In the initial implemenation of the right-shift-and-cast operations only dealt with shift offsets greater than eight, but I realized I can be more general.

Here's a truth table for all possible right shifts and the equvalant general shift I need, including casting.

N Original pattern Shifted pattern Result Optimization
- ----------------- ----------------- -------- ----
0 01234567.89ABCDEF -> 01234567.89ABCDEF -> 89ABCDEF X<<8 -.
1 01234567.89ABCDEF -> x0123456.789ABCDE -> 789ABCDE X<<7 |
2 01234567.89ABCDEF -> xx012345.6789ABCD -> 6789ABCD X<<6 |
3 01234567.89ABCDEF -> xxx01234.56789ABC -> 56789ABC X<<5 | X<<(8-N)
4 01234567.89ABCDEF -> xxxx0123.456789AB -> 456789AB X<<4 |
5 01234567.89ABCDEF -> xxxxx012.3456789A -> 3456789A X<<3 |
6 01234567.89ABCDEF -> xxxxxx01.23456789 -> 23456789 X<<2 |
7 01234567.89ABCDEF -> xxxxxxx0.12345678 -> 12345678 X<<1 -'
8 01234567.89ABCDEF -> xxxxxxxx.01234567 -> 01234567 nop
9 01234567.89ABCDEF -> xxxxxxxx.x0123456 -> x0123456 X>>1 -.
A 01234567.89ABCDEF -> xxxxxxxx.xx012345 -> xx012345 X>>2 |
B 01234567.89ABCDEF -> xxxxxxxx.xxx01234 -> xxx01234 X>>3 |
C 01234567.89ABCDEF -> xxxxxxxx.xxxx0123 -> xxxx0123 X>>4 | X>>(N-8)
D 01234567.89ABCDEF -> xxxxxxxx.xxxxx012 -> xxxxx012 X>>5 |
E 01234567.89ABCDEF -> xxxxxxxx.xxxxxx01 -> xxxxxx01 X>>6 |
F 01234567.89ABCDEF -> xxxxxxxx.xxxxxxx0 -> xxxxxxx0 X>>7 -'