A recursive routine, if more than a few levels deep, could stress the 8051 or even 8052 stack beyond capacity. Jez talkes about numbers with 4096 bits if data in each number. That is ((2^{^^}4096)-1) or about 1235 significant digits of resolution. Recursion on this number of digits could be asking for 32K bytes or more of stack space !!

Michael Karas