From 34a5941ee9b5db59c2b76be5e107cfb8bb4cab0c Mon Sep 17 00:00:00 2001
From: nicoo <nicoo@debian.org>
Date: Mon, 3 Aug 2020 14:00:34 +0200
Subject: [PATCH] factor::numeric: Add more property-based tests (#1577)

* factor::numeric::gcd: Rename test against the Euclidean algorithm

* factor::numeric::gcd: Add various property-based tests

* factor::numeric::modular_inverse: Rename test

* factor::numeric::modular_inverse: Add test on random values
---
 src/uu/factor/src/numeric/gcd.rs             | 35 ++++++++++++++++++--
 src/uu/factor/src/numeric/modular_inverse.rs | 17 ++++++++--
 2 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/src/uu/factor/src/numeric/gcd.rs b/src/uu/factor/src/numeric/gcd.rs
index 54067c56e..0cde65472 100644
--- a/src/uu/factor/src/numeric/gcd.rs
+++ b/src/uu/factor/src/numeric/gcd.rs
@@ -51,7 +51,7 @@ mod tests {
     use quickcheck::quickcheck;
 
     quickcheck! {
-        fn gcd(a: u64, b: u64) -> bool {
+        fn euclidean(a: u64, b: u64) -> bool {
             // Test against the Euclidean algorithm
             let g = {
                 let (mut a, mut b) = (a, b);
@@ -61,7 +61,38 @@ mod tests {
                 }
                 a
             };
-            super::gcd(a, b) == g
+            gcd(a, b) == g
+        }
+
+        fn one(a: u64) -> bool {
+            gcd(1, a) == 1
+        }
+
+        fn divisor(a: u64, b: u64) -> bool {
+            // Test that gcd(a, b) divides a and b
+            let g = gcd(a, b);
+            a % g == 0 && b % g == 0
+        }
+
+        fn commutative(a: u64, b: u64) -> bool {
+            gcd(a, b) == gcd(b, a)
+        }
+
+        fn associative(a: u64, b: u64, c: u64) -> bool {
+            gcd(a, gcd(b, c)) == gcd(gcd(a, b), c)
+        }
+
+        fn scalar_mult(a: u64, b: u64, k: u64) -> bool {
+            gcd(k * a, k * b) == k * gcd(a, b)
+        }
+
+        fn multiplicative(a: u64, b: u64, c: u64) -> bool {
+            // gcd(ab, c) = gcd(a, c) gcd(b, c) when a and b coprime
+            gcd(a, b) != 1 || gcd(a * b, c) == gcd(a, c) * gcd(b, c)
+        }
+
+        fn linearity(a: u64, b: u64, k: u64) -> bool {
+            gcd(a + k * b, b) == gcd(a, b)
         }
     }
 }
diff --git a/src/uu/factor/src/numeric/modular_inverse.rs b/src/uu/factor/src/numeric/modular_inverse.rs
index 5310a1886..763ee90a0 100644
--- a/src/uu/factor/src/numeric/modular_inverse.rs
+++ b/src/uu/factor/src/numeric/modular_inverse.rs
@@ -47,8 +47,9 @@ pub(crate) fn modular_inverse<T: Int>(a: T) -> T {
 mod tests {
     use super::{super::traits::Int, *};
     use crate::parametrized_check;
+    use quickcheck::quickcheck;
 
-    fn test_inverter<T: Int>() {
+    fn small_values<T: Int>() {
         // All odd integers from 1 to 20 000
         let one = T::from(1).unwrap();
         let two = T::from(2).unwrap();
@@ -58,5 +59,17 @@ mod tests {
 
         assert!(test_values.all(|x| x.wrapping_mul(&modular_inverse(x)) == one));
     }
-    parametrized_check!(test_inverter);
+    parametrized_check!(small_values);
+
+    quickcheck! {
+        fn random_values_u32(n: u32) -> bool {
+            let n = 2 * n + 1;
+            modular_inverse(n).wrapping_mul(n) == 1
+        }
+
+        fn random_values_u64(n: u64) -> bool {
+            let n = 2 * n + 1;
+            modular_inverse(n).wrapping_mul(n) == 1
+        }
+    }
 }