How does it affect negative population? (population loss) would it speed it(meaning the code is simply POPGROWTH*BONUS), slow it or not affect it?

if($popg>0)
$popg*=$pop_growth_bonus;
else
$popg/=$pop_growth_bonus;

i dont get it :P, something about $pop...

Not sure if you're serious or not, but just in case: if your population is growing then the bonus is multiplied, increasing the pop you gain each turn. If you're losing population, then the value is divided by the bonus so that you lose less pop each turn.