Let's see.

b = (z * a + !z * b) - (z * b + !z * a);

b = z*a + !z*b - z*b - !z*a;

b = z*a - z*b + !z*b - !z*a;

b = z*(a - b) + !z*(b - a);

b = z*(a - b) - !z*(a - b);

b = (z - !z)*(a - b);

Yep. It looks like they're equivalent. Regarding #2, I am assuming 0 = false, and 1 = true? Or is any r <> 0 considered true?