From 11a8cb9e83eec6ee0f7f85b3593bcbe3c2248f61 Mon Sep 17 00:00:00 2001
From: Alula <julekonopinska@gmail.com>
Date: Sat, 5 Sep 2020 03:03:43 +0200
Subject: [PATCH] improved and fixed rng

---
 src/rng.rs | 42 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/src/rng.rs b/src/rng.rs
index 952f8b0..5d5bb62 100644
--- a/src/rng.rs
+++ b/src/rng.rs
@@ -1,23 +1,51 @@
 use std::cell::Cell;
 
-pub struct RNG(Cell<i32>);
+pub struct RNG(Cell<(u64, u64, u64, u64)>);
+
+fn rol64(x: u64, shift: u64) -> u64
+{
+    if shift == 0 || shift == 64 {
+        x
+    } else {
+        (x << shift) | (x >> (64 - shift))
+    }
+}
 
 impl RNG {
     pub fn new(seed: i32) -> Self {
-        Self(Cell::new(seed))
+        Self(Cell::new((seed as u64,
+                        (seed as u64).wrapping_add(0x9e3779b97f4a7c15),
+                        (seed as u64).wrapping_add(0xbdd3944475a73cf0),
+                        0
+        )))
+    }
+
+    pub fn next_u64(&self) -> i32 {
+        let mut state = self.0.get();
+        let result = rol64(state.1.wrapping_mul(5), 7).wrapping_mul(9);
+        let t = state.1 << 17;
+
+        state.2 ^= state.0;
+        state.3 ^= state.1;
+        state.1 ^= state.2;
+        state.0 ^= state.3;
+
+        state.2 ^= t;
+        state.3 = rol64(state.3, 45);
+
+        self.0.replace(state);
+        result as i32
     }
 
     pub fn next(&self) -> i32 {
-        // MSVC LCG values
-        self.0.replace(self.0.get().wrapping_mul(214013).wrapping_add(2531011));
-        self.0.get()
+        self.next_u64() as i32
     }
 
     pub fn next_u32(&self) -> u32 {
-        self.next() as u32
+        self.next_u64() as u32
     }
 
     pub fn range(&self, range: std::ops::Range<i32>) -> i32 {
-        range.start.wrapping_add(self.next() % (range.end.wrapping_sub(range.start).wrapping_add(1)))
+        range.start.wrapping_add((self.next_u32() >> 2) as i32 % (range.end.wrapping_sub(range.start).wrapping_add(1)))
     }
 }