[kzrdude]

Depends on how you define speed-up. This is the most natural definition for me:

As a baseline, my code can do 100 operations / second.

With 50% speedup (+50%), my code can do 150 operations / second.

If C was 40x faster than the baseline, it could do 4000 operations / second. After the speedup C can still do 27x as many operations per second. (4000/150 = 26.66..)

[nequo]

Well, that’s true. The good old miles per gallon vs. liters per 100 kilometers conundrum.