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. :-)

#define picture_width 32
#define picture_height 32
static char picture_bits[] = {
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18, 0x80, 0x01, 0x18,
   0x64, 0x6f, 0xf6, 0x26, 0x0a, 0x00, 0x00, 0x50, 0xf2, 0xff, 0xff, 0x4f,
   0x14, 0x04, 0x00, 0x28, 0x14, 0x0e, 0x00, 0x28, 0x10, 0x32, 0x00, 0x08,
   0x94, 0x03, 0x00, 0x08, 0xf4, 0x04, 0x00, 0x08, 0xb0, 0x08, 0x00, 0x08,
   0x34, 0x01, 0x00, 0x28, 0x34, 0x01, 0x00, 0x28, 0x12, 0x00, 0x40, 0x48,
   0x12, 0x20, 0xa6, 0x48, 0x14, 0x50, 0x11, 0x29, 0x14, 0x50, 0x48, 0x2a,
   0x10, 0x27, 0xac, 0x0e, 0xd4, 0x71, 0xe8, 0x0a, 0x74, 0x20, 0xa8, 0x0a,
   0x14, 0x20, 0x00, 0x08, 0x10, 0x50, 0x00, 0x08, 0x14, 0x00, 0x00, 0x28,
   0x14, 0x00, 0x00, 0x28, 0xf2, 0xff, 0xff, 0x4f, 0x0a, 0x00, 0x00, 0x50,
   0x64, 0x6f, 0xf6, 0x26, 0x18, 0x80, 0x01, 0x18, 0x00, 0x00, 0x00, 0x00,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};