1 files changed, 95 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/util/rand.rs b/third_party/rust/tokio/src/util/rand.rs
new file mode 100644
index 0000000000..d96c8d37e0
--- /dev/null
+++ b/third_party/rust/tokio/src/util/rand.rs
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+cfg_rt! {
+    mod rt;
+    pub(crate) use rt::RngSeedGenerator;
+
+    cfg_unstable! {
+        mod rt_unstable;
+    }
+}
+
+/// A seed for random number generation.
+///
+/// In order to make certain functions within a runtime deterministic, a seed
+/// can be specified at the time of creation.
+#[allow(unreachable_pub)]
+#[derive(Clone, Debug)]
+pub struct RngSeed {
+    s: u32,
+    r: u32,
+}
+
+/// Fast random number generate.
+///
+/// Implement xorshift64+: 2 32-bit xorshift sequences added together.
+/// Shift triplet `[17,7,16]` was calculated as indicated in Marsaglia's
+/// Xorshift paper: <https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf>
+/// This generator passes the SmallCrush suite, part of TestU01 framework:
+/// <http://simul.iro.umontreal.ca/testu01/tu01.html>
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct FastRand {
+    one: u32,
+    two: u32,
+}
+
+impl RngSeed {
+    /// Creates a random seed using loom internally.
+    pub(crate) fn new() -> Self {
+        Self::from_u64(crate::loom::rand::seed())
+    }
+
+    fn from_u64(seed: u64) -> Self {
+        let one = (seed >> 32) as u32;
+        let mut two = seed as u32;
+
+        if two == 0 {
+            // This value cannot be zero
+            two = 1;
+        }
+
+        Self::from_pair(one, two)
+    }
+
+    fn from_pair(s: u32, r: u32) -> Self {
+        Self { s, r }
+    }
+}
+
+impl FastRand {
+    /// Initialize a new fast random number generator using the default source of entropy.
+    pub(crate) fn new() -> FastRand {
+        FastRand::from_seed(RngSeed::new())
+    }
+
+    /// Initializes a new, thread-local, fast random number generator.
+    pub(crate) fn from_seed(seed: RngSeed) -> FastRand {
+        FastRand {
+            one: seed.s,
+            two: seed.r,
+        }
+    }
+
+    #[cfg(any(
+        feature = "macros",
+        feature = "rt-multi-thread",
+        all(feature = "sync", feature = "rt")
+    ))]
+    pub(crate) fn fastrand_n(&mut self, n: u32) -> u32 {
+        // This is similar to fastrand() % n, but faster.
+        // See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+        let mul = (self.fastrand() as u64).wrapping_mul(n as u64);
+        (mul >> 32) as u32
+    }
+
+    fn fastrand(&mut self) -> u32 {
+        let mut s1 = self.one;
+        let s0 = self.two;
+
+        s1 ^= s1 << 17;
+        s1 = s1 ^ s0 ^ s1 >> 7 ^ s0 >> 16;
+
+        self.one = s0;
+        self.two = s1;
+
+        s0.wrapping_add(s1)
+    }
+}