Fibonacci

#include <stdio.h>
#include <sys/time.h>
#include <time.h>
static unsigned long long fib(unsigned);
static void initialize_memoize(void);
static unsigned long long memoize_fib(unsigned);
static unsigned long long accumulate_fib(unsigned);
static unsigned long long accumulate_fib_sub(unsigned, unsigned long long, unsigned long long);
static double diff_time(clock_t, clock_t);
void puts_fib(unsigned long long (*)(unsigned), unsigned);
int main(void);
static unsigned long long fib(unsigned n) {
  if (n < 2) return 1;
  return fib(n - 1) + fib(n - 2);
}
static unsigned long long memo_fib[BUFSIZ];
static void initialize_memoize(void) {
  int i;
  for (i = 0; i < BUFSIZ; i++)
    memo_fib[i] = 0;
  memo_fib[0] = 1;
  memo_fib[1] = 1;
}
static unsigned long long memoize_fib(unsigned n) {
  unsigned long long pre1, pre2;
  if (n < 0) return 0;
  if (memo_fib[n - 1])
    pre1 = memo_fib[n - 1];
  else
    pre1 = memo_fib[n - 1] = memoize_fib(n - 1);
  if (memo_fib[n - 2])
    pre2 = memo_fib[n - 2];
  else
    pre2 = memo_fib[n - 2] = memoize_fib(n - 2);
  return pre1 + pre2;
}
static unsigned long long accumulate_fib(unsigned n) {
  return accumulate_fib_sub(n, 1, 1);
}
static unsigned long long accumulate_fib_sub(unsigned n, unsigned long long a, unsigned long long b) {
  if (n < 1) return a;
  return accumulate_fib_sub(n - 1, b, a + b);
}
static double diff_time(clock_t start, clock_t stop) {
  return (double) (stop - start) / CLOCKS_PER_SEC;
}
void puts_fib(unsigned long long (*fib_func)(unsigned), unsigned n) {
  clock_t start, stop;
  unsigned long long f;
  start = clock();
  f = fib_func(n);
  stop = clock();
  printf("fib(%4d) = %lld\t[%.3lf sec.]\n", n, f, diff_time(start, stop));
}
int main(void) {
  puts_fib(fib, 40);
  initialize_memoize();
  puts_fib(memoize_fib, BUFSIZ - 1);
  puts_fib(accumulate_fib, BUFSIZ - 1);
  return 0;
}