[Algorithms] negative UV coords

[skunkwerk <sku...@gm...>]

hi,
   i'm looking for an explanation of what negative UV coordinates do when
using texture mapping.  my initial thought was that negative coordinates are
just a continuation in the same U-V plane of the tiled texture, so a value
of -1.6 would be equivalent to a positive value of 1.4

however, based on tests i did opening a simple 3d model of a plane with
positive, and then negative uv coordinates, it seems like the negative sign
is actually flipping the texture around the u/v axis.  is this correct?

thanks