PHP and date manipulation

I was wondering if anyone has developed some functions or classes for dealing with various date manipulations. I wrote a bunch of these for our Y2K project and I could port them to PHP or even to C and build a module for PHP but I would prefer not to reinvent the wheel if someone has it already. For example, I would need the following: Given a date, return date for the 1st of the month Given a date, return date for last day of the month Given a date, return 1st day of next month Given a date, return last day of previous month Given a date, a start date and an end date, return -1 if date is earlier than both, +1 if later than both, 0 if between or equal. Adjust day by a given number of days, months or years, positive or negative. Given a date, return number of days remaining in the month. Some of these are relatively trivial, others are more complicated, but I would be interested in any canned scripts you may have to solve these problems. Thanks Jeff