From f73af1a67d5299c048782cd281e99f02ef471081 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 12 Jun 2023 15:12:33 +0200
Subject: [PATCH] Fix negative shift value UB

---
 include/boost/charconv/detail/emulated128.hpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/boost/charconv/detail/emulated128.hpp b/include/boost/charconv/detail/emulated128.hpp
index 8d9fc53..2c461de 100644
--- a/include/boost/charconv/detail/emulated128.hpp
+++ b/include/boost/charconv/detail/emulated128.hpp
@@ -722,7 +722,11 @@ BOOST_CHARCONV_CXX14_CONSTEXPR void div_impl(uint128 lhs, uint128 rhs, uint128&
     uint128 denom = rhs;
     quotient = 0U;
 
-    const int shift = high_bit(lhs) - high_bit(rhs);
+    std::int32_t shift = high_bit(lhs) - high_bit(rhs);
+    if (shift < 0)
+    {
+        shift = 32 - shift;
+    }
     denom <<= shift;
 
     for (int i = 0; i <= shift; ++i)