HP-71B internal summation weakness in Math ROM

[J-F Garnier]

(06-04-2020 09:17 AM)Werner Wrote:  Hello JF.
What does your new version return for DOT([1E15 5 -1E15],[1 1 1]) ?
Werner

Good question !
It returns 10, as do the 28S and 42S (and series 48/49/50 I believe).

This is a good test, because it reveals another aspect related to half-way rounding.
With real numbers, 12-digit half way rounding (that is numbers ending exactly in between two possible rounded forms) is done with the round to even rule.
For the 15-digit rounded addition (as introduced in the 28C), half way rounding is always done upwards, probably for consistency.

To be clear, I don't argue on which system is better, I just wanted to make the HP-71B Math ROM consistent with the math routines used since the 28C up to the 50G.

J-F