Switch statement with huge number of cases

Question

What happens if the switch has more than 5000 case. What are the drawbacks and how we can replace it with something faster?

Note: I am not expe

Answer 1

Big switch statement, generally auto-generated one, may take long time to compile. But I like the idea that compiler optimizes the switch statement.

One way to break apart the switch statement is to use bucketing,

int getIt(int input)
{
  int bucket = input%16;
  switch(bucket)
  {
    case 1:
      return getItBucket1(input);
    case 2:
      return getItBucket2(input);
    ...
    ...
  }
  return -1;
}

So in the code above, we broke apart our switch statement into 16 parts. It is easy to change the number of buckets in auto-generated code.

This code has added run-time cost of one layer of indirection or function-call. . But considering the buckets defined in different files, it is faster to compile them in parallel.