Question

OK, what I’m trying to do may sound a bit complicated, but I still cannot figure it out :

• Let’s say we have an unsigned long long 64-bit integer
• I want to set some “Variable”-bit positions and get all possible derived numbers

E.g.

Pattern = 00000000XXXXX000XX000X 
Positions = 0,4,5,9,10,11,12,13

Result (Pattern, Positions) = {
    0000000000000000000000
    0000000000000000000001
    0000000000000000010000
    0000000000000000010001
    0000000000000000100000
    0000000000000000100001
    0000000000000000110000
    0000000000000000110001
    etc...
}

How should I go about that? Any ideas?

Answer 1

They’re too easy.

Make a mask of the bit positions you want to stay constant. On each iteration:

x |= mask;
++x;
x &= ~mask;