How to determine the number of unique recent committers on a branch?

Hi,

I'm trying to determine the number of unique committers who have recently committed to a branch. "Recently" should be configurable, but for my example I'll use a period of 3 months.

At first, I thought the [<refname>]@{<date>} syntax [1] in conjunction with git "shortlog -s" could be helpful here, like

$ git shortlog -s main@{3.months.ago} | wc -l

But then I realized that just like with the --since option, the <date> counts relative to the current date, not relative to the date of the last commit on the given branch. To me, that's rather counterintuitive for the [<refname>]@{<date>} syntax.

So, what would be a good way to achieve what I want with only Git-means (and maybe `wc`), but without any awk / Perl scripting magic?

Thanks in advance!

[1]: http://git-scm.com/docs/gitrevisions#Documentation/gitrevisions.txt-emltrefnamegtltdategtemegemmasteryesterdayememHEAD5minutesagoem