From 3b11af13d0f100c40a80a5e40251acae5358bfbc Mon Sep 17 00:00:00 2001
From: Sam Hadow <sam.hadow@proton.me>
Date: Tue, 7 Apr 2026 11:46:34 +0200
Subject: [PATCH] parallelize longest period finder

---
 Cargo.lock    | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++
 Cargo.toml    |  1 +
 src/main.rs   |  4 ++--
 src/period.rs | 17 ++++++++++++++++
 4 files changed, 74 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 07b92cf..2b8a5a0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,60 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9dd111b7b7f7d55b72c0a6ae361660ee5853c9af73f70c3c2ef6858b950e2e51"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.8.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
+
+[[package]]
+name = "either"
+version = "1.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
+
+[[package]]
+name = "rayon"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368f01d005bf8fd9b1206fb6fa653e6c4a81ceb1466406b81792d87c5677a58f"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22e18b0f0062d30d4230b2e85ff77fdfe4326feb054b9783a3460d8435c8ab91"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "tea-3"
 version = "0.1.0"
+dependencies = [
+ "rayon",
+]
diff --git a/Cargo.toml b/Cargo.toml
index d415757..71b0c40 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+rayon = "1.11.0"
diff --git a/src/main.rs b/src/main.rs
index dec652e..cca4e1d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,7 +3,7 @@ mod period;
 mod tea3;
 
 use lfsr::Lfsr;
-use period::{longest_period, period_bruteforce, period_floyd, period_paper};
+use period::{longest_period_parallel, period_bruteforce, period_floyd, period_paper};
 use tea3::Tea3;
 
 fn main() {
@@ -65,7 +65,7 @@ fn main() {
     // println!("\nPaper period p20: {}", period_paper(vec![0x7a, 0x02, 0x00, 0x00, 0x00]));
     // println!("\nPaper period p27: {}", period_paper(vec![0x00, 0x00, 0x00, 0x00, 0x00]));
 
-    let (p, seed) = longest_period();
+    let (p, seed) = longest_period_parallel();
     println!("\nLongest period: {}", p);
     println!("Seed: {:02x?}", seed);
 }
diff --git a/src/period.rs b/src/period.rs
index b6c18c8..ab6b138 100644
--- a/src/period.rs
+++ b/src/period.rs
@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use rayon::prelude::*;
 
 use crate::tea3::Tea3;
 
@@ -177,3 +178,19 @@ pub fn longest_period() -> (u64, [u8; 5]) {
 
     (best_period, best_seed)
 }
+
+pub fn longest_period_parallel() -> (u64, [u8; 5]) {
+    let limit: usize = 1usize << 40;
+
+    (0usize..limit)
+        .into_par_iter()
+        .map(|x| {
+            let seed = Reg5::from_u40(x as u64);
+            let p = period_h(seed);
+            (p, seed.0)
+        })
+        .reduce(
+            || (0u64, [0u8; 5]),
+            |a, b| if a.0 >= b.0 { a } else { b },
+        )
+}