Bit manipulation, permutate bits
- by triktae
Hi.
I am trying to make a loop that loops through all different integers where exactly 10 of the last 40 bits are set high, the rest set low. The reason is that I have a map with 40 different values, and I want to sum all different ways ten of these values can be multiplied. (This is just out of curiosity, so it's really the "bitmanip"-loop that is of interest, not the sum as such.)
If I were to do this with e.g. 2 out of 4 bits, it would be easy to set all manually,
0011 = 7,
0101 = 5,
1001 = 9,
0110 = 6,
1010 = 10,
1100 = 12,
but with 10 out of 40 I can't seem to find a method to generate these effectively. I tried, starting with 1023 ( = 1111111111 in binary), finding a good way to manipulate this, but with no success. I've been trying to do this in C++, but it's really the general method(if any) that is of interest. I did some googling, but with little success, if anyone has a good link, that would of course be appreciated too. :)
