Is there a 128 bit integer in C++?

问题:

I need to store a 128 bits long UUID in a variable. Is there a 128-bit datatype in C++? I do not need arithmetic operations, I just want to easily store and read the value very fast.

A new feature from C++11 would be fine, too.

回答1:

GCC and Clang support __int128

回答2:

Checkout boost's implementation:

#include <boost/multiprecision/cpp_int.hpp>

using namespace boost::multiprecision;

int128_t v = 1;

This is better than strings and arrays, especially if you need to do arithmetic operations with it.

回答3:

Although GCC does provide __int128, it is supported only for targets (processors) which have an integer mode wide enough to hold 128 bits. On a given system, sizeof() intmax_t and uintmax_t determine the maximum value that the compiler and the platform support.

回答4:

Your question has two parts.

1.128-bin integer. As suggested by @PatrikBeck boost::multiprecision is good way for really big integers.

2.Variable to store UUID / GUID / CLSID or whatever you call it. In this case boost::multiprecision is not a good idea. You need GUID structure which is designed for that purpose. As cross-platform tag added, you can simply copy that structure to your code and make it like:

struct GUID
{
    uint32_t Data1;
    uint16_t Data2;
    uint16_t Data3;
    uint8_t Data4[8];
};

This format is defined by Microsoft because of some inner reasons, you can even simplify it to:

struct GUID
{
    uint8_t Data[16];
};

You will get better performance having simple structure rather than object that can handle bunch of different stuff. Anyway you don't need to do math with GUIDS, so you don't need any fancy object.

回答5:

use the TBigInteger template and set any bit range in the template array like this TBigInt<128,true> for being a signed 128 bit integer or TBigInt<128,false> for being an unsigned 128 bit integer. Hope that helps maybe a late reply and someone else found this method already.