Question

I cannot figure out what the difference between the following pieces of code is:

int t = __double2int_rd(pos.x/params.cellSize.x*2.0)&1;
if( t ==0) {...}

and

if(__double2int_rd(pos.x/params.cellSize.x*2.0)&1 == 0) {...}

The second option never returns true, while the first behaves as expected.

Does anyone have any ideas?

Answer 1

The second expression first evaluates (1==0) whose result is always false. Then ANDs it with the result of the function __double2int_rd.

Therefore it actually evaluates:

if(__double2int_rd(pos.x/params.cellSize.x*2.0) & 0)

Which would always be false.

The equivalent of the first expression would be:

if((__double2int_rd(pos.x/params.cellSize.x*2.0) & 1) == 0)

Mind the brackets.
Its a good programming practice to add brackets if you are not sure about the order of evaluation of expressions.