#[no_mangle]
pub unsafe fn malloc_1(len: usize) -> *mut u8 {
    let mut buffer: std::mem::ManuallyDrop<Vec<u8>> = std::mem::ManuallyDrop::new(Vec::with_capacity(len as usize));
    buffer.as_mut_ptr() as *mut u8
}

#[no_mangle]
pub unsafe fn free_1(ptr: *mut u8, len: usize) {
    std::mem::drop(Vec::from_raw_parts(ptr as *mut u8, 0, len as usize))
}

#[no_mangle]
pub unsafe fn malloc_2(len: usize) -> *mut u8 {
    let mut buf = Vec::with_capacity(len);
    let ptr = buf.as_mut_ptr();
    std::mem::forget(buf);
    return ptr;
}

#[no_mangle]
pub unsafe fn free_2(ptr: *mut u8, len: usize) {
    let data = Vec::from_raw_parts(ptr, len, len);
    std::mem::drop(data);
}

#[no_mangle]
pub unsafe fn malloc_3(len: usize) -> *mut u8 {
    let align = std::mem::align_of::<usize>();
    let layout = std::alloc::Layout::from_size_align_unchecked(len, align);
    std::alloc::alloc(layout)
}

#[no_mangle]
pub unsafe fn free_3(ptr: *mut u8, len: usize) {
    let align = std::mem::align_of::<usize>();
    let layout = std::alloc::Layout::from_size_align_unchecked(len, align);
    std::alloc::dealloc(ptr, layout)
}

fn main() {
    unsafe {
        println!("Malloc & Free - 1");
        let p = malloc_1(1024);
        free_1(p, 1024);

        println!("Malloc & Free - 2");
        let p = malloc_2(1024);
        free_2(p, 1024);

        println!("Malloc & Free - 3");
        let p = malloc_3(1024);
        free_3(p, 1024);
    }
}