int8 type substitute ?

Hello,
  I'm looking for a int8-like type or equivalent substitute.
  float8 is the first one that comes to mind, but a question arises : isn't there a chance that if I store float8
valuesbe integers, it may
 
on some occasions return to me a decimal ? I.e. I would store something
like2814749767106569
and on retrieval it would return something like2814749767106568.999999999998 instead of 2814749767106569 ?
  If there is such danger, what other suitable 8 byte data type (other
than char(8)) would there be in PG to give me the ablility to store
integers > 2^32 ?
 Or is it quite fast, easy, simple and performance-effective to add my
own 'int8' data type ?
   Thanx,
     Jan

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