demo/connections/third-party/qr/qr.js
function isMasked(x, y) {
    var bit;

    if (x > y) {
      bit = x;
      x   = y;
      y   = bit;
    }

    bit   = y;
    bit  += y * y;
    bit >>= 1;
    bit  += x;

    return frameMask[bit] === 1;
  }
function isMasked(x, y) {
    var bit;

    if (x > y) {
      bit = x;
      x   = y;
      y   = bit;
    }

    bit   = y;
    bit  += y * y;
    bit >>= 1;
    bit  += x;

    return frameMask[bit] === 1;
  }
function isMasked ( x , y ) { var bit ; if ( x > y ) { bit = x ; x = y ; y = bit ; } bit = y ; bit += y * y ; bit >>= 1 ; bit += x ; return frameMask [ bit ] === 1 ; }
Check mask since symmetricals use half.
Check mask since symmetricals use half .