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C实现与 uint64_t 相同功能的类

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实现与 uint64_t 相同的类,如果平台不支持 uint64_t 的话,可以代替之。 目前只完成部分功能,其他功能敬请期待.

uint64.hpp 。

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#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

  。

uint64.cpp 。

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#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

test.cpp 。

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#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;
}

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