[Bits manipulation]

align:

 return (value + align_size - 1) & (~(align_size - 1);

has_single_bit:

 return x && !(x & (x - 1));

midpoint:

  return (a & b) + (a ^ b) / 2;

負i保 減一去

Set union A | B 

Set intersection A & B 

Set subtraction A & ~B 

Set negation ALL_BITS ^ A or ~A 

Set bit A |= 1 << bit 

Clear bit A &= ~(1 << bit) 

Test bit (A & 1 << bit) != 0 

Extract last bit A & -A or A & ~(A - 1) or x ^ (x & (x - 1)) 

Remove last bit A & (A - 1) 

Get all 1-bits ~0