Disputatio:Index formarum Latinarum nominum Arabicorum Persicorumque
Hamadus/Hamidus/Hamedus
recensereThere is an issue with the name(s) having the Arabic triconsonantal root Ḥ-M-D (ح م د): You will find people named حامد (Ḥāmid/Ḥāmad), حمید (Ḥamīd) or حمد (Ḥamad). حامد apparently means "Lauder", while حمید means "Lauded" (no idea about the third one).
Likewise, in Latin, you will find Hamadus, Hamidus and Hamedus. I very much doubt that there was anything systematic in the choice of one of those versions.
Now, one possibility would be to assigne حمید to Hamidus (because of the long i) and the two others arbitrarily (say حامد to Hamedus and حمد to Hamadus). But then we would e.g. end up with a Hamedus (or Hamadus) Karzai whom everybody else calls Hamid.
Or we don't care (just as I suspect earlier Latinists haven't) and assign one of the Latin forms according to the most frequent rendering in the vernaculars, without bothering about the exact Arabic spelling.