From 44fe85b52892ca00bd482c76282426fbf830b998 Mon Sep 17 00:00:00 2001
From: Xavier Leroy <xavier.leroy@inria.fr>
Date: Mon, 14 May 2018 09:46:42 +0200
Subject: [PATCH] In Splitmix.mixGamma, wrong test for weak Gamma values (#2)

The "popcount >= 24" test was taken from the original Splitmix paper,
but is wrong: it should be  "popcount < 24", as explained in the paper
and here http://www.pcg-random.org/posts/bugs-in-splitmix.html

Closes: #2
---
 Changes | 1 +
 stubs.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
 create mode 100644 Changes

diff --git a/Changes b/Changes
new file mode 100644
index 0000000..e73a198
--- /dev/null
+++ b/Changes
@@ -0,0 +1 @@
+- #2: in Splitmix.mixGamma, wrong test for weak Gamma values
diff --git a/stubs.c b/stubs.c
index af75b84..fd8de32 100644
--- a/stubs.c
+++ b/stubs.c
@@ -74,7 +74,7 @@ static inline int popcount64(uint64_t x)
 CAMLprim uint64_t pringo_mixGamma_unboxed(uint64_t z)
 {
   z = mix64variant13(z) | 1ULL;
-  if (popcount64(z ^ (z >> 1)) >= 24) z ^= 0xaaaaaaaaaaaaaaaaULL;
+  if (popcount64(z ^ (z >> 1)) < 24) z ^= 0xaaaaaaaaaaaaaaaaULL;
   return z; 
 }