I'm trying to find a way to handle several bitfield cases that include optional, required, and not allowed positions.
yy?nnn?y
11000001
?yyy?nnn
01110000
nn?yyy?n
00011100
?nnn?yyy
00000111
In these four cases, the ? indicates that the bit can be either 1 or 0 while y indicates a 1 is required and n indicates that a 0 is required. The bits to the left/right of the required bits can be anything and the remaining bits must be 0. Is there a masking method I can use to test if an input bit set satisfies one of these cases?
Absolutely, but of course it depends on how you represent the "templates".
For example, say you represent them as a pair (z, o) where z has a 1 for every bit that is allowed to be 0 and o has a 1 for every bit that is allowed to be 1 (as in the paper I linked to in the comments). Then to test x against it you could do:
if ((x | z) == -1 && (x & o) == x)
passes test
You could also represent the templates as a pair (mask, bits), where mask is a mask of all bits that have to match (ie 0 means ?, 1 means a fixed bit) and bits is the values of the fixed bits. Then you could test x like:
if ((x & mask) == bits)
passes test
That's in general. If your problem has a special form, as it does in your question, you could use specialized tests.