If a switch is sparse and all the cases (once sorted) are in arithmetic progression, we can extract the common factor out of the switch and create a dense switch. For example:

switch (i) { case 5: ... case 9: ... case 13: ... case 17: ... }

can become:

if ( (i - 5) % 4 ) goto default; switch ((i - 5) / 4) { case 0: ... case 1: ... case 2: ... case 3: ... }

The division and remainder operations could be costly so we only do this if the factor is a power of two. Dense switches can be lowered significantly better than sparse switches and can even be transformed into lookup tables.