refactor: change fast_random from xorshift to siphash a counter

Author: seanmonstar

src/util.rs

@@ -24,40 +24,26 @@ where
     header
 }
 
-// xor-shift
 #[cfg(not(target_arch = "wasm32"))]
 pub(crate) fn fast_random() -> u64 {
     use std::cell::Cell;
     use std::collections::hash_map::RandomState;
     use std::hash::{BuildHasher, Hasher};
-    use std::num::Wrapping;
 
     thread_local! {
-        static RNG: Cell<Wrapping<u64>> = Cell::new(Wrapping(seed()));
+        static KEY: RandomState = RandomState::new();
+        static COUNTER: Cell<u64> = Cell::new(0);
     }
 
-    fn seed() -> u64 {
-        let seed = RandomState::new();
+    KEY.with(|key| {
+        COUNTER.with(|ctr| {
+            let n = ctr.get().wrapping_add(1);
+            ctr.set(n);
 
-        let mut out = 0;
-        let mut cnt = 0;
-        while out == 0 {
-            cnt += 1;
-            let mut hasher = seed.build_hasher();
-            hasher.write_usize(cnt);
-            out = hasher.finish();
-        }
-        out
-    }
-
-    RNG.with(|rng| {
-        let mut n = rng.get();
-        debug_assert_ne!(n.0, 0);
-        n ^= n >> 12;
-        n ^= n << 25;
-        n ^= n >> 27;
-        rng.set(n);
-        n.0.wrapping_mul(0x2545_f491_4f6c_dd1d)
+            let mut h = key.build_hasher();
+            h.write_u64(n);
+            h.finish()
+        })
     })
 }