tan 45 gives me 0.9999

Question

Why does tan 45(0.7853981633974483 in radian) give me 0.9999? What\'s wrong with the following code?

System.out.println(Math.tan(M         


        

Answer 1

The closest double to pi/4 is exactly 0x1.921fb54442d18p-1. The tangent of this double, to more bits than you need, is 0x1.fffffffffffff72cece67p-1. Rounding to the nearest double gives you exactly 0x1.fffffffffffffp-1 because 0x1.fffffffffffff72cece67p-1 is less than 0x1.fffffffffffff8p-1.