Count function

Is there anyway of counting up from 0 in a Perch template in a loop? I can do it from 1 or an ID number but Bootstrap's default carousel (and perhaps other JS-powered slideshows?) uses a "from zero counting method" to list its navigation buttons. It would be great if there was a customisable count tag for things like this? Something like <perch:count from="0" /> would be awesome :) !

ps Has anyone else solved this with javascript?

Many thanks in advance.

Jon