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. :-)

#!/bin/sh
#
echo "Generating build information using autoconf"
echo "This may take a while ..."

# Regenerate configuration files
cp acinclude.m4 aclocal.m4
found=false
for autoconf in autoconf autoconf259 autoconf-2.59
do if which $autoconf >/dev/null 2>&1; then $autoconf && found=true; break; fi
done
if test x$found = xfalse; then
    echo "Couldn't find autoconf, aborting"
    exit 1
fi
(cd test; sh autogen.sh)

# Run configure for this platform
echo "Now you are ready to run ./configure"