At the moment, outout selection is random. There is no coin control code. If you're interested, the latest MRL bulletin discusses some of these issues: https://lab.getmonero.org/pubs/MRL-0004.pdf
Selection of inputs to spend
pvas posted this 9 years ago
Good day, I am new here Spent some time reading of Monero. Good guy FlailingBorg (http://www.reddit.com/r/Monero/comments/2f05jp/privacy_with_low_transaction_volume_wallets/) had a question of spending related outputs in a single transaction. It destroys the mixing efforts I think. I can not say how system selects outputs when user sends a transfer. Duz anyone now is it possible for user to manually select the outputs to spend when he sends XMR? Duz any client support this feature?