85. For sign-and-trade transactions (see question number 92), the outgoing salary for players who are subject to what was previously referred to as Base Year Compensation is either the previous salary or 50% of the new salary, whichever is greater (see question number 93).
92. For example, a player made $5 million last season, is a Larry Bird free agent, and re-signs with his previous team for $10 million. The team is a taxpayer, and therefore is over the cap following the signing. The signing is part of a sign-and-trade transaction for another team's $10 million player. Since the BYC conditions were satisfied the player's outgoing salary for the trade portion of this sign-and-trade transaction is $5 million. This trade therefore would not be allowed, even though the players' new salaries match, since a taxpaying team cannot trade a $5 million player for a $10 million player. The highest salary this team could acquire in a sign-and-trade arrangement is $6.35 million2.
Once a sign-and-trade is complete, the player's actual salary is included in his new team's team salary.
This is on CBA FAQ by Larry Coon.