if vs. switch

Comparing if/else with switch

This example shows how a compiler may be able to optimize a switch statement better than if/else. Below is a sample, but with many more cases, the times are just getting worse. The program doesn't actually do anything useful, but it does demonstrate the difference in performance between the two constructs.

The program did 400,000,000 iterations for each value, from 1 to 33, which includes all of the if/else and switch cases and one value that is out of range (for the else or default).

if/elseswitch
int sw4a(int a)
{
  if (a == 1)
  {
    return a;
  }
  else if (a == 2)
  {
    return 7 * a;
  }
  else if (a == 3)
  {
    return 6 * a;
  }
  else if (a == 4)
  {
    return 5 * a;
  }
  else if (a == 5)
  {
    return 4 * a;
  }
  else if (a == 6)
  {
    return 3 * a;
  }
  else if (a == 7)
  {
    return 2 * a;
  }
  else if (a == 8)
  {
    return 3 * a;
  }
  else if (a == 9)
  {
    return 4 * a;
  }
  else if (a == 10)
  {
    return 5 * a;
  }
  else if (a == 11)
  {
    return 6 * a;
  }
  else if (a == 12)
  {
    return 7 * a;
  }
  else if (a == 13)
  {
    return 6 * a;
  }
  else if (a == 14)
  {
    return 5 * a;
  }
  else if (a == 15)
  {
    return 4 * a;
  }
  else if (a == 16)
  {
    return 3 * a;
  }
  else if (a == 17)
  {
    return 3 * a;
  }
  else if (a == 18)
  {
    return 3 * a;
  }
  else if (a == 19)
  {
    return 3 * a;
  }
  else if (a == 20)
  {
    return 3 * a;
  }
  else if (a == 21)
  {
    return 4 * a;
  }
  else if (a == 22)
  {
    return 3 * a;
  }
  else if (a == 23)
  {
    return 5 * a;
  }
  else if (a == 24)
  {
    return 3 * a;
  }
  else if (a == 25)
  {
    return 6 * a;
  }
  else if (a == 26)
  {
    return 3 * a;
  }
  else if (a == 27)         
  {
    return 7 * a;
  }
  else if (a == 28)
  {
    return 3 * a;
  }
  else if (a == 29)
  {
    return 8 * a;
  }
  else if (a == 30)
  {
    return 3 * a;
  }
  else if (a == 31)
  {
    return 7 * a;
  }
  else if (a == 32)
  {
    return 3 * a;
  }
  else 
    return 5 * a;
}

int sw4b(int a)
{
  switch (a)
  {
    case 1:
      return 5 * a;
      break;
    case 2:
      return 4 * a;
      break;
    case 3:
      return 3 * a;
      break;
    case 4:
      return 2 * a;
      break;
    case 5:
      return 4 * a;
      break;
    case 6:
      return 5 * a;
      break;
    case 7:
      return 6 * a;
      break;
    case 8:
      return 7 * a;
      break;
    case 9:
      return 8 * a;
      break;
    case 10:
      return 7 * a;
      break;
    case 11:
      return 6 * a;
      break;
    case 12:
      return 5 * a;
      break;
    case 13:
      return 4 * a;
      break;
    case 14:
      return 3 * a;
      break;
    case 15:
      return 2 * a;
      break;
    case 16:
      return 3 * a;
      break;
    case 17:
      return 4 * a;
      break;
    case 18:
      return 3 * a;
      break;
    case 19:
      return 2 * a;
      break;
    case 20:
      return 8 * a;
      break;
    case 21:
      return 3 * a;
      break;
    case 22:
      return 7 * a;
      break;
    case 23:
      return 3 * a;
      break;
    case 24:
      return 6 * a;
      break;
    case 25:
      return 3 * a;
      break;
    case 26:
      return 5 * a;
      break;
    case 27:
      return 3 * a;
      break;
    case 28:
      return 4 * a;
      break;
    case 29:
      return 3 * a;
      break;
    case 30:
      return 7 * a;
      break;
    case 31:
      return 3 * a;
      break;
    case 32:
      return 6 * a;
      break;
    default:
      return 4 * a;
  }
}

Output:

if/elseswitch
Value is 01: Time:  6.902
Value is 02: Time:  7.014
Value is 03: Time:  7.405
Value is 04: Time:  7.560
Value is 05: Time:  7.743
Value is 06: Time:  8.076
Value is 07: Time:  8.209
Value is 08: Time:  8.442
Value is 09: Time:  8.573
Value is 10: Time:  8.858
Value is 11: Time:  9.296
Value is 12: Time:  9.328
Value is 13: Time:  9.631
Value is 14: Time: 10.055
Value is 15: Time: 10.134
Value is 16: Time: 10.397
Value is 17: Time: 10.522
Value is 18: Time: 10.805
Value is 19: Time: 11.376
Value is 20: Time: 11.314
Value is 21: Time: 11.539
Value is 22: Time: 11.947
Value is 23: Time: 11.971
Value is 24: Time: 12.024
Value is 25: Time: 12.242
Value is 26: Time: 12.349
Value is 27: Time: 12.634
Value is 28: Time: 12.797
Value is 29: Time: 13.164
Value is 30: Time: 13.235
Value is 31: Time: 13.676
Value is 32: Time: 13.750
Value is 33: Time: 13.812         

Value is 01: Time: 7.100
Value is 02: Time: 6.970
Value is 03: Time: 7.105
Value is 04: Time: 6.995
Value is 05: Time: 6.969
Value is 06: Time: 7.094
Value is 07: Time: 6.972
Value is 08: Time: 7.193
Value is 09: Time: 6.969
Value is 10: Time: 6.961
Value is 11: Time: 6.969
Value is 12: Time: 7.012
Value is 13: Time: 7.071
Value is 14: Time: 6.970
Value is 15: Time: 7.076
Value is 16: Time: 6.974
Value is 17: Time: 7.078
Value is 18: Time: 7.092
Value is 19: Time: 6.980
Value is 20: Time: 6.970
Value is 21: Time: 7.062
Value is 22: Time: 6.968
Value is 23: Time: 7.068
Value is 24: Time: 6.988
Value is 25: Time: 7.067
Value is 26: Time: 7.200
Value is 27: Time: 7.214
Value is 28: Time: 6.974
Value is 29: Time: 7.086
Value is 30: Time: 6.970
Value is 31: Time: 6.961
Value is 32: Time: 7.085
Value is 33: Time: 6.657