'Swore' in the Bible

May God punish Abner and do so severely if I don’t do for David what the Lord swore to him:

And all the people came to cause David to eat bread while it was yet day; but David swore, saying, So do God to me, and more also, if I taste bread or aught else till the sun be down!

And the king said to Shimei, Thou shalt not die. And the king swore to him.

But Abishai son of Zeruiah came to his aid, struck the Philistine, and killed him. Then David’s men swore to him: “You must never again go out with us to battle. You must not extinguish the lamp of Israel.”