I need to transform some lat,lon data to x,y data using Mercators projection.

This requires an algorithm that uses natural logarithms
(http://en.wikipedia.org/wiki/Mercator_projection  has the complete
formula).

Both EXSLT and FXSL have implementations of the log function, however
both solutions seem to ultimately rely on extensions.

I need to support the Firefox / Transformiix XSL processor which, as
far as I know, doesn't support  any extensions at all.

Does anyone have a pure XSL version of the log function or any other
ideas about how to do this?

Etienne