(50g) Normal Distribution

[Albert Chan]

For x = 16.4285 714286 (~ 115/7), Z(x) errors is much worse.

x²/2 suffered from double roundings, 134.948 979592 30612 ... => 134.948 979593

2 Exp method got Z(x) correctly = 9.84720 298683 e-60
Direct method shorted 687 ULP -> 9.84720 297996 e-60

Edit: above assumed calculator do half-round-up.
With halfway-to-even, direct method got 9.84720 298986 e-60, error = +303 ULP