Accurate Normal Distribution for the HP67/97

[Albert Chan]

Hi, Dieter

I did not know about the ±499 exponent range. That is huge !

FIX-4 was based on ±99 exponent range, we have Z(x) = 0.0 if |x| ≥ 21.4
So, FIX-4 work: -5 RND for 1 ≤ |x| < 10, -6 RND for |x| ≥ 10

With ±499 exponent range, FIX-4 is too much.

Luckily, with revised 1 Exp method, adding correction terms is easy.

• instead of FIX-4, do -5 RND, this fixed |y| < 48*5e-4 = 0.024
• add 2 correction terms: y⁴/24, y⁵/120. Dropped y⁶/720 < 2.7e-13
  

OTTH, with FIVE correction terms, you might as well just call exp(y)