jbapple / 128-bit-literals

Library for literal 128-bit integers in C++

128-bit literals in C++11 and C++14

In C++, you can store 8-bit integers, 16-bit integers, 32-bit integers, and 64-bit integers:

int8_t alice;
int64_t bob;

GCC and Clang even have 128-bit integers:

__int128 carol;

You can store 128-bit integers, but you aren't allowed to write 128-bit integers:

__int128 dave = 18446744073709551616;

error: integer literal is too large to be represented in any integer type
__int128 dave = 18446744073709551616;
                ^

This library allows you to write 128-bit integers:

#include "suffix128.hpp"
__int128 emily = 18446744073709551616_128;

All you have to do is #include "suffix128.hpp" and end your integer with the suffix _128.

---

You can use the suffix _u128 for unsigned integers:

unsigned __int128 frank = 123456789012345678901234567890_u128;

128-bit integers you write this way are constants and they can be used as template parameters or enumerator initializers.

enum Bar { BAZ = 0_128 };

You can use C++14's single-quote digit separator:

__int128 gloria = 1'2'3'456'7_128;

You can also write them in hexadecimal or octal notation:

__int128 hector = 0xfeed'bad'beef'2'dad_128;
__int128 imelda = 0644_128;

You can even write 128-bit binary literals:

unsigned __int128 jules = 0b00000001000001100001010000111000100100010110001101000111100100110010101001011100110110011101001111101010110101111011011101111111_u128;