Integer function and NEWIND/icall

Hello, Could anyone please tell me how could i use an integer function in nonmem. I am trying to do some pop pkpd simulations In excel when I have Tabsolute > tmax, I can convert it to time lower than tmin by using integer function (if tabs>tmax INT(tabs-tmax)/24+1) I then use these integer values to get the time points after 24 48 or so on in terms of 24 hours. t'=tabs-(integer*24) I tried to do it by having multiple statements wherein ABST=TIME IF(TIME.GT.TMAX) ABST=TIME-24 IF(TIME.GT.TMAX+24) ABST=TIME-48 IF(TIME.GT.TMAX+48) ABST=TIME-72 IF(TIME.GT.TMAX+72) ABST=TIME-96 is this the only way or could i do it in some other way too. Also could someone please explain me as to what exactly are the "newind" and "ICALL"function. How would they help me in my simulations?? if there might be any example it would be great Thanks a lot