C实现与 uint64_t 相同功能的类

#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_ENDIAN
struct maybe_big_endian : std::true_type {};
#elif __BYTE_ORDER == __LITTLE_ENDIAN
struct 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(); // 先计算 second，预防 (this == &o) 的情况
 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("主机字节序是 big-endian\n");
 } else {
  std::printf("主机字节序是 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;
}