From e415b17c019a15ab1924500eb14fa946b5c64e69 Mon Sep 17 00:00:00 2001
From: nicoo <nicoo@debian.org>
Date: Thu, 25 Jun 2020 05:05:31 +0200
Subject: [PATCH 1/3] factor::miller_rabin: Remove duplicated work

The duplicate work was introduced in 2015.
---
 src/uu/factor/src/miller_rabin.rs | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/src/uu/factor/src/miller_rabin.rs b/src/uu/factor/src/miller_rabin.rs
index 762ee1b4c..49099d5f1 100644
--- a/src/uu/factor/src/miller_rabin.rs
+++ b/src/uu/factor/src/miller_rabin.rs
@@ -54,7 +54,7 @@ pub(crate) fn test<A: Arithmetic + Basis>(m: A) -> Result {
     let one = m.one();
     let minus_one = m.minus_one();
 
-    for _a in A::BASIS.iter() {
+    'witness: for _a in A::BASIS.iter() {
         let _a = _a % n;
         if _a == 0 {
             continue;
@@ -65,22 +65,11 @@ pub(crate) fn test<A: Arithmetic + Basis>(m: A) -> Result {
         // x = a^r mod n
         let mut x = m.pow(a, r);
 
-        {
-            // y = ((x²)²...)² i times = x ^ (2ⁱ) = a ^ (r 2ⁱ) = x ^ (n - 1)
-            let mut y = x;
-            for _ in 0..i {
-                y = m.mul(y, y)
-            }
-            if y != one {
-                return Pseudoprime;
-            };
-        }
-
         if x == one || x == minus_one {
             continue;
         }
 
-        loop {
+        for _ in 1..i {
             let y = m.mul(x, x);
             if y == one {
                 return Composite(gcd(m.to_u64(x) - 1, m.modulus()));
@@ -88,10 +77,12 @@ pub(crate) fn test<A: Arithmetic + Basis>(m: A) -> Result {
             if y == minus_one {
                 // This basis element is not a witness of `n` being composite.
                 // Keep looking.
-                break;
+                continue 'witness;
             }
             x = y;
         }
+
+        return Pseudoprime;
     }
 
     Prime

From ecc3e2db24eb7d30f1c42a2944a39aa7db3ebb92 Mon Sep 17 00:00:00 2001
From: nicoo <nicoo@debian.org>
Date: Fri, 17 Jul 2020 12:53:28 +0200
Subject: [PATCH 2/3] factor::miller_rabin::test: Minor readability improvement

---
 src/uu/factor/src/miller_rabin.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/uu/factor/src/miller_rabin.rs b/src/uu/factor/src/miller_rabin.rs
index 49099d5f1..ad454f1ac 100644
--- a/src/uu/factor/src/miller_rabin.rs
+++ b/src/uu/factor/src/miller_rabin.rs
@@ -73,8 +73,7 @@ pub(crate) fn test<A: Arithmetic + Basis>(m: A) -> Result {
             let y = m.mul(x, x);
             if y == one {
                 return Composite(gcd(m.to_u64(x) - 1, m.modulus()));
-            }
-            if y == minus_one {
+            } else if y == minus_one {
                 // This basis element is not a witness of `n` being composite.
                 // Keep looking.
                 continue 'witness;

From 3e55139c13a55c74b734681cac178ad195a36222 Mon Sep 17 00:00:00 2001
From: nicoo <nicoo@debian.org>
Date: Fri, 17 Jul 2020 12:54:37 +0200
Subject: [PATCH 3/3] factor::miller_rabbin::Result: Mark as #[must_use]

Ignoring a value of that type is a bug: they are only produced by
`miller_rabbin::test`, which is a pure, but expensive, function.

As such, an ignored value is always either a mistake, or an easy
optimisation opportunity (just remove the useless call to `test`).
---
 src/uu/factor/src/miller_rabin.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/uu/factor/src/miller_rabin.rs b/src/uu/factor/src/miller_rabin.rs
index ad454f1ac..3d12ead02 100644
--- a/src/uu/factor/src/miller_rabin.rs
+++ b/src/uu/factor/src/miller_rabin.rs
@@ -25,6 +25,7 @@ impl Basis for Montgomery<u32> {
 }
 
 #[derive(Eq, PartialEq)]
+#[must_use = "Ignoring the output of a primality test."]
 pub(crate) enum Result {
     Prime,
     Pseudoprime,