Target player draws cards equal to half the number of cards in their library and loses half their life. Round up each time.
The life lost is rounded up, not the remaining life total. For example, if the target player has 7 life, they lose 4 life and end up with 3. Similarly, the number of cards drawn is rounded up, not the number of cards remaining in the library.
To draw the cards, first the player determines how many cards to draw, then draws them. This event may be modified so that a different number of cards are actually drawn.