ATK between Double and Half

if a monsters atk (lets say 1000) was halved by for example blackwing gale the whirlwind to (500)
then that monster was equipped with megamorprh which doubles or halves the original atk

what would be the effect of megamorph on its atk points?

wikia wrote:

While your Life Points are lower than your opponent's, the original ATK of the equipped monster is doubled. While your Life Points are higher, the original ATK of the equipped monster is halved.

1000 ATK is its original attack. When you halave it it becomes 500 points. When you use Megamorph, it gain same amount of its original ATK. This mean it becomes 1500 points.

If you halve ATK of a monster that gained an amount of ATK points (let's say 1000+800) there is two conditions:
1. If halving effect says "halve the original ATK" it becomes 1300 (1000/2+800).
2. If halving effect says "halve the ATK" it becomes 900 (1800/2).

I hope this helped.

Ok,, ill try to make this a little simpler, and get to the point. 1000 ATK halved to 500 ATK.... 1000 is the "original ATK" ,,, 500 is the "modified ATK" ,, the difference is 500 so there will be "-500" to get the total... When your LP is lower than your opponent you gain x2 "original ATK" so atk get to "2000" and then "-500" to achieve the "modified ATK" 1500 ATK. Hope that helps. ^^