> Um, gack. You could do it with replication instead of shifts with
>>> something like:
>>>
>>> rights = ((old_mode & 0777 & who_masks[what_letter]) * 0111111) >> 9
>>> value = rights & 0777 & who_masks[who_letter]
>>>
>>>
>>
> (oops, hit send by mistake)
> Gack! That seems overly clever.
>
:) Yeah, but so did yours (I don't really like either of them). Mine was
basically the old unix trick of using multiplication to spread the what over
the who.
> Maybe something like:
> rights = (old_mode & 0777) / digits[what_letter]
> value = rights * digits[who_letter]
> (where digits maps [ugo] to 0100, 010, 01)
>
That's pretty much still the shift trick (which I think I like better than
the digits version).
I think the core problem is that all of the concerns have gotten merged (old
value propagation from [oug] on the right and don't care bits as
"unchanged"). Suppose we had a function and distribution over the who:
def basic_rights_mask(letters,old_mask = 0)
value = { 'r' => 4, 'w' => 2, 'x' => 1, 'u' => (old_mask >> 6) & 7,
'g' => (old_mask >> 3) & 7, 'o' => old_mask & 7 }
letters.split(//).
map { |ch| value[ch] || 0 }.
inject(0) { |mask,bits| mask | bits }
end
...and then an analog for s & t (I'm pretending X doesn't exist), we could
compute the "what" independent of the "who" (instead of having the nested
loops) and combine them with something like:
basic_who = { 'u' => 0100, 'g' => 0010, 'o' => 0001, 'a' => 0111 }
value = (basic_who[x] * basic_rights_mask(what,old_rights)) |
(extra_who[x] * extra_rights_mask(what,old_mask))
I don't know. Those are my thoughts, for what they are worth.
-- M
-----------------------------------------------------------
The power of accurate observation is
commonly called cynicism by those
who have not got it. ~George Bernard Shaw
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