Question

How to convert a 64-bit number between big-endian and little-endian values in C++

Answer 1

#include <iostream>

int main(void)
{
    // 64 bit 

    // unsigned __int64 _byteswap_uint64(unsigned __int64 value); // VS

    unsigned __int64  n = 0x8877665544332211;

    std::cout << std::hex << std::uppercase << n << "\n";

    n = _byteswap_uint64(n);

    std::cout << std::hex << n << "\n";
}



/*

8877665544332211
1122334455667788

*/

 

70+ SQL courses for beginners and professionals

Answer 2

#include <iostream>

uint64_t toLittleEndian(uint64_t value) {
    return ((value >> 56) & 0x00000000000000FFULL) |
           ((value >> 40) & 0x000000000000FF00ULL) |
           ((value >> 24) & 0x0000000000FF0000ULL) |
           ((value >> 8) & 0x00000000FF000000ULL) |
           ((value << 8) & 0x000000FF00000000ULL) |
           ((value << 24) & 0x0000FF0000000000ULL) |
           ((value << 40) & 0x00FF000000000000ULL) |
           ((value << 56) & 0xFF00000000000000ULL);
}

int main(void)
{
    // 64 bit 

    unsigned __int64  n = 0x8877665544332211;

    std::cout << std::hex << std::uppercase << n << "\n";

    n = _byteswap_uint64(n);

    std::cout << std::hex << n << "\n";
}



/*

8877665544332211
1122334455667788

*/

 

70+ SQL courses for beginners and professionals

Answer 3

#include <iostream>
#include <cstdint>

int main(void)
{
    // 64 bit 
 
    // uint64_t __builtin_bswap64(uint64_t x) // GCC
 
    uint64_t  n = 0x8877665544332211;
 
    std::cout << std::hex << std::uppercase << n << "\n";
 
    n = __builtin_bswap64(n);
 
    std::cout << std::hex << n << "\n";
}
 
 
 
/*
 
8877665544332211
1122334455667788
 
*/
 

 

70+ SQL courses for beginners and professionals