I'm actually building a tool that should convert a portamento value from linear frequency slide to amiga period table.

Basically, what I need is to know the math operations that XM does to apply always the same amount of notes; in this way maybe I could reverse the logic to get the relative mod portamento value.

To better understand what I mean, suppose an Xm with ticks=5.

Having a note of C1 and a portamento effect of 104, the note played would changed in C#1.

This doesn't happens on Mod however, because following the period table C1 note corresponds to 856 period

(see

https://greg-kennedy.com/tracker/modformat.html)

So in order to reach C#1 note, the relative portamento vale is 1x0B. (I.e. (856-808) / 4).

So the main question of the thread is, how I could port a portamento value based on linear slide to mod the mod logarithmic scale and translate this stuff to a math formula?

Thank you in advance and let me know if I was unclear please