From 92c73fb12520b2c208c345bfdf0540d3e10b99c1 Mon Sep 17 00:00:00 2001
From: Felix Martin <mail@felixm.de>
Date: Thu, 4 Aug 2022 17:13:38 -0400
Subject: [PATCH] Challenge 23 eod.

---
 src/main.rs    |  2 +-
 src/mt19937.rs | 14 +++++++----
 src/set3.rs    | 64 +++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 73 insertions(+), 7 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 3f5816a..d9fc37a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,7 +10,7 @@ mod set2;
 mod set3;
 
 fn main() {
-    const RUN_ALL: bool = true;
+    const RUN_ALL: bool = false;
     if RUN_ALL {
         set1::challenge1();
         set1::challenge2();
diff --git a/src/mt19937.rs b/src/mt19937.rs
index ffa8170..c5ca01a 100644
--- a/src/mt19937.rs
+++ b/src/mt19937.rs
@@ -18,8 +18,12 @@ impl MT19937 {
         mt
     }
 
+    pub fn splice(&mut self, state: Vec<u32>) {
+        self.mt = state;
+        self.index = 624;
+    }
+
     pub fn seed(&mut self, seed: u32) {
-        self.index = N;
         const F: u32 = 1812433253;
         self.mt[0] = seed;
         for i in 1..N {
@@ -27,14 +31,14 @@ impl MT19937 {
                 + Wrapping(i as u32))
             .0;
         }
+        self.twist();
     }
 
     pub fn extract_number(&mut self) -> u32 {
-        if self.index >= N {
-            if self.index > N {
-                panic!("Generator was never seeded");
-            }
+        if self.index == N {
             self.twist();
+        } else if self.index > N {
+            panic!("Generator was never seeded");
         }
 
         const S: u32 = 7;
diff --git a/src/set3.rs b/src/set3.rs
index 8180867..e6ced6f 100644
--- a/src/set3.rs
+++ b/src/set3.rs
@@ -359,5 +359,67 @@ pub fn challenge22() {
 }
 
 pub fn challenge23() {
-    println!("[xxxx] Challenge 23: tbd");
+    // Once you have "untemper" working, create a new MT19937 generator, tap it for 624 outputs,
+    /*
+    let mut mt = mt19937::MT19937::new();
+    let seed: u32 = rand::thread_rng().gen::<u32>();
+    mt.seed(seed);
+    let outputs: Vec<u32> = (0..624).map(|_| mt.extract_number()).collect();
+    */
+
+    fn temper(x: u32) -> u32 {
+        //const S: u32 = 7;
+        //const T: u32 = 15;
+        //const U: u32 = 11;
+        //const B: u32 = 0x9D2C5680;
+        //const C: u32 = 0xEFC60000;
+        //const L: u32 = 18;
+
+        let mut y = x;
+        // y = y ^ (y >> U);
+        // y = y ^ ((y << S) & B);
+        // y = y ^ ((y << T) & C);
+        // y = y ^ (y >> L);
+        y = y ^ (y >> 24);
+        y
+    }
+
+    fn untemper(x: u32) -> u32 {
+        //const S: u32 = 7;
+        //const T: u32 = 15;
+        //const U: u32 = 11;
+        //const B: u32 = 0x9D2C5680;
+        //const C: u32 = 0xEFC60000;
+        //const L: u32 = 18;
+
+        let mut y = x;
+        //y = y ^ (y >> U);
+        //y = y ^ ((y << S) & B);
+        //y = y ^ ((y << T) & C);
+        //y = y ^ (y >> L);
+
+        //  xxxx'yyyy
+        // ^0000'xxxx
+        //  xxxx'zzzz
+        println!("{:#010x}", u32::MAX << 11 );
+        y = (y & 0xffffff00) | (((y & 0xff000000) >> 24) ^ (y & 0x000000ff));
+        y
+    }
+
+    let a: u32 = 0x12345678;
+    let b = temper(a);
+    let c = untemper(b);
+    println!("{:#010x} -> {:#010x} -> {:#010x}", a, b, c);
+
+    /*
+    // untemper each of them to recreate the state of the generator,
+    let outputs = outputs.iter().map(|o| untemper(*o)).collect();
+
+    //and splice that state into a new instance of the MT19937 generator.
+    let mut new_mt = mt19937::MT19937::new();
+    new_mt.splice(outputs);
+    println!("{} {}", mt.extract_number(), new_mt.extract_number());
+    */
+
+    println!("[xxxx] Challenge 23: wip");
 }