Thanks for the last note, specifically because I was aware of it, though I was lazy with an explanation, never a good thing, so thanks for bringing this to my attention
In response to your explanation, the FF's baffled me as to a hidden meaning, though I ran with it and re-read both Prelude's explanation and knr's.
~(~0 << (p+1-n))
I couldn't understand the impact of either side of the expression.
Now it reads:
complement bits (p+1-n) from right to left, and then complement the remainder.
EG:
11111111
11111100
00000011
Ahh I understand now, even if it doesn't look like it
Thank you both very much. Really big help.