1 files changed, 81 insertions, 0 deletions
diff --git a/third_party/rust/neqo-transport/tests/sim/rng.rs b/third_party/rust/neqo-transport/tests/sim/rng.rs
new file mode 100644
index 0000000000..af4f70eb5f
--- /dev/null
+++ b/third_party/rust/neqo-transport/tests/sim/rng.rs
@@ -0,0 +1,81 @@
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::{convert::TryFrom, ops::Range};
+
+use neqo_common::Decoder;
+
+/// An implementation of a xoshiro256** pseudorandom generator.
+pub struct Random {
+    state: [u64; 4],
+}
+
+impl Random {
+    pub fn new(seed: [u8; 32]) -> Self {
+        assert!(seed.iter().any(|&x| x != 0));
+        let mut dec = Decoder::from(&seed);
+        Self {
+            state: [
+                dec.decode_uint(8).unwrap(),
+                dec.decode_uint(8).unwrap(),
+                dec.decode_uint(8).unwrap(),
+                dec.decode_uint(8).unwrap(),
+            ],
+        }
+    }
+
+    pub fn random(&mut self) -> u64 {
+        let result = (self.state[1].overflowing_mul(5).0)
+            .rotate_right(7)
+            .overflowing_mul(9)
+            .0;
+        let t = self.state[1] << 17;
+
+        self.state[2] ^= self.state[0];
+        self.state[3] ^= self.state[1];
+        self.state[1] ^= self.state[2];
+        self.state[0] ^= self.state[3];
+
+        self.state[2] ^= t;
+        self.state[3] = self.state[3].rotate_right(45);
+
+        result
+    }
+
+    /// Generate a random value from the range.
+    /// If the range is empty or inverted (`range.start > range.end`), then
+    /// this returns the value of `range.start` without generating any random values.
+    pub fn random_from(&mut self, range: Range<u64>) -> u64 {
+        let max = range.end.saturating_sub(range.start);
+        if max == 0 {
+            return range.start;
+        }
+
+        let shift = (max - 1).leading_zeros();
+        assert_ne!(max, 0);
+        loop {
+            let r = self.random() >> shift;
+            if r < max {
+                return range.start + r;
+            }
+        }
+    }
+
+    /// Get the seed necessary to continue from this point.
+    pub fn seed_str(&self) -> String {
+        format!(
+            "{:8x}{:8x}{:8x}{:8x}",
+            self.state[0], self.state[1], self.state[2], self.state[3],
+        )
+    }
+}
+
+impl Default for Random {
+    fn default() -> Self {
+        let buf = neqo_crypto::random(32);
+        Random::new(<[u8; 32]>::try_from(&buf[..]).unwrap())
+    }
+}