JPL Horizons Delta-T Algorithms - need to be revised

The current implementation of Stellarium regarding the JPL Horizons algorithms computing Delta-T is limited between 3000BC and 1620. Outside this range the current algorithm simply returns deltaT = 0.0, an unacceptable situation. Since JPL Horizons should be considered a reference, it seems important to me that Stellarium JPL Horizons algorithm be revised and be capable to at least reproduce the JPL Horizons application results with some accuracy.

I recently contacted by email Jon Giorgini:

Jon Giorgini Senior Analyst Solar System Dynamics Group (392R) Navigation and Mission Design Section Jet Propulsion Laboratory Pasadena, CA USA

He provided me with some clear guidance (though not the actual code used by JPL - as this is not authorized) on how to proceed in order to implement an algorithm in Stellarium that will reproduce results from the JPL Horizons app. Thanks to his input, I was able to complete a first draft of this implementation in a local (i.e my machine) version of Stellarium.

I was able to obtain the following performance (i.e. differences between JPL Horizons app and my version of Stellarium):

from 9999BC to 1962-01-20 : +/- 0.1 seconds differences from 1962-01-20 to 2650-01-25 : +/- 10 microseconds differences from 2650-01-25 to 9999AD : +/- 2 milliseconds differences

Note: JPL Horizons app clamps deltaT from Present to 9999AD to the latest EOP (Earth Orientation Parameter) prediction. So values of deltaT from Present up to 9999AD are not really meaningful.

If this is of some interest for the upcoming release of Stellarium in December 2025, please indicate how I should proceed. I have done one simple Pull Request in the past, so I assume this would be the way to go...unless you would like to verify few aspects of the implementation with me before engaging in this formal process.