Is it more efficient to perform a range check by casting to uint instead of checking for negative values?

Question

I stumbled upon this piece of code in .NET\'s List source code:

// Following trick can reduce the range check by one
if ((uint) index >= (uint)_size) {
           


        

Answer 1

While exploring this on an intel processor I found no differene in execution times, possibly due to multiple integer execution units.

But when doing this on 16MHZ real-time microprocessor with neither branch prediction nor integer execution units there were notable differences.

1 million iterations of the slower code took 1761 ms

int slower(char *a, long i)
{
  if (i < 0 || i >= 10)
    return 0;

  return a[i];
}

1 million iterations faster code took 1635 ms

int faster(char *a, long i)
{
  if ((unsigned int)i >= 10)
    return 0;
  return a[i];
}