From 354468ed6a07ddbf0d74cddca3d3805c9a99c6d7 Mon Sep 17 00:00:00 2001
From: Diggory Hardy <git@dhardy.name>
Date: Sun, 13 Dec 2020 14:16:18 +0000
Subject: [PATCH] Use approximate assertions in value stability and increase
 some tolerences slightly

---
 rand_distr/src/cauchy.rs            |  2 +-
 rand_distr/src/normal.rs            |  3 +-
 rand_distr/src/pareto.rs            | 16 +++++------
 rand_distr/tests/value_stability.rs | 44 +++++++++++++++++++++++++----
 4 files changed, 50 insertions(+), 15 deletions(-)

diff --git a/rand_distr/src/cauchy.rs b/rand_distr/src/cauchy.rs
index ffe86d00a9b..1fadf0c6f61 100644
--- a/rand_distr/src/cauchy.rs
+++ b/rand_distr/src/cauchy.rs
@@ -160,7 +160,7 @@ mod test {
         let expected = [15.023088, -5.446413, 3.7092876, 3.112482];
         for (a, b) in buf.iter().zip(expected.iter()) {
             let (a, b) = (*a, *b);
-            assert!((a - b).abs() < 1e-6, "expected: {} = {}", a, b);
+            assert!((a - b).abs() < 1e-5, "expected: {} = {}", a, b);
         }
     }
 }
diff --git a/rand_distr/src/normal.rs b/rand_distr/src/normal.rs
index ae82799147a..4ab0fbd1901 100644
--- a/rand_distr/src/normal.rs
+++ b/rand_distr/src/normal.rs
@@ -345,7 +345,8 @@ mod tests {
         assert_almost_eq!(lnorm.norm.std_dev, 1.0, 2e-16);
 
         let lnorm = LogNormal::from_mean_cv(e.powf(1.5), (e - 1.0).sqrt()).unwrap();
-        assert_eq!((lnorm.norm.mean, lnorm.norm.std_dev), (1.0, 1.0));
+        assert!((lnorm.norm.mean - 1.0).abs() < 1e-15);
+        assert_eq!(lnorm.norm.std_dev, 1.0);
     }
     #[test]
     fn test_log_normal_invalid_sd() {
diff --git a/rand_distr/src/pareto.rs b/rand_distr/src/pareto.rs
index 217899ed9a7..0c62383b1cb 100644
--- a/rand_distr/src/pareto.rs
+++ b/rand_distr/src/pareto.rs
@@ -87,6 +87,7 @@ where F: Float, OpenClosed01: Distribution<F>
 #[cfg(test)]
 mod tests {
     use super::*;
+    use core::fmt::{Debug, Display};
 
     #[test]
     #[should_panic]
@@ -108,21 +109,20 @@ mod tests {
 
     #[test]
     fn value_stability() {
-        fn test_samples<F: Float + core::fmt::Debug, D: Distribution<F>>(
-            distr: D, zero: F, expected: &[F],
+        fn test_samples<F: Float + Debug + Display, D: Distribution<F>>(
+            distr: D, thresh: F, expected: &[F],
         ) {
             let mut rng = crate::test::rng(213);
-            let mut buf = [zero; 4];
-            for x in &mut buf {
-                *x = rng.sample(&distr);
+            for v in expected {
+                let x = rng.sample(&distr);
+                assert!((x - *v).abs() < thresh, "not approx eq: {}, {}", x, *v);
             }
-            assert_eq!(buf, expected);
         }
 
-        test_samples(Pareto::new(1.0, 1.0).unwrap(), 0f32, &[
+        test_samples(Pareto::new(1f32, 1.0).unwrap(), 1e-6, &[
             1.0423688, 2.1235929, 4.132709, 1.4679428,
         ]);
-        test_samples(Pareto::new(2.0, 0.5).unwrap(), 0f64, &[
+        test_samples(Pareto::new(2.0, 0.5).unwrap(), 1e-14, &[
             9.019295276219136,
             4.3097126018270595,
             6.837815045397157,
diff --git a/rand_distr/tests/value_stability.rs b/rand_distr/tests/value_stability.rs
index 986b9963283..aafb95552d5 100644
--- a/rand_distr/tests/value_stability.rs
+++ b/rand_distr/tests/value_stability.rs
@@ -6,7 +6,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::{fmt::Debug, cmp::PartialEq};
+use core::fmt::Debug;
 use rand::Rng;
 use rand_distr::*;
 
@@ -17,12 +17,45 @@ fn get_rng(seed: u64) -> impl rand::Rng {
     rand_pcg::Pcg32::new(seed, INC)
 }
 
-fn test_samples<F: Debug + Copy + PartialEq, D: Distribution<F>>(
+/// We only assert approximate equality since some platforms do not perform
+/// identically (i686-unknown-linux-gnu and most notably x86_64-pc-windows-gnu).
+trait ApproxEq {
+    fn is_approx_eq(&self, rhs: &Self) -> bool;
+}
+
+impl ApproxEq for f32 {
+    fn is_approx_eq(&self, rhs: &Self) -> bool {
+        (self - rhs).abs() < 1e-6
+    }
+}
+impl ApproxEq for f64 {
+    fn is_approx_eq(&self, rhs: &Self) -> bool {
+        (self - rhs).abs() < 1e-14
+    }
+}
+impl ApproxEq for u64 {
+    fn is_approx_eq(&self, rhs: &Self) -> bool {
+        self == rhs
+    }
+}
+impl<T: ApproxEq> ApproxEq for [T; 2] {
+    fn is_approx_eq(&self, rhs: &Self) -> bool {
+        self[0].is_approx_eq(&rhs[0]) && self[1].is_approx_eq(&rhs[1])
+    }
+}
+impl<T: ApproxEq> ApproxEq for [T; 3] {
+    fn is_approx_eq(&self, rhs: &Self) -> bool {
+        self[0].is_approx_eq(&rhs[0]) && self[1].is_approx_eq(&rhs[1]) && self[2].is_approx_eq(&rhs[2])
+    }
+}
+
+fn test_samples<F: Debug + ApproxEq, D: Distribution<F>>(
     seed: u64, distr: D, expected: &[F],
 ) {
     let mut rng = get_rng(seed);
-    for &val in expected {
-        assert_eq!(val, rng.sample(&distr));
+    for val in expected {
+        let x = rng.sample(&distr);
+        assert!(x.is_approx_eq(&val), "not approx eq: {:?}, {:?}", x, val);
     }
 }
 
@@ -334,11 +367,12 @@ fn cauchy_stability() {
 
     // Unfortunately this test is not fully portable due to reliance on the
     // system's implementation of tanf (see doc on Cauchy struct).
+    // We use a lower threshold of 1e-5 here.
     let distr = Cauchy::new(10f32, 7.0).unwrap();
     let mut rng = get_rng(353);
     let expected = [15.023088, -5.446413, 3.7092876, 3.112482];
     for &a in expected.iter() {
         let b = rng.sample(&distr);
-        assert!((a - b).abs() < 1e-6, "expected: {} = {}", a, b);
+        assert!((a - b).abs() < 1e-5, "not approx eq: {:?}, {:?}", a, b);
     }
 }