Use proper SAR for signed right shifts and emulate on pre-constantinople.

1 files changed, 9 insertions, 2 deletions

diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index 1e0565c0..94e04b6a 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -1084,9 +1084,16 @@ TypePointer RationalNumberType::binaryOperatorResult(Token::Value _operator, Typ
 			{
 				uint32_t exponent = other.m_value.numerator().convert_to<uint32_t>();
 				if (exponent > mostSignificantBit(boost::multiprecision::abs(m_value.numerator())))
-					value = 0;
+					value = m_value.numerator() < 0 ? -1 : 0;
 				else
-					value = rational(m_value.numerator() / boost::multiprecision::pow(bigint(2), exponent), 1);
+				{
+					if (m_value.numerator() < 0)
+						// add 1 to the negative value before dividing to get a result that is strictly too large
+						// subtract 1 afterwards to round towards negative infinity
+						value = rational((m_value.numerator() + 1) / boost::multiprecision::pow(bigint(2), exponent) - bigint(1), 1);
+					else
+						value = rational(m_value.numerator() / boost::multiprecision::pow(bigint(2), exponent), 1);
+				}
 			}
 			break;
 		}