Program to count number of set bits in an (big) array

Source

Interesting part of the solution is to see how the look up table is formed

    0, 1, 2, 3  0 - 0, 1, 1, 2 -------- GROUP_A(0)

 4 - 1, 2, 2, 3 -------- GROUP_A(1)

16 - 1, 2, 2, 3 -------- GROUP_A(1)

20 - 2, 3, 3, 4 -------- GROUP_A(2)

 8 - 1, 2, 2, 3 -------- GROUP_A(1)

12 - 2, 3, 3, 4 -------- GROUP_A(2)

24 - 2, 3, 3, 4 -------- GROUP_A(2)

28 - 3, 4, 4, 5 -------- GROUP_A(3) ... so on