#define LOWBIT (x) (x) & (-X) principle detailed

#define LOWBIT (x) ((x) & (-X))

Can also be written as follows:

int Lowbit (x) {

Return x& (-X);

}

For example:

1> x = 1:

Decimal to binary (the number of bits is 8):

1 = 0000 0001

-1=> 1111 1111(here is the complement of 1)

The bits operation for 1& (-1) is (same as 1 XOR 0):

So 1& (-1) =1

2> x = 6:

Decimal to binary (the number of bits is 8):

6 = 0000 0110

-6=> 1111 1010(here is the complement of 6)

The bits operation for 6& (-6) is (same as 1 XOR 0):

So 6& (-6) =2

Summarize:

Find the 2^p (where the binary representation of p:x, the right-to-left number is the first 1 position),

If the binary representation of 6 is 110, the left number 0th is 0, the first is 1, then p=1,

So Lowbit (6) = 2^1 = 2.

Or directly understood as: Binary bitwise AND operation, returns the maximum quadratic factor of 2 less than X

Start in: 2016-03-18, 16:37:32

#define LOWBIT (x) (x) & (-X) principle detailed