Implement MT19937 for challenge 21.

src/set3.rs

@@ -2,6 +2,7 @@ use crate::bytes::Bytes;
 use crate::bytes_base64::BytesBase64;
 use crate::cbc;
 use crate::ctr;
+use crate::mt19937;
 use rand::Rng;
 use std::cell::RefCell;
 use std::collections::HashMap;
@@ -301,5 +302,20 @@ pub fn challenge20() {
 }
 
 pub fn challenge21() {
-    println!("[xxxx] Challenge 21: TBD");
+    // Implement the MT19937 Mersenne Twister RNG
+
+    let expected: Vec<u32> = vec![
+        0xD091BB5C, 0x22AE9EF6, 0xE7E1FAEE, 0xD5C31F79, 0x2082352C, 0xF807B7DF, 0xE9D30005,
+        0x3895AFE1, 0xA1E24BBA, 0x4EE4092B,
+    ];
+    let mut mt = mt19937::MT19937::new();
+    mt.seed(5489);
+    for i in 0..expected.len() {
+        assert_eq!(mt.extract_number(), expected[i]);
+    }
+    println!("[okay] Challenge 21: Implemented MT19937");
+}
+
+pub fn challenge22() {
+    println!("[xxxx] Challenge 22: TBD!");
 }