I have written "the crash is due to out of bound accesses" which can be fixed by those changes (with %79), in the sense that the crash does not happen anymore when those bounds are enforced and therefore it proves in my eyes that those specific calls are the culprit. period.
I hope this is an issue with language barrier, because if it isn't, you're digging a whole for yourself. Those are not "calls" - they are array accesses. They are not the "culprit" for any definition of the word. The fact that they crash is a symptom. The culprit causing out-of-bound accesses is probably miles away. This is what I jokingly call "forensic debugging" at work. You can easily see that things aren't as they should be, but the trick is working backwards to discover what got them into that state. It isn't easy.
Also, %79 doesn't do what you want, anyway: that produces a number in the range 0..78 so attempting to access the last element in the array would wrap around to the first. You want %80 if anything, but as everyone has already mentioned, it's an expensive non-fix for an issue elsewhere. Treating the symptom doesn't cure the disease.