[Prev] Table Of Contents

Using the Simple DirectMedia Layer API

Endian independence

  • Determine the endianness of the current system

The C preprocessor define SDL_BYTEORDER is defined to be either SDL_LIL_ENDIAN or SDL_BIG_ENDIAN, depending on the byte order of the current system.

A little endian system that writes data to disk has it laid out:
     [lo-bytes] [hi-bytes]
A big endian system that writes data to disk has it laid out:
     [hi-bytes] [lo-bytes]

Tip:
x86 systems are little-endian, PPC systems are big-endian.
Example: 
#include "SDL_endian.h"

#if SDL_BYTEORDER == SDL_LIL_ENDIAN
#define SWAP16(X)    (X)
#define SWAP32(X)    (X)
#else
#define SWAP16(X)    SDL_Swap16(X)
#define SWAP32(X)    SDL_Swap32(X)
#endif
  • Swap data on systems of differing endianness

SDL provides a set of fast macros in SDL_endian.h, SDL_Swap16() and SDL_Swap32(), which swap data endianness for you. There are also macros defined which swap data of particular endianness to the local system's endianness.

Tip:
If you just need to know the system byte-order, but don't need all the swapping functions, include SDL_byteorder.h instead of SDL_endian.h
Example: 
#include "SDL_endian.h"

void ReadScanline16(FILE *file, Uint16 *scanline, int length)
{
    fread(scanline, length, sizeof(Uint16), file);
    if ( SDL_BYTEORDER == SDL_BIG_ENDIAN ) {
        int i;
        for ( i=length-1; i >= 0; --i )
            scanline[i] = SDL_SwapLE16(scanline[i]);
    }
}

[Prev] Table Of Contents