In the pull request #72 commit 1fd8f78 CONVERT_SAT was removed from the syntax of cvtop

- syntax cvtop = | CONVERT | REINTERPRET | CONVERT_SAT
+ syntax cvtop = | CONVERT | REINTERPRET

However, it seems that with this change, we cannot express trunc_sat as it collides with trunc
So, I believe we need a replacement or a workaround for this problem