From 3f8d5ebedf387495ece37dfe50288884768f6dfb Mon Sep 17 00:00:00 2001
From: Cuda-Chen <clh960524@gmail.com>
Date: Tue, 25 Jul 2023 16:08:09 +0800
Subject: [PATCH] Use SplitMix64 for seeding test cases

Close #581.
---
 tests/impl.cpp | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/tests/impl.cpp b/tests/impl.cpp
index 82b58b3c..cd16a2af 100644
--- a/tests/impl.cpp
+++ b/tests/impl.cpp
@@ -350,10 +350,21 @@ static inline double bankersRounding(double val)
     return ret;
 }
 
-static float ranf(void)
+// by Sebastiano Vigna, see: <https://xoshiro.di.unimi.it/splitmix64.c>
+static uint64_t x;
+const double TWOPOWER64 = pow(2, 64);
+
+static double next()
+{
+    uint64_t z = (x += 0x9e3779b97f4a7c15);
+    z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
+    z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
+    return z ^ (z >> 31);
+}
+
+static float ranf()
 {
-    uint32_t ir = rand() & 0x7FFF;
-    return (float) ir * (1.0f / 32768.0f);
+    return next() / TWOPOWER64;
 }
 
 static float ranf(float low, float high)