What does this line of code do ?

Question

Hi

Confused as to what this code does

for (L=0; L < levels; L++, N_half>>=1){
    func( y, N_half);
} // end: levels for loop

In particular this " N_half>>=1 "

Thanks

Answer 1

It advances the loop by dividing N_half by two at every iteration. It is equivalent to:

for (L=0; L<levels; ++L, N_half=N_half / 2) {
    ...
}

Answer 2

N_half>>=1 performs a 1-place bitwise shift-right on N_half, which (for non-negative numbers) divides it by 2.

>>= is to >> as += is to +.

Answer 3

If N_half is a positive or unsigned integer, it halves it.

Answer 4

It right shifts N_half by 1 (i.e. divides it by two) and stores the result back in N_half

Answer 5

This seems to be the same as

for (L=0; L < levels; L++)
{
  func(y, N_Half); 
  N_Half /= 2;
}

The question has been rephrased since I answered it, such that this is no longer valid, but added for completeness: If nothing else is done within the loop, it is equivalent to:

N_Half >>= levels;

Caveats:

• if N_Half < 2^levels (0 for several iterations)
• if N_Half < 0 (first rightshift will depending on the implementation make it a positive number)

Answer 6

>>= operator shifts number's digits k positions at right

examples:

binary form

N = 101010111 // 2-base  arithmetic system
N >>= 1; // `division` by 2
N: 010101011

decimal form

N = 123456 // 10-base  arithmetic system
N >>= 2; // `division` by 10^2
N: 001234

as usual, the numbers in memory are in binary form and >>=1 is equivalent to division by 2.