Sexy 'multi-ramp' needs Optimisation (was 'conditionals in jit.expr')

Hey, I am subverting my own thread (with the help of Alex) like the good old email lists allowed us to do ;-)

So here we are, I'd like to clean that jit.expr as it is ugly and inefficient, but as jit.expr does not allow conditionals, I am trying to fiddle around...

For the curious, it is a set of independent ramps. The following example has only 100 to see it work, but make it with a couple of thousand and it is beautiful ;-)