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Fair enough. havent got a clue on my problem have you?

I am not familiar with PHP, but I believe you could use the decbin function to get a string representation of the given decimal number in binary. After this, you would simply need to check whether the Nth bit equals 1.

There are probably much better approaches, but this should do the job.

Edit: base_convert(string $number, int $frombase, int $tobase) may also be of interest.

What are you trying to accomplish? I'm not sure what $isbit does.

According to mIRC's help docs,

$isbit(A,N)
Returns 1 if the Nth bit in number A is turned on.

What kind of conversions are you looking at?