#include <endian.h>#include <cstdint>#include <type_traits>#include <array> #define MC_BEGIN_NAMESPACE namespace mc {#define MC_END_NAMESPACE } MC_BEGIN_NAMESPACE #if __BYTE_ORDER == __BIG_ENDIANstruct maybe_big_endian : std::true_type {};#elif __BYTE_ORDER == __LITTLE_ENDIANstruct maybe_big_endian : std::false_type {};#else#error "Endianness not defined!"#endif template<typename Array, bool>struct uint64_data : public Array{protected: uint32_t& first() { return (*this)[0]; } uint32_t& second() { return (*this)[1]; } uint32_t first() const { return (*this)[0]; } uint32_t second() const { return (*this)[1]; }}; template<typename Array>struct uint64_data<Array, true> : public Array{protected: uint32_t& first() { return (*this)[1]; } uint32_t& second() { return (*this)[0]; } uint32_t first() const { return (*this)[1]; } uint32_t second() const { return (*this)[0]; }}; class uint64 : public uint64_data<std::array<uint32_t, 2>, maybe_big_endian::value>{public: uint64() = default; //explicit uint64(uint32_t v); uint64(const uint64& o); ~uint64() = default; uint64& operator+=(const uint64& v) noexcept; uint64& operator<<=(unsigned int n) noexcept; uint64& operator>>=(unsigned int n) noexcept; operator uint32_t() { return first(); } friend void swap(uint64& l, uint64& r);}; inline uint64 operator+(const uint64& l, const uint64& r){ auto tmp = l; return tmp += r; } inline uint64 operator>>(const uint64& l, unsigned int n){ auto tmp = l; return tmp >>= n; } inline uint64 operator<<(const uint64& l, unsigned int n){ auto tmp = l; return tmp <<= n; } MC_END_NAMESPACE

#include "uint64.hpp" MC_BEGIN_NAMESPACE uint64::uint64(uint32_t v){ first() = v; second() = 0u;} uint64::uint64(const uint64& o){ *this = o;}  uint64& uint64::operator+=(const uint64& o) noexcept{ second() += o.second(); // 先計算 second，預防 (this == &o) 的情況 uint32_t old = first(); if ((first() += o.first()) < old) {  ++second(); } return *this;}  uint64& uint64::operator<<=(unsigned int n) noexcept{ if (n < 32) {  second() = (second() << n) | (first() >> (32 - n));  first() <<= n; } else if (n < 64) {  second() = first() << (n - 32);  first() = 0u; } else /*if (n >= 64)*/ {  second() = first() = 0u; } return *this;}  uint64& uint64::operator>>=(unsigned int n) noexcept{ if (n < 32) {  first() = (first() >> n) | (second() << (32 - n));  second() >>= n; } else if (n < 64) {  first() = second() >> (n - 32);  second() = 0u; } else /*if (n >= 64)*/ {  second() = first() = 0u; } return *this;} void swap(uint64& l, uint64& r){ if (&l != &r) {  auto tmp  = l.first();  l.first() = r.first();  r.first() = tmp;  tmp    = l.second();  l.second() = r.second();  r.second() = tmp; }} MC_END_NAMESPACE

#include <cstdint>#include <cstdio>#include "uint64.hpp" #if 1 typedef mc::uint64 U64; inline void ptype() {std::printf("使用 mc::uint64/n");}#else typedef std::uint64_t U64; inline void ptype() {std::printf("使用 std::uint64_t/n");}#endif void frm(const char* str) { std::printf("%20s", str);} void data_hex(const U64& v) { const uint8_t* p = (const uint8_t*)&v; for (int i = 0; i < 8; ++i) {  if (i == 4) std::printf(" ");  std::printf("%02x", p[i]); } std::printf("/n");} void test() { uint32_t v = 0xffffffff; U64 a = v; frm("(a = 0xffffffff) => "); data_hex(a);   frm("(a >>= 1) => "); data_hex(a >>= 1);   a = v; frm("(a <<= 1) => "); data_hex(a <<= 1);   a = v; frm("(a += a) => "); data_hex(a += a);} int main() { ptype(); if (mc::maybe_big_endian::value) {  std::printf("主機字節序是 big-endian/n"); } else {  std::printf("主機字節序是 little-endian/n"); } for (int i = 0; i < 20; ++i)  std::printf(" "); if (mc::maybe_big_endian::value)  std::printf("H <<<< L H <<<< L/n"); else  std::printf("L >>>> H L >>>> H/n"); test(); return 0;}