问题
This question already has an answer here:
- Is there a 128 bit integer in gcc? 3 answers
Does gcc support 128-bit int on amd64?
How to define it?
How to use scanf/printf to read/write it?
回答1:
GCC supports built-in __int128 and unsigned __int128 types (on 64-bit platforms only), but it looks like formatting support for 128-bit integers is less common in libc.
Note: <stdint.h> defines __int128_t and __uint128_t on versions before gcc4.6. See also Is there a 128 bit integer in gcc? for a table of gcc/clang/ICC versions.
How to know if __uint128_t is defined for detecting __int128
回答2:
void f(__int128* res, __int128* op1, __int128* op2)
{
*res = *op1 + *op2;
}
Save to test.c and compile with:
$ gcc -c -O3 test.c
$ objdump -d -M intel test.o
You get:
mov rcx, rdx
mov rax, [rsi]
mov rdx, [rsi+0x8]
add rax, [rcx]
adc rdx, [rcx+0x8]
mov [rdi], rax
mov [rdi+0x8], rdx
As you can see the __int128 type is supported by keeping two 64-bits in sequence and then operating on them with the typical big int pattern of using two instructions, for example ADD and then ADC (add with carry)
来源：https://stackoverflow.com/questions/3329541/does-gcc-support-128-bit-int-on-amd64