Write a function that returns the sum of its two parameters. The parameters and return values are both 64-bit integers. 64-bit operands are passed in two consecutive registers. Thus, the first parameter is in r0 and r1, while the second parameter is in r2 and r3, with the return value returned in r0 and r1.
long long add64 (long long a, long long b);
Expected solution length: Around 3 lines.
Write your solution here