You could use POSIX, like husoft suggested, or use int:

$num = 5.2;
if ($num > 0) {
  $floor = int($num);
  $ceil = int($num) == $num ? $num : int($num)+1;
} else {
  $floor = int($num) == $num ? $num : int($num)-1;
  $ceil = int($num);
}
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Updated: updated to deal with negative numbers correctly, as rir pointed out.

-- Dan