Olding, 24, and his Ulster team mate Jackson, 26, both deny charges of raping the same woman during a party after returning from an Ireland tour of South Africa in June 2016. Jackson denies a further charge of sexual assault.
Olding took the stand to give evidence in the fifth week of the rape trial at Belfast Crown Court. Jackson gave his account of events on Wednesday.
Olding said he and Jackson had been drinking all day and he was "pretty drunk" when he left a nightclub around midnight to go to Jackson's home with four girls they met at the club.
But he said he was "in complete control of my actions".
Olding said he had decided to go to bed and went up to Jackson's room to sleep and when he got to the room he found Jackson lying on his back with the woman on top of him.
He turned to go but, he said, the woman "held out her hand as an invitation to stay". Olding said she performed a sex act on him, stopping to ask for a condom and to take off her top at his request.
Olding said he was "100 percent sure" what had happened had been consensual.
"If I thought it was not (consensual) nothing would have started and nothing would have continued," Olding said under cross-examination.
Also facing charges relating to the case are Blane McIlroy, who denies exposing himself, and Rory Harrison, who denies perverting the course of justice and withholding information.
Neither Olding nor Jackson, who have represented their country a combined 29 times, will play at club or national level until the matter is concluded, the Irish Rugby Football Union has said.
(Reporting by Ian Graham; Editing by Conor Humphries and Andrew Heavens)
