https://git.ruby-lang.org/ruby.git/commit/?id=eb21e8add3

From eb21e8add346854aa93299bf767f119439f74f7a Mon Sep 17 00:00:00 2001
From: Yusuke Endoh <mame@r...>
Date: Mon, 12 Oct 2020 13:45:32 +0900
Subject: bignum.c (bary_sparse_p): do not comsume Random::DEFAULT

It uses random to determine if the bignum is sparse or not.
It is arguable if three-digit samples are enough or not to determine it,
but anyway, consuming Random source implicitly is not good.

I introduced the random sampling mechanism, and I don't know any
significant reason to do so.  So, let's remove it.
This change makes the sampling points fixed: 40th, 50th, and 60th
percentiles.

diff --git a/bignum.c b/bignum.c
index cd969ac..0515e2f 100644
--- a/bignum.c
+++ b/bignum.c
@@ -2359,9 +2359,9 @@ bary_sparse_p(const BDIGIT *ds, size_t n) https://github.com/ruby/ruby/blob/trunk/bignum.c#L2359
 {
     long c = 0;
 
-    if (          ds[rb_genrand_ulong_limited(n / 2) + n / 4]) c++;
-    if (c <= 1 && ds[rb_genrand_ulong_limited(n / 2) + n / 4]) c++;
-    if (c <= 1 && ds[rb_genrand_ulong_limited(n / 2) + n / 4]) c++;
+    if (          ds[2 * n / 5]) c++;
+    if (c <= 1 && ds[    n / 2]) c++;
+    if (c <= 1 && ds[3 * n / 5]) c++;
 
     return (c <= 1) ? 1 : 0;
 }
-- 
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