The currently used PEAC16x2 scrambler is nice but has two weaknesses :

1. sub-par mixing
2. the "mark" bits are too dependent on the input data

This was already considered back in 170. TODO: scan and elaborated with 1. Let's start.

The solution : a gPEAC chosen for its MSB and LSB.

Ideally, a "perfect" modulus should be chosen but the LSB are always 10. It was considered as a problem, since I wanted to reduce the size of the extra constant adder, so a string of 0s would have been great (or 1s...)

The new strategy is to reuse the existing adder and include the constant as a simplified MUX at the operands. The corresponding register gets updated only if a carry is generated.