# Lab 2-1: Fibonacci
Reference [林霆寬Fibonacci](https://hackmd.io/pDfcdWwSQqmt3oXsHPXueA?view)
###### tags: `CA2020`

## Rewrite Fibonacci C Code
In the beginning, I used recursive C code. After I saw objdump, I found that it's too long.
When we comes to execution time, non-recursive C code is much better in this case. This is because we don't need stack.
So, the following C code is non-recursive Fibonacci.

#include<stdio.h>

void _start()
{
    int x;
    int temp = 0;
    int n = 0;
    int prev = 1;
    if (n <= 1)
     x = 1;

    for (n = 2;n<10;n++)
    {
       temp = x;
       x = x + prev;
       prev = temp;

    }
    volatile char* tx = (volatile char*) 0x40002000;
    int out = x;
    *tx = out;
}





riscv-none-embed-gcc -march=rv32i -mabi=ilp32 -O3 -nostdlib Fibonacci.c -o Fibonacci

In this code, there's no difference between -O3 and -Os.