Compute RaptorQ encoding (repair) symbols from intermediate symbols C.
Per RFC 6330 §5.3.5.3, an encoding symbol for ISI X is the XOR of the intermediate symbols at column indices produced by Tuple[K', X]:
Enc[K', X] = C[b] + C[b+a] + ... + C[w+pb1] + C[w+pb1+a1] + ...where the LT chain walks the first d indices by step a modulo w,
and the PI chain walks d1 indices by step a1 modulo p1 with
boundary-crossing via move_down.
Summary
Functions
Compute one encoding symbol for the given intermediate symbols, SIOP parameters, and ISI.