#include "printf.h"

typedef unsigned long long uint64_t;
typedef unsigned long uint32_t;
#define MTIME_BASE 0x0200BFF8

uint64_t read_mtime_atomic() {
  uint32_t upper1, lower, upper2;

  do {
    upper1 = *(uint32_t*)(MTIME_BASE + 4);
    lower = *(uint32_t*)(MTIME_BASE);
    upper2 = *(uint32_t*)(MTIME_BASE + 4);
  } while (upper1 != upper2); // Repeat if upper changed during the process

  return ((uint64_t)upper1 << 32) | lower;
}

uint32_t timediff_ms(uint64_t start, uint64_t end) {
  uint64_t total = end-start;
  // Clock rate is currently 1MHz
  return (uint32_t)total / 1000;
}

int fib(int n) {
  if (n == 0 || n == 1)
    return 1;

  return fib(n-1) + fib(n-2);
}

int main() {
  int n = 24;
  uint64_t start = read_mtime_atomic();
  int res = fib(n);
  uint64_t end = read_mtime_atomic();
  uint32_t total_msec = timediff_ms(start, end);

  printf("fib(%d) = %d\n", n, res);
  printf("time: %dms\n", total_msec);
  return 0;
}