From 5df3f8221d48f2007efb9611fed873bac64cacd6 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Fri, 29 Jul 2022 10:14:05 +0900
Subject: [PATCH] bigint.c (lzb): check `x==0` before calling clz().

In theory, we should not call lzb() with 0, and we assume checks are
done before calling it. But we got a report that we call lzb(0) in some
use-case. We could not reproduce the issue, so we add this guard.
---
 mrbgems/mruby-bigint/core/bigint.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index b7ad5d14f..90fa08417 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -350,6 +350,7 @@ mpz_mul_int(mrb_state *mrb, mpz_t *x, mpz_t *y, mrb_int n)
 static int
 lzb(mp_limb x)
 {
+  if (x == 0) return 0;
 #if (defined(__GNUC__) || __has_builtin(__builtin_clz))
   if (sizeof(mp_limb) == sizeof(int64_t))
     return __builtin_clzll(x);