From f2098548214c1bc617dbb358a5d64ef6d2621fbc Mon Sep 17 00:00:00 2001
From: Diggory Hardy <git@dhardy.name>
Date: Tue, 7 May 2019 16:23:45 +0100
Subject: [PATCH] Fix/update value-stability tests

---
 src/distributions/unit_circle.rs |  6 +++---
 src/distributions/unit_sphere.rs |  6 +++---
 src/lib.rs                       |  6 ++++--
 src/rngs/adapter/reseeding.rs    | 18 ++++++++++--------
 src/rngs/std.rs                  | 18 ++++++++++++++----
 5 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/src/distributions/unit_circle.rs b/src/distributions/unit_circle.rs
index 74a7ea727dc..d078f182d6f 100644
--- a/src/distributions/unit_circle.rs
+++ b/src/distributions/unit_circle.rs
@@ -86,8 +86,8 @@ mod tests {
     fn value_stability() {
         let mut rng = ::test::rng(2);
         let dist = UnitCircle::new();
-        assert_eq!(dist.sample(&mut rng), [-0.8032118336637037, 0.5956935036263119]);
-        assert_eq!(dist.sample(&mut rng), [-0.4742919588505423, -0.880367615130018]);
-        assert_eq!(dist.sample(&mut rng), [0.9297328981467168, 0.368234623716601]);
+        assert_eq!(dist.sample(&mut rng), [0.968253135419177, 0.2499717299034683]);
+        assert_eq!(dist.sample(&mut rng), [-0.2083028196300198, 0.9780643819985387]);
+        assert_eq!(dist.sample(&mut rng), [0.4284767927057159, -0.9035527865667964]);
     }
 }
diff --git a/src/distributions/unit_sphere.rs b/src/distributions/unit_sphere.rs
index af53cdc97b3..4d895ed2359 100644
--- a/src/distributions/unit_sphere.rs
+++ b/src/distributions/unit_sphere.rs
@@ -82,10 +82,10 @@ mod tests {
         let mut rng = ::test::rng(2);
         let dist = UnitSphereSurface::new();
         assert_eq!(dist.sample(&mut rng),
-                   [-0.24950027180862533, -0.7552572587896719, 0.6060825747478084]);
+                   [0.9754391834492048, 0.12388255134190126, -0.18213048307455182]);
         assert_eq!(dist.sample(&mut rng),
-                   [0.47604534507233487, -0.797200864987207, -0.3712837328763685]);
+                   [0.45487349593184284, 0.5619516852114866, -0.6908693119445342]);
         assert_eq!(dist.sample(&mut rng),
-                   [0.9795722330927367, 0.18692349236651176, 0.07414747571708524]);
+                   [-0.8374011645099787, 0.5296803977011814, 0.13489983679919715]);
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index ec2753fda3d..0d398f8d75a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -556,12 +556,14 @@ where Standard: Distribution<T> {
 #[cfg(test)]
 mod test {
     use rngs::mock::StepRng;
-    use rngs::StdRng;
+
     use super::*;
     #[cfg(all(not(feature="std"), feature="alloc"))] use alloc::boxed::Box;
 
     pub fn rng(seed: u64) -> impl RngCore {
-        StdRng::seed_from_u64(seed)
+        // For tests, we want a statistically good, fast, reproducible RNG. We
+        // do not need cryptographic strength. ChaCha8 is a good choice.
+        rand_chacha::ChaCha8Rng::seed_from_u64(seed)
     }
 
     #[test]
diff --git a/src/rngs/adapter/reseeding.rs b/src/rngs/adapter/reseeding.rs
index 2ba35f486ac..29f01e031ad 100644
--- a/src/rngs/adapter/reseeding.rs
+++ b/src/rngs/adapter/reseeding.rs
@@ -340,16 +340,18 @@ mod test {
     fn test_reseeding() {
         let mut zero = StepRng::new(0, 0);
         let rng = ChaCha8Core::from_rng(&mut zero).unwrap();
-        let mut reseeding = ReseedingRng::new(rng, 32*4, zero);
-
-        // Currently we only support for arrays up to length 32.
-        // TODO: cannot generate seq via Rng::gen because it uses different alg
-        let mut buf = [0u32; 32]; // Needs to be a multiple of the RNGs result
-                                  // size to test exactly.
-        reseeding.fill(&mut buf);
+        let thresh = 1; // reseed every time the buffer is exhausted
+        let mut reseeding = ReseedingRng::new(rng, thresh, zero);
+
+        // RNG buffer size is [u32; 64]
+        // Debug is only implemented up to length 32 so use two arrays
+        let mut buf = ([0u32; 32], [0u32; 32]);
+        reseeding.fill(&mut buf.0);
+        reseeding.fill(&mut buf.1);
         let seq = buf;
         for _ in 0..10 {
-            reseeding.fill(&mut buf);
+            reseeding.fill(&mut buf.0);
+            reseeding.fill(&mut buf.1);
             assert_eq!(buf, seq);
         }
     }
diff --git a/src/rngs/std.rs b/src/rngs/std.rs
index 4cdde1d4115..9a6a7ef65c7 100644
--- a/src/rngs/std.rs
+++ b/src/rngs/std.rs
@@ -80,12 +80,22 @@ mod test {
 
     #[test]
     fn test_stdrng_construction() {
+        // Test value-stability of StdRng. This is expected to break any time
+        // the algorithm is changed.
         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                     0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
-        let mut rng1 = StdRng::from_seed(seed);
-        assert_eq!(rng1.next_u64(), 15759097995037006553);
 
-        let mut rng2 = StdRng::from_rng(rng1).unwrap();
-        assert_eq!(rng2.next_u64(), 6766915756997287454);
+        #[cfg(any(feature="stdrng_strong", not(feature="stdrng_fast")))]
+        let target = [3950704604716924505, 5573172343717151650];
+        #[cfg(all(not(feature="stdrng_strong"), feature="stdrng_fast"))]
+        let target = [10719222850664546238, 14064965282130556830];
+        
+        let mut rng0 = StdRng::from_seed(seed);
+        let x0 = rng0.next_u64();
+
+        let mut rng1 = StdRng::from_rng(rng0).unwrap();
+        let x1 = rng1.next_u64();
+
+        assert_eq!([x0, x1], target);
     }
 }