Remove dependency on the rand crate.

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

6 files changed, 55 insertions, 61 deletions

diff --git a/.gitignore b/.gitignore
index 68d3d90..184be20 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 /target/
 **/*.rs.bk
+**/*.swp
 result
diff --git a/Cargo.lock b/Cargo.lock
index 3f203e5..e296d32 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -15,17 +15,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
-name = "getrandom"
-version = "0.2.10"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "be4136b2a15dd319360be1c07d9933517ccf0be8f16bf62a3bee4f0d618df427"
-dependencies = [
- "cfg-if",
- "libc",
- "wasi",
-]
-
-[[package]]
 name = "lazy_static"
 version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -38,42 +27,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4668fb0ea861c1df094127ac5f1da3409a82116a4ba74fca2e58ef927159bb3"
 
 [[package]]
-name = "ppv-lite86"
-version = "0.2.17"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b40af805b3121feab8a3c29f04d8ad262fa8e0561883e7653e024ae4479e6de"
-
-[[package]]
-name = "rand"
-version = "0.8.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
-dependencies = [
- "libc",
- "rand_chacha",
- "rand_core",
-]
-
-[[package]]
-name = "rand_chacha"
-version = "0.3.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
-dependencies = [
- "ppv-lite86",
- "rand_core",
-]
-
-[[package]]
-name = "rand_core"
-version = "0.6.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
-dependencies = [
- "getrandom",
-]
-
-[[package]]
 name = "sdl2"
 version = "0.35.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -100,7 +53,6 @@ dependencies = [
 name = "stallman-shooter"
 version = "1.0.0"
 dependencies = [
- "rand",
  "sdl2",
  "sdl2-sys",
 ]
@@ -110,9 +62,3 @@ name = "version-compare"
 version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "579a42fc0b8e0c63b76519a339be31bed574929511fa53c1a3acae26eb258f29"
-
-[[package]]
-name = "wasi"
-version = "0.11.0+wasi-snapshot-preview1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
diff --git a/Cargo.toml b/Cargo.toml
index aa916f1..68cd630 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,9 +3,6 @@ name = "stallman-shooter"
 version = "1.0.0"
 authors = ["Rose Hogenson <rosehogenson@posteo.net>"]
 
-[dependencies]
-rand = "0.8.5"
-
 [dependencies.sdl2]
 version = "0.35.2"
 default-features = false
diff --git a/src/gates.rs b/src/gates.rs
index ebc2b69..1e3630f 100644
--- a/src/gates.rs
+++ b/src/gates.rs
@@ -1,4 +1,5 @@
 use super::constants;
+use super::rand;
 use super::state;
 
 pub struct Gates {
@@ -57,8 +58,8 @@ impl state::Positioned for Gates {
 
 fn random_position() -> (f64, f64) {
     (
-        rand::random::<f64>() * (constants::X_DIM - 200) as f64 + 100.,
-        rand::random::<f64>() * 100.,
+        rand::random() * (constants::X_DIM - 200) as f64 + 100.,
+        rand::random() * 100.,
     )
 }
 
@@ -85,8 +86,7 @@ impl state::StraightBullet for GatesBullet {
 
 fn random_bullet<T: state::Enemy<GatesBullet>>(enemy: &T) -> GatesBullet {
     let multiplier = 2. + 3. * (1. - enemy.health());
-    let theta: f64 =
-        rand::random::<f64>() * 2. * std::f64::consts::PI / 3. + std::f64::consts::PI / 6.;
+    let theta: f64 = rand::random() * 2. * std::f64::consts::PI / 3. + std::f64::consts::PI / 6.;
     let dx = f64::cos(theta) * multiplier;
     let dy = f64::sin(theta) * multiplier;
     GatesBullet::new(enemy.x(), dx, enemy.y(), dy)
diff --git a/src/main.rs b/src/main.rs
index 59913c0..25a4f3b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,7 @@
 mod constants;
 mod gates;
 mod player;
+mod rand;
 mod state;
 
 use state::Bullet;
@@ -221,6 +222,8 @@ fn victory(
 }
 
 fn main() {
+    rand::seed().expect("failed to seed random generator");
+
     let sdl_context = sdl2::init().unwrap();
     let video_subsystem = sdl_context.video().unwrap();
 
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.;
+}