Using ranges in calculating a new map layer

[Lesley-Ann Dupigny]

Hello GRASS-Users

I am trying to extract out certain ranges of values from one of my map 
layers and apply a formula to it to produce a new one. From my 
understanding of r.infer and r.mapcalc, it would seem that I need a 
combination of both modules, so that I could essentially come up with the 
following

		IFMAP temperature x-y
		THEN r.mapcalc newtemp='(temperature*2)-50'

One way of accomplishing what I want to do would be to create a MASK that 
eliminates all temperatures that lie outside the x-y range. However, 
given that this range includes about 3000 categories, I was wondering if 
there was a more efficient way of tackling this problem.

Thanks and looking forward to any suggestions.

Lesley-Ann Dupigny.