I've made so many changes I don't dare continue until I check the current stuff in. /test/testatomic.c performs absolutely basic tests to show that the function work as expected. Need a second test to do more detailed tests. /include/SDL_atomic.h provides declarations for all included functions. /src/atomic/linux/SDL_atomic.c provided all the functions. On a generic built the 64 bit functions work, but they are emulated. On a build for -march=pentium and above the 64 bit functions use native instructions /src/atomic/dummy/SDL_atomic.c emulates all the operations using SDL_mutex.h. /src/atomic/win32/SDL_atomic.c is a copy of dummy /src/atomic/macosx/SDL_atomic.s is a copy of dummy These versions of SDL_atomic.c provide a frame work for building the library with a mixture of native and emulated functions. This allows the whole library to be provided on all platforms. (I hope.) I hope this fits with the SDL philosophy of either providing a common subset or emulating when the platform is missing a feature. I have not added dummy, macosx, or win32 to the build. They are there as place holders for future work. I have modified congifure.in to compile sources in /src/atomic/linux. (The SDL configure.in file is an amazing piece of work and I hope I didn't mess it up. :-)

/* A simple test program framework */

#include <SDL/SDL.h>

#define VERBOSE_VIDEO   0x00000001
#define VERBOSE_MODES   0x00000002
#define VERBOSE_RENDER  0x00000004
#define VERBOSE_EVENT   0x00000008
#define VERBOSE_AUDIO   0x00000010

typedef struct
{
    /* SDL init flags */
    char **argv;
    Uint32 flags;
    Uint32 verbose;

    /* Video info */
    const char *videodriver;
    int display;
    const char *window_title;
    Uint32 window_flags;
    int window_x;
    int window_y;
    int window_w;
    int window_h;
    int depth;
    int refresh_rate;
    int num_windows;
    SDL_WindowID *windows;

    /* Renderer info */
    const char *renderdriver;
    Uint32 render_flags;
    SDL_bool skip_renderer;

    /* Audio info */
    const char *audiodriver;
    SDL_AudioSpec audiospec;
} CommonState;

extern CommonState *CommonCreateState(char **argv, Uint32 flags);
extern int CommonArg(CommonState * state, int index);
extern const char *CommonUsage(CommonState * state);
extern SDL_bool CommonInit(CommonState * state);
extern void CommonEvent(CommonState * state, SDL_Event * event, int *done);
extern void CommonQuit(CommonState * state);