PHP: How to get previous Sunday of a specific date in the past..?

[ttyX]

I'm retrieving an entry from a database with a date associated with it. I want to be able to get the previous Sunday and the next Saturday relative to that specific date to populate a jQuery datepicker.I know how to do it with the actual time/date with :\[code\]strtotime('last Sunday')\[/code\]but I don't know how to do that for a date other than now...Thanks.