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The Celestial Resilience class feature of the Celestial warlock patron from Xanathar's Guide to Everything lets you grant temporary hitpoints to other creatures. The calculation is described as "half your warlock level + your Charisma modifier."
Does the division by two apply to just the level (level / 2 + Cha mod), or the entire sum ((level + Cha mod) / 2)?
There are no rules that say how adding and multiplying work in general to help us out here. There are also several other questions struggling with similar problems (credit to @someone_evil for digging those out). These other cases are about multiplication and an added modifier, for example:
On the last Jeremy Crawford has clarified that designer intent is you add the ability modifier only once, but his tweets are not considered official rules any more.
There is a rule about always rounding down, both in Xanathar's (p. 4) and the PHB (p. 7). As this is the only explict rule that deviates from commonly applied mathematical custom, a reasonable assumption is that normal operator precedence applies, with division being resolved first. This would mean other creatures get half your level (rounded down) plus your Charisma modifier. But the rules do not tell us so.
Since it is not explicit, ask your DM.
I will suggest that you not take phrases out of context, but read the whole 10th level ability to arrive at the answer.
Celestial Resilience
Starting at 10th level, you gain temporary hit points whenever you finish a short or long rest. These temporary hit points equal your warlock level + your Charisma modifier. Additionally, choose up to five creatures you can see at the end of the rest. Those creatures each gain temporary hit points equal to half your warlock level + your Charisma modifier.
While it would have been nice for them to provide an example in the text of Xanathar's, which begins with the Temp HP bonus for the Warlock and then addresses the bonus for allies, there are two steps to it. You have to assess
Your first example is the correct answer: (level/2) + (Cha Mod).
Because the intent is clear from the previous sentence that explains the Temp HP for the Warlock under the same ability before it addresses the warlock's allies.
Starting at 10th level, you gain temporary hit points equal to your Warlock level plus your Charisma Modifier.
A warlock with a 18 Cha at level 10 would have 14 Temp HP, broken down into 10(level) + 4(Cha Mod).
That is clearly two different quantities added together. Having established that basis, the text follows with:
Additionally, choose up to five Creatures that you can see at the end of the rest. Those creatures each gain Temporary Hit Points equal to half your Warlock level + your Charisma modifier.
Two separate quantities, added together: half Warlock level added to Charisma Mod.
The Charisma modifier term is unchanged, only the half your Warlock Level is changed from the base benefit for the Warlock. Therefore, five companions of that same Warlock, Cha 18 at level 10, would each get 9 Temp HP.
There is a feat that provides Temp HP that precedes this feature (it was in the PHB a few years before Xanathar's was published, and looks to have been the template they worked from). The feat gives your allies your level + Cha mod. The Celestial Warlock feature has the same pattern but is not quite as strong, and the feat recharges on a short or long rest.
You can spend 10 minutes inspiring your companions, shoring up their resolve to fight. When you do so, choose up to six friendly creatures (which can include yourself) within 30 feet of you who can see or hear you and who can understand you. Each creature can gain temporary hit points equal to your level + your Charisma modifier. A creature can't gain temporary hit points from this feat again until it has finished a short or long rest.
(FWIW, all three DM's I've had Celestial Warlocks under agree with this reading of the text).
