unsigned long long read_timer() { _asm { rdtsc } }

inline __int64 __fastcall RDTSC( )
{
  _asm{
    rdtsc
  }
}

void
GetTimeNT( u64* t )
{
    u32 lo, hi;

    // Read the Time-Stamp Counter register into 'lo' and 'hi.
    __asm
    {
        // If this is the Metrowerks compiler.
#ifdef __MWERKS__

        rdtsc

#else // Visual C++ Compiler doesn't recognize the 'rdtsc'
      // instruction so the opcodes are used instead.

        __emit  0fh
        __emit  031h
#endif
        mov   lo, eax
        mov   hi, edx
    }

    // Combine the low and high 32-bit parts into a single
    // 64-bit number and return the result.
    *t = ( (u64) hi << 32 ) | (u64) lo;
}

The value returned is a 64-bit counter that is incremented by the system clock. So on a 500 MHz Pentium II, each tick is 2 nS.  To use, do something like:

int
main(int argc, char **argv)
{
  __int64 t1, t2;
  long elapsed;

  /* start measurement */
  t1 = RDTSC();

  /* call code under test */
  foo();

  /* stop measurement */
  t2 = RDTSC();

  /* compute elapsed time in microseconds, 500 MHz CPU */
  elapsed = (long) ((t2 - t1)/500);

  return 0;
};

This is the email I got from him:

Your grade was: B Comments (if any) that you may find useful: "Good C code let down by lack of code comments and dubious testing. All three sorts have near-identical results, which is wrong. The report was a little short of information and analysis, though it's always nice to see Eric Cartman playing his part in computer science. Sorry about the mark but remember, ""you will respect my authoritaah!"""