Question

How to convert a 32-bit number between big-endian and little-endian values in C

Answer 1

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    // 32 bit 

    // unsigned long _byteswap_ulong(unsigned long value); // VS

    unsigned long n = 1991994; //0x001E653A;

    printf("%X\n", n);

    n = _byteswap_ulong(n);

    printf("%X\n", n);
}



/*

001E653A
3A651E00

*/

 

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Answer 2

#include <stdio.h>

unsigned long toLittleEndian(unsigned long value) {
    return ((value >> 24) & 0x000000FF) |
        ((value >> 8) & 0x0000FF00) |
        ((value << 8) & 0x00FF0000) |
        ((value << 24) & 0xFF000000);
}

int main(void)
{
    // 32 bit 

    unsigned long n = 1991994; //0x001E653A;

    printf("%X\n", n);

    n = toLittleEndian(n);

    printf("%X\n", n);
}




/*

001E653A
3A651E00

*/

 

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Answer 3

#include <stdio.h>
#include <stdint.h>

int main(void)
{
    // 32 bit 
  
    // uint32_t __builtin_bswap32 (uint32_t x) // GCC
  
    uint32_t n = 1991994; //0x001E653A;
  
    printf("%X\n", n);
  
    n = __builtin_bswap32(n);
  
    printf("%X\n", n);
}
  
  
  
/*

001E653A
3A651E00
  
*/
 

 

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