1 files changed, 38 insertions, 0 deletions
diff --git a/third_party/rust/digest/src/dev/rng.rs b/third_party/rust/digest/src/dev/rng.rs
new file mode 100644
index 0000000000..d34a1cf31f
--- /dev/null
+++ b/third_party/rust/digest/src/dev/rng.rs
@@ -0,0 +1,38 @@
+//! Xorshift RNG used for tests. Based on the `rand_xorshift` crate.
+use core::num::Wrapping;
+
+/// Initial RNG state used in tests.
+// chosen by fair dice roll. guaranteed to be random.
+pub(crate) const RNG: XorShiftRng = XorShiftRng {
+    x: Wrapping(0x0787_3B4A),
+    y: Wrapping(0xFAAB_8FFE),
+    z: Wrapping(0x1745_980F),
+    w: Wrapping(0xB0AD_B4F3),
+};
+
+/// Xorshift RNG instance/
+pub(crate) struct XorShiftRng {
+    x: Wrapping<u32>,
+    y: Wrapping<u32>,
+    z: Wrapping<u32>,
+    w: Wrapping<u32>,
+}
+
+impl XorShiftRng {
+    pub(crate) fn fill(&mut self, buf: &mut [u8; 1024]) {
+        for chunk in buf.chunks_exact_mut(4) {
+            chunk.copy_from_slice(&self.next_u32().to_le_bytes());
+        }
+    }
+
+    fn next_u32(&mut self) -> u32 {
+        let x = self.x;
+        let t = x ^ (x << 11);
+        self.x = self.y;
+        self.y = self.z;
+        self.z = self.w;
+        let w = self.w;
+        self.w = w ^ (w >> 19) ^ (t ^ (t >> 8));
+        self.w.0
+    }
+}