Thank you and Merci Antoine!

That is a good point.  It is clearly specific to the compiler whether a 
switch-case will be turned into a series of conditional branches or 
simply creating an internal jump table with lookup.  And it is true 
that most compilers, if I understand correctly, use the jump-table 
approach for any switch-case over 2 or 3 entries when the cases are 
tightly grouped and near 0.  That is probably why the original code 
worked so fast.  I'll see if I can combine the best of both 
approaches.  Thanks again!