rand.rs

/*
 * Rust has no APIs for random numbers. At all! If you want that you have 
 * to rely on 3rd party libraries. This is simply ridiculous. Relying on 
 * 3rd party libraries for cryptographically strong random numbers is one
 * thing, however, there are many instances where you need a random number
 * that doesn't have to be cryptographically strong, and any modern 
 * programming environment (or even not so modern) should offer this,
 * Without having to rely on a 3rd party library!!!
 * 
 * Because rust doesn't offer it, we'll just have to build our own. We'll
 * do so by implementing a pretty standard unix srand/rand/rand_r LCNG. 
 */

static mut RAND_NEXT: u64 = 1;

#[no_mangle]
fn srand(s: u32) {
	// unsafe because writing globals in rust is considered unsafe ...
	unsafe {
		RAND_NEXT = s as u64;
	}
}

#[no_mangle]
fn rand_r(seed: &mut u64) -> u32 {
	*seed = *seed * 1103515245 + 12345;
	let r : u32 = ((*seed / 0x100000000) % 0x80000000) as u32;
	return r;
}

#[no_mangle]
fn rand() -> u32 {
	let r : u32;
	unsafe {
		r = rand_r(&mut RAND_NEXT);
	}
	return r;
}

#[no_mangle]
fn do_rand() {
	let s : u32 = SystemTime::now()
				.duration_since(UNIX_EPOCH)
				.unwrap()
				.as_nanos() as u32;
	
	println!("seed: {}", s);
	srand(s);
	
	let r = rand();
	println!("random value: {}", r);		
}