Testing with unsigned int

uint.c

#include <stdio.h>

unsigned int sub(unsigned int previous, unsigned int next)
{
  unsigned int res = 0xffffffff;
  unsigned int diff = (next - previous);
  res += diff;

  res += 1;
  // This code performs the following
  // res = res + 0 + Cary_flag
  // Cary_Flag is set by the last arithmatic instruction
  // if res = res + diff resulted in an overflow Cary_flag will be 1

#if 0
  __asm__ __volatile__("adc %%ebx, %%eax"
                      :"=a" (res)
                      :"a"(res), "b"(0)
      );
#endif
  return (res);
}

int check_equal(unsigned int expected, unsigned int actual)
{
  if (expected != actual){
    printf ("check failed!, expected=%x, actual=%x\n", expected, actual);
    return (1);
  }

  return (0);
}

int main(int argc, char* argv[])
{
  unsigned int prev;
  unsigned int next;
  unsigned int res;
  unsigned int expected;

  prev = 20; next = 21;
  expected = 1;
  res = sub(prev, next);
  printf("prev=%u, next=%u, sub=%u, %x\n",prev, next, res, res);
  prev = 21; next = 20;
  check_equal(expected, res);
  // this is a complete roll over
  expected = 0xffffffff;
  res = sub(prev, next);
  printf("prev=%u, next=%u, sub=%u, %x\n",prev, next, res, res);
  check_equal(expected, res);

  return (0);
}