#!/bin/bash

rm -f a.out
gcc -x c - <<EOF
#include <stdio.h>
#include <stdint.h>

unsigned long i;
uint32_t prev_pid_time;

unsigned long Gettime(void) { return i; }
uint8_t f() { return Gettime() - prev_pid_time; }

#define valid(a,b,c) \
  i=b;prev_pid_time=a; \
  printf("f(%3i,%3i)=%4i", a,b,f()); \
  if(f()!=c) printf("<>%-3i - fail", c); \
  else       printf("==%-3i", c); \
  printf("\n");

int main() {
  valid(  0, 2,   2);
  valid(  2, 2,   0);
  valid(  3, 2, 255);
  valid(255, 2,   3);
  valid(254, 0,   2);
  return 0;
}
EOF
./a.out