Maybe the compiler is telling you all the time what is wrong, see this warning: kernel.h:181:19: warning: operation on ‘sst’ may be undefined [-Wsequence-p

Maybe the compiler is telling you all the time what is wrong, see this warning: kernel.h:181:19: warning: operation on ‘sst’ may be undefined [-Wsequence-point] 181 | #define fpop(s) ((--s)->v.f) | ~^~~~ words.c:2185:27: note: in expansion of macro ‘fpop’ 2185 | if ( fpop(sst) <= fpop(sst) ) | ^~~~ For this piece of code: /**(binary) ge * "1 1 ge" * TRUE if TOS-1 is greater than or equal to TOS. */ begin(ge) if ( fpop(sst) <= fpop(sst) ) fpush(sst,TRUE); else fpush(sst,FALSE); end() That code does assume that the first fpop pops the top of the stack (TOS), and the second one pops the element below that (TOS-1), so "0 1 ge" should return false. But current gcc versions evaluate the calls in the opposite order, so it will return true: https://godbolt.org/z/v4TdvE83b https://godbolt.org/z/v4TdvE83b Also, you win your nerd sniping badge.