在C中赋值128位整数
在C中赋值128位整数
提问于 2015-07-17 01:57:25
在gcc 4.9.1中，当我尝试给一个128位整数赋值时，我得到了一个warning: integer constant is too large for its type。
示例代码
int main(void) {
__uint128_t p = 47942806932686753431;
return 0;
}输出
我正在用gcc -std=c11 -o test test.c编译，我得到了：
test.c: In function ‘main’:
test.c:2:19: warning: integer constant is too large for its type
__uint128_t p = 47942806932686753431;
^是我做错了什么，还是这是gcc的一个bug？
回答 1
Stack Overflow用户
发布于 2019-12-27 00:42:28
我也遇到了同样的问题，我想出了一个使用用户自定义文字的解决方案。下面是如何实例化用户定义的文本_xxl：
int main(int argc, char** argv) {
auto a = 0xF0000000000000000000000000000000LLU;
auto b = 0xF0000000000000000000000000000000_xxl;
printf("sizeof(a): %zu\n", sizeof(a));
printf("sizeof(b): %zu\n", sizeof(b));
printf("a == 0? %s\n", a==0 ? "true":"false");
printf("b == 0? %s\n", b==0 ? "true":"false");
printf("b >> 124 = %x\n", b >> 124);
return 0;
}输出：
sizeof(a): 8
sizeof(b): 16
a == 0? true
b == 0? false
b >> 124 = f下面是用户定义的文字_xxl的实现
#pragma once
#include <stdint.h>
#ifdef __SIZEOF_INT128__
using uint_xxl_t = __uint128_t;
using sint_xxl_t = __int128_t;
namespace detail_xxl
{
constexpr uint8_t hexval(char c)
{ return c>='a' ? (10+c-'a') : c>='A' ? (10+c-'A') : c-'0'; }
template <int BASE, uint_xxl_t V>
constexpr uint_xxl_t lit_eval() { return V; }
template <int BASE, uint_xxl_t V, char C, char... Cs>
constexpr uint_xxl_t lit_eval() {
static_assert( BASE!=16 || sizeof...(Cs) <= 32-1, "Literal too large for BASE=16");
static_assert( BASE!=10 || sizeof...(Cs) <= 39-1, "Literal too large for BASE=10");
static_assert( BASE!=8 || sizeof...(Cs) <= 44-1, "Literal too large for BASE=8");
static_assert( BASE!=2 || sizeof...(Cs) <= 128-1, "Literal too large for BASE=2");
return lit_eval<BASE, BASE*V + hexval(C), Cs...>();
}
template<char... Cs > struct LitEval
{static constexpr uint_xxl_t eval() {return lit_eval<10,0,Cs...>();} };
template<char... Cs> struct LitEval<'0','x',Cs...>
{static constexpr uint_xxl_t eval() {return lit_eval<16,0,Cs...>();} };
template<char... Cs> struct LitEval<'0','b',Cs...>
{static constexpr uint_xxl_t eval() {return lit_eval<2,0,Cs...>();} };
template<char... Cs> struct LitEval<'0',Cs...>
{static constexpr uint_xxl_t eval() {return lit_eval<8,0,Cs...>();} };
template<char... Cs>
constexpr uint_xxl_t operator "" _xxl() {return LitEval<Cs...>::eval();}
}
template<char... Cs>
constexpr uint_xxl_t operator "" _xxl() {return ::detail_xxl::operator "" _xxl<Cs...>();}
#endif // __SIZEOF_INT128__它可以像普通的整数常量一样在常量表达式中使用：
static_assert( 0_xxl == 0, "_xxl error" );
static_assert( 0b0_xxl == 0, "_xxl error" );
static_assert( 00_xxl == 0, "_xxl error" );
static_assert( 0x0_xxl == 0, "_xxl error" );
static_assert( 1_xxl == 1, "_xxl error" );
static_assert( 0b1_xxl == 1, "_xxl error" );
static_assert( 01_xxl == 1, "_xxl error" );
static_assert( 0x1_xxl == 1, "_xxl error" );
static_assert( 2_xxl == 2, "_xxl error" );
static_assert( 0b10_xxl == 2, "_xxl error" );
static_assert( 02_xxl == 2, "_xxl error" );
static_assert( 0x2_xxl == 2, "_xxl error" );
static_assert( 9_xxl == 9, "_xxl error" );
static_assert( 0b1001_xxl == 9, "_xxl error" );
static_assert( 011_xxl == 9, "_xxl error" );
static_assert( 0x9_xxl == 9, "_xxl error" );
static_assert( 10_xxl == 10, "_xxl error" );
static_assert( 0xa_xxl == 10, "_xxl error" );
static_assert( 0xA_xxl == 10, "_xxl error" );
static_assert( 0xABCDEF_xxl == 0xABCDEF, "_xxl error" );
static_assert( 1122334455667788_xxl == 1122334455667788LLu, "_xxl error" );
static_assert(0x80000000000000000000000000000000_xxl >> 126 == 0b10, "_xxl error");
static_assert(0x80000000000000000000000000000000_xxl >> 127 == 0b01, "_xxl error");
static_assert( 0xF000000000000000B000000000000000_xxl > 0xB000000000000000, "_xxl error" );页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/31461318
复制相关文章
相似问题