ext_atomic.h missing from SDK 5.1.7

I'm compiling a flext project that uses buffer and realized that ext_atomic.h (which is included from buffer.h in MaxAudioAPI) is nowhere to be found in the SDK. Do anyone know why ext_atomic.h is missing or have a copy?

Also, I was also able to compile this project by modifying buffer.h (removing #include "ext_atomic.h" and changing t_int32_atom to int) but I am getting weird EXC_BAD_ACCESS that may be related to buffer. I'm trying to figure out if modification to buffer.h has anything to do with this.

I have never used flext before and I may be encountering a flext problem (e.g. incompatibility with Max5, etc.). The project I'm trying to compile is adaptfilt by Edgar Berdahl: https://ccrma.stanford.edu/~eberdahl/Projects/AdaptFilt/index.html.

My dev environment is OS X 10.7.1, flext 0.5.2, MaxSDK 5.1.7 using Max 5.1.9.

Thank you in advance!
Toshiro