Remove dependency on the rand crate.

I don't need a dependency to generate random numbers. I know how to
generate random numbers.

1 files changed, 47 insertions, 0 deletions

diff --git a/src/rand.rs b/src/rand.rs
new file mode 100644
index 0000000..404e115
--- /dev/null
+++ b/src/rand.rs
@@ -0,0 +1,47 @@
+use std::fs::File;
+use std::io::Read;
+use std::sync::Mutex;
+use std::time::SystemTime;
+
+static STATE: Mutex<u64> = Mutex::new(0);
+
+fn seed_urandom() -> Option<()> {
+    let mut f = File::open("/dev/urandom").ok()?;
+    let mut bytes = [0; 8];
+    f.read_exact(&mut bytes).ok()?;
+
+    *STATE.lock().unwrap() = u64::from_ne_bytes(bytes);
+    return Some(());
+}
+
+fn seed_time() -> Option<()> {
+    let n = SystemTime::now()
+        .duration_since(SystemTime::UNIX_EPOCH)
+        .ok()?;
+
+    *STATE.lock().unwrap() = n.as_nanos() as u64;
+    return Some(());
+}
+
+pub fn seed() -> Option<()> {
+    match seed_urandom() {
+        Some(()) => return Some(()),
+        None => (),
+    }
+    match seed_time() {
+        Some(()) => return Some(()),
+        None => (),
+    }
+    return None;
+}
+
+fn mix(s: &mut u64) {
+    // https://en.wikipedia.org/wiki/Linear_congruential_generator
+    *s = s.wrapping_mul(6364136223846793005).wrapping_add(1);
+}
+
+pub fn random() -> f64 {
+    let mut s = STATE.lock().unwrap();
+    mix(&mut s);
+    return (*s >> 32) as f64 / 4294967296.;
+}