[R-SIG-Finance] returns convention

[paul sorenson]

Is it usually assumed that references to "returns" are calculated as 
diff(log(prices))?  Compared with say the simple fractional change from 
one price to the next?

For example, in PerformanceAnalytics I notice that the default value of 
CalculateReturns is diff(log(prices)).

I guess it probably doesn't matter much either way for small changes, I 
just wanted to know if there was some common convention when I see an R 
function that expects a returns vector.

cheers