H->HMS conversion HP-15C vs. HP42S vs HP67

[Albert Chan]

Above error bound can be tighten a bit, since we know scaling factor ~ 100.0

m1 and m2 are related by the factor k = m3/2^53 = 0.78125

If m1/2^53 >= 0.64, m2/m1 = k, otherwise m2/m1 = 2*k

With factor 100.0:

Max absolute error = 0.5 + 0.5 m2/m1 = 0.5 + k ~ 1.28 ULP
+1 ULP fix reduce this to k - 0.5 ~ 0.28 ULP

With factor 100.00000000000001:

Max absolute error = 0.5 + 0.5 m2/m1 - min(m2/m3)

If m1/2^53 >= 0.64, error = 0.5 + 0.5 k - 0.5/k ~ 0.25 ULP
Otherwise, error = 0.5 + 0.5 (2 k) - k/k = k - 0.5 ~ 0.28 ULP

Both approach have the same lower bound !