http://www.stringfunction.com/hex-decimal.html
http://www.calculatorpro.com/calculator/modulo-calculator/

Block #257748 hash in decimal: 227538544328062966004888208644466284604660868282826408848828

227538544328062966004888208644466284604660868282826408848828 mod 12222 = 196

Line 196 is: BN_clear_free(this);

Can you comment a bit on this line of code, please?

BN_clear_free(this); // sets the memory for the bignumber to all zeroes and frees the memory, thereby saving many trees and dolphins in the process.