what do these commands do

Question

Could anyone explain what the commands

@tempcntb

count@@ne

@curtab

For reference, I found them on How to produce a list of prime numbers in LaTeX
i do understand that i can create new counts with
catcode`@=11 %makeatletter

newcount@tempcntb
newcount@curtab

catcode`@=12 %makeatother

but i don't see it appear in the macro, so i don't really understand them.

David Carlisle · Accepted Answer

You linked to the question but I assume you mean this code from my answer
makeatletter
defprimes#1#2{{%
  defcomma{defcomma{, }}%
  count@@ne@tempcntb#2relax@curtab#1relax
  @primes}}
def@primes{loopadvancecount@@ne
expandafterifxcsname p-thecount@endcsnamerelax
ifnum@tempcntb<count@else
  ifnumcount@<@curtabelsecommathecount@fifielserepeat
@tempcntacount@loopadvance@tempcntacount@
expandafterletcsname p-the@tempcntaendcsname@ne
ifnum@tempcnta<@tempcntbrepeat
ifnum@tempcntb>count@expandafter@primesfi}
makeatother

@tempcntb and @currtab are scratch count registers that are already defined by latex so you do not need newcount (the first one intented for temporary use like this, the second one less so, it is normally used by tabbing
count@@ne is primitive syntax which sets the counter to 1.

egreg · Answer

@tempcntb is a scratch counter allocated by the LaTeX kernel, so it's always available.
It's similar for count@, which uses count255 and is historically a scratch register.
@curtab is instead a counter used in the code for tabbing and should not be used otherwise. (Not a capital sin in the particular usage, but not good programming style nonetheless.)
The available scratch counters in LaTeX are
count@
@tempcnta
@tempcntb

what do these commands do

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