3/2/2024 0 Comments Integer overflow wrap around![]() However, if you opt for divisions, 32-bits integers are more suitable (but just because you’re using divisions you won’t have top-notch performance). If you don’t have to use divisions, you will notice no performance gap between 32 bits and 64 bits. This may not surprise you, but in every case it’s the division which is the slowest. Using clang, using two different optimization levels, here are the results: I ran a few basic operations (addition, multiplication and division) on both int32_t and int64_t to see if there were any significant differences. So I recommend that, unless your integer has a hard limit and is very small, use a int64_t. Trying to over-optimize and risk integer overflow is always worse than to write safe code then use tools to pinpoint where the program must be optimized. Just note that longer integers does not always mean slower calculation, and with the full set of pointer / reference / forwarding, you don’t copy whole data structures very often.Īnd in any case, even if you are performance and/or size sensitive, always remember:įirst, be safe. Only if you work on embedded software or on processing algorithms you may care about performance or data size constraints (by “processing algorithms” I mean algorithms supposed to have top-notch performance, like in signal processing). Most of the time, you won’t care about the performance gap or the size gap between them. There is actually very few downsides in using int64_t instead of int32_t. In most case, 64-bits ints will not commit overflow, unlike their 32-bits counterparts. One very good way to prevent integer overflows is to use int64_t to implement integers. How to prevent integer overflows? Use 64-bits integers The next section will give a few practices to help you in that regard. If you ensure that no overflow can arise from the code you write, you won’t have to detect them. The best way be sure there is no overflow is to prevent overflows. Don’t put your code in a situation prone to overflows Don’t be afraid to do it, you are better safe than sorry. Sometime, detecting a potential overflow this way will requires weighty refactoring. You must put so error-handling in them to ensure no overflow will happen. ![]() If you don’t know what result to expect when you put a big int into them, because the result would be too big, and there is no error-handling, then your feature is unsafe. You can then check if the features perform correct evaluations, throws an exception, returns an error code, or do whatever it is supposed to do in these cases. If your project implement unit tests (I could argue that every project should, but it’s not always up to the developers), then you have a pretty direct way to check for overflows.įor the data and functions that can accept very high numbers, just throw big ints into them. ![]() If your test run is not exhaustive enough, you run the risk to let an overflow slip. The main downside of a dynamic checker like this one is that you’ll have to do a full compilation and an exhaustive test run of your program to detect overflows. I may be wrong, but I did not see any integration in other compilers. GCC Undefined Behavior Sanitizer – ubsan | Red Hat Developer.UndefinedBehaviorSanitizer - Clang 13 documentation ().It is implemented for both clang and GCC: ![]() It has the ability to detect integer overflows in the form of compilation options (though it is supposed to check UBs, it also do us the favor to check unsigned overflows): clang++ -fsanitize=signed-integer-overflow -fsanitize=unsigned-integer-overflow Undefined Behavior Sanitizer, UBSan for short, is a runtime undefined behaviour checker. If you happen to know other ways to do so, feel free to share it in comments, so it can benefit to everyone. I will present a few way to detect overflow in this section. They just either lack consistency or easiness. While they are few, there are ways to detected integer overflows. Even if signed overflow is undefined behavior while unsigned is not, 99.9% of the time you want neither of them. This article will talk about both signed and unsigned integer overflow, without distinction. There is no consistent and easy way to detect them, let alone to statically detect them, and the will make your program inconsistent.
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