* Each function performs checks whether first $op second can be safely
* performed without overflows. If yes, the result is saved in result and
* false is returned. Otherwise true is returned and the contents of result
* are unspecified.
*
* fallback_add_overflow implements a portable but slower overflow check.
* builtin_add_overflow uses compiler builtins (when available) and should
* be considerably faster. As builtins are not available for all types,
* builtin_add_overflow falls back to fallback_add_overflow when no builtin
* fallback_$op_overflow implements a portable but slower overflow check.
* builtin_$op_overflow uses compiler builtins (when available) and should
* be faster. As builtins are not available for all types,
* builtin_$op_overflow falls back to fallback_$op_overflow when no builtin
* is available.
*/
namespace Internal
{
/*!
* @brief Helper struct to determine whether a type is signed or unsigned
*
* This struct is a backport of std::is_signed from C++11. It has a public
* enum with the property VALUE which is true when the type is signed or
* false if it is unsigned.
@ -103,145 +102,111 @@ namespace Safe
};
/*!
* @brief Fallback overflow checker, specialized via SFINAE
* @brief Check the addition of two numbers for overflows for signed
* integer types larger than int or with the same size as int.
*
* This struct implements a 'fallback' addition with an overflow check,
* i.e. it does not rely on compiler intrinsics. It is specialized via
* SFINAE for signed and unsigned integer types and provides a public
* static member function add.
*/
template <typename T, typename = void>
struct fallback_add_overflow;
/*!
* @brief Overload of fallback_add_overflow for signed integer types
* larger then int or with the same size as int
* This function performs a check if summand_1 + summand_2 would
* overflow and returns true in that case. If no overflow occurs,
* the sum is saved in result and false is returned.
*
* @return true on overflow, false on no overflow
*
* @param[in] summand_1, summand_2 The summands with are added
* @param[out] result Result of the addition, only populated when no
* overflow occurs.
*
* Further information:
* https://wiki.sei.cmu.edu/confluence/display/c/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow
*/
template <typename T>
struct fallback_add_overflow<T, typename enable_if<is_signed<T>::VALUE && sizeof(T) >= sizeof(int)>::type>
typename enable_if<is_signed<T>::VALUE && sizeof(T) >= sizeof(int), bool>::type fallback_add_overflow(
T summand_1, T summand_2, T& result)
{
/*!
* @brief Adds the two summands only if no overflow occurs
*
* This function performs a check if summand_1 + summand_2 would
* overflow and returns true in that case. If no overflow occurs,
* the sum is saved in result and false is returned.
*
* @return true on overflow, false on no overflow
*
* The check for an overflow is performed before the addition to
* ensure that no undefined behavior occurs. The value in result is
* only valid when the function returns false.
*
* Further information:
* https://wiki.sei.cmu.edu/confluence/display/c/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow
*/
static bool add(T summand_1, T summand_2, T& result)
{
if (((summand_2 >= 0) && (summand_1 > std::numeric_limits<T>::max() - summand_2)) ||
((summand_2 < 0) && (summand_1 < std::numeric_limits<T>::min() - summand_2))) {
return true;
} else {
result = summand_1 + summand_2;
return false;
}
if (((summand_2 >= 0) && (summand_1 > std::numeric_limits<T>::max() - summand_2)) ||
((summand_2 < 0) && (summand_1 < std::numeric_limits<T>::min() - summand_2))) {
return true;
} else {
result = summand_1 + summand_2;
return false;
}
};
}
/*!
* @brief Overload of fallback_add_overflow for signed integers smaller
* then int.
* @brief Check the addition of two numbers for overflows for signed
* integer types smaller than int.
*
* This function adds summand_1 and summand_2 exploiting integer
* promotion rules, thereby not causing undefined behavior. The
* result is checked against the limits of T and true is returned if
* they are exceeded. Otherwise the sum is saved in result and false
* is returned.
*
* @return true on overflow, false on no overflow
*
* @param[in] summand_1, summand_2 The summands with are added
* @param[out] result Result of the addition, only populated when no
* overflow occurs.
*
* Further information:
* https://wiki.sei.cmu.edu/confluence/display/c/INT02-C.+Understand+integer+conversion+rules
*/
template <typename T>
struct fallback_add_overflow<T, typename enable_if<is_signed<T>::VALUE && sizeof(T) < sizeof(int)>::type>
typename enable_if<is_signed<T>::VALUE && sizeof(T) < sizeof(int), bool>::type fallback_add_overflow(
T summand_1, T summand_2, T& result)
{
/*!
* @brief Adds the two summands only if no overflow occurs
*
* This function adds summand_1 and summand_2 exploiting integer
* promotion rules, thereby not causing undefined behavior. The
* result is checked against the limits of T and true is returned if
* they are exceeded. Otherwise the sum is saved in result and false
* is returned.
*
* @return true on overflow, false on no overflow
*
* The value in result is only valid when the function returns
* false.
*
* Further information:
* https://wiki.sei.cmu.edu/confluence/display/c/INT02-C.+Understand+integer+conversion+rules
*/
static bool add(T summand_1, T summand_2, T& result)
{
const int res = summand_1 + summand_2;
if ((res > std::numeric_limits<T>::max()) || (res < std::numeric_limits<T>::min())) {
return true;
} else {
result = static_cast<T>(res);
return false;
}
const int res = summand_1 + summand_2;
if ((res > std::numeric_limits<T>::max()) || (res < std::numeric_limits<T>::min())) {
return true;
} else {
result = static_cast<T>(res);
return false;
}
};
}
/*!
* @brief Overload of fallback_add_overflow for unsigned integers
* @brief Check the addition of two numbers for overflows for unsigned
* integer types.
*
* This function adds summand_1 and summand_2 and checks after that if
* the operation overflowed. Since these are unsigned integers, no
* undefined behavior is invoked.
*
* @return true on overflow, false on no overflow
*
* @param[in] summand_1, summand_2 The summands with are added
* @param[out] result Result of the addition
*
* Further information:
* https://wiki.sei.cmu.edu/confluence/display/c/INT30-C.+Ensure+that+unsigned+integer+operations+do+not+wrap
*/
template <typename T>
struct fallback_add_overflow<T, typename enable_if<!is_signed<T>::VALUE>::type>
typename enable_if<!is_signed<T>::VALUE, bool>::type fallback_add_overflow(T summand_1, T summand_2, T& result)
{
/*!
* @brief Adds the two summands only if no overflow occurs
*
* This function performs a check if summand_1 + summand_2 would
* overflow and returns true in that case. If no overflow occurs,
* the sum is saved in result and false is returned.
*
* @return true on overflow, false on no overflow
*
* Further information:
* https://wiki.sei.cmu.edu/confluence/display/c/INT30-C.+Ensure+that+unsigned+integer+operations+do+not+wrap
*/
static bool add(T summand_1, T summand_2, T& result)
{
result = summand_1 + summand_2;
return result < summand_1;
}
};
result = summand_1 + summand_2;
return result < summand_1;
}
/*!
* @brief Overflow checker using compiler intrinsics
* @brief Overflow addition check using compiler intrinsics.
*
* This struct provides an add function with the same interface &
* behavior as fallback_add_overload::add but it relies on compiler
* intrinsics instead. This version should be considerably faster than
* the fallback version as it can fully utilize available CPU
* This function behaves exactly like fallback_add_overflow() but it
* relies on compiler intrinsics instead. This version should be faster
* than the fallback version as it can fully utilize available CPU
* instructions & the compiler's diagnostic.
*
* However, as some compilers don't provide intrinsics for certain
* types, the default implementation of add is the version from fallback.
* types, the default implementation is the version from fallback.
*
* The struct is explicitly specialized for each type via #ifdefs for
* each compiler.
* This function is fully specialized for each compiler.
*/
template <typename T>
struct builtin_add_overflow
bool builtin_add_overflow(T summand_1, T summand_2, T& result)
{
/*!
* @brief Add summand_1 and summand_2 and check for overflows.
*
* This is the default add() function that uses
* fallback_add_overflow<T>::add(). All specializations must have
* exactly the same interface and behave the same way.
*/
static inline bool add(T summand_1, T summand_2, T& result)
{
return fallback_add_overflow<T>::add(summand_1, summand_2, result);
}
};
return fallback_add_overflow(summand_1, summand_2, result);
}
#if defined(__GNUC__) || defined(__clang__)
#if __GNUC__ >= 5
#if __GNUC__ >= 5 || __clang_major__ >= 3
/*!
* This macro pastes a specialization of builtin_add_overflow using gcc's &
@ -253,14 +218,13 @@ namespace Safe
* The intrinsics are documented here:
* https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html#Integer-Overflow-Builtins
*/
#define SPECIALIZE_builtin_add_overflow(type, builtin_name) \
template <> \
struct builtin_add_overflow<type> \
{ \
static inline bool add(type summand_1, type summand_2, type& result) \
{ \
return builtin_name(summand_1, summand_2, &result); \
} \
#define SPECIALIZE_builtin_add_overflow(type, builtin_name) \
/* Full specialization of builtin_add_overflow for type using the */ \
/* builtin_name intrinsic */ \
template <> \
bool builtin_add_overflow<type>(type summand_1, type summand_2, type & result) \
{ \
return builtin_name(summand_1, summand_2, &result); \
}
SPECIALIZE_builtin_add_overflow(int, __builtin_sadd_overflow);
@ -272,7 +236,7 @@ namespace Safe
SPECIALIZE_builtin_add_overflow(unsigned long long, __builtin_uaddll_overflow);
#undef SPECIALIZE_builtin_add_overflow
#endif
#endif // __GNUC__ >= 5 || __clang_major >= 3
#elif defined(_MSC_VER)
@ -289,14 +253,11 @@ namespace Safe
* The intrinsics are documented here:
* https://msdn.microsoft.com/en-us/library/windows/desktop/ff516460(v=vs.85).aspx
*/
#define SPECIALIZE_builtin_add_overflow_WIN(type, builtin_name) \
template <> \
struct builtin_add_overflow<type> \
{ \
static inline bool add(type summand_1, type summand_2, type& result) \
{ \
return builtin_name(summand_1, summand_2, &result) != S_OK; \
} \
#define SPECIALIZE_builtin_add_overflow_WIN(type, builtin_name) \
template <> \
bool builtin_add_overflow(type summand_1, type summand_2, type& result) \
{ \
return builtin_name(summand_1, summand_2, &result) != S_OK; \
}
SPECIALIZE_builtin_add_overflow_WIN(unsigned int, UIntAdd);
@ -305,7 +266,7 @@ namespace Safe
#undef SPECIALIZE_builtin_add_overflow_WIN
#endif
#endif // defined(_MSC_VER)
} // namespace Internal
@ -332,7 +293,7 @@ namespace Safe
T add(T summand_1, T summand_2)
{
T res = 0;
if (Internal::builtin_add_overflow<T>::add(summand_1, summand_2, res)) {
if (Internal::builtin_add_overflow(summand_1, summand_2, res)) {
throw std::overflow_error("Overflow in addition");
}
return res;

4
unitTests/test_safe_op.cpp
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@ -115,8 +115,8 @@ void test_add()
} \
}
TEST_ADD(si::fallback_add_overflow<T>::add)
TEST_ADD(si::builtin_add_overflow<T>::add)
TEST_ADD(si::fallback_add_overflow)
TEST_ADD(si::builtin_add_overflow)
#undef TEST_ADD
}

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