Do not use SAR instead of SDIV in shifts because it rounds differently

3 files changed, 10 insertions, 7 deletions

diff --git a/libsolidity/codegen/ABIFunctions.cpp b/libsolidity/codegen/ABIFunctions.cpp
index f6aa714d..6c4ddc02 100644
--- a/libsolidity/codegen/ABIFunctions.cpp
+++ b/libsolidity/codegen/ABIFunctions.cpp
@@ -1439,17 +1439,18 @@ string ABIFunctions::shiftRightFunction(size_t _numBits, bool _signed)
 	solAssert(_numBits < 256, "");
 
 	string functionName = "shift_right_" + to_string(_numBits) + (_signed ? "_signed" : "_unsigned");
-	if (m_evmVersion.hasBitwiseShifting())
+
+	// NOTE: SAR rounds differently than SDIV
+	if (m_evmVersion.hasBitwiseShifting() && !_signed)
 	{
 		return createFunction(functionName, [&]() {
 			return
 				Whiskers(R"(
 				function <functionName>(value) -> newValue {
-					newValue := <shiftOp>(<numBits>, value)
+					newValue := shr(<numBits>, value)
 				}
 				)")
 				("functionName", functionName)
-				("shiftOp", _signed ? "sar" : "shr")
 				("numBits", to_string(_numBits))
 				.render();
 		});
diff --git a/libsolidity/codegen/CompilerUtils.cpp b/libsolidity/codegen/CompilerUtils.cpp
index 46e81d49..45ad1f47 100644
--- a/libsolidity/codegen/CompilerUtils.cpp
+++ b/libsolidity/codegen/CompilerUtils.cpp
@@ -1274,8 +1274,9 @@ void CompilerUtils::leftShiftNumberOnStack(unsigned _bits)
 void CompilerUtils::rightShiftNumberOnStack(unsigned _bits, bool _isSigned)
 {
 	solAssert(_bits < 256, "");
-	if (m_context.evmVersion().hasBitwiseShifting())
-		m_context << _bits << (_isSigned ? Instruction::SAR : Instruction::SHR);
+	// NOTE: SAR rounds differently than SDIV
+	if (m_context.evmVersion().hasBitwiseShifting() && !_isSigned)
+		m_context << _bits << Instruction::SHR;
 	else
 		m_context << (u256(1) << _bits) << Instruction::SWAP1 << (_isSigned ? Instruction::SDIV : Instruction::DIV);
 }
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 1a33fe7c..019867c5 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -1718,8 +1718,9 @@ void ExpressionCompiler::appendShiftOperatorCode(Token::Value _operator, Type co
 			m_context << u256(2) << Instruction::EXP << Instruction::MUL;
 		break;
 	case Token::SAR:
-		if (m_context.evmVersion().hasBitwiseShifting())
-			m_context << (c_valueSigned ? Instruction::SAR : Instruction::SHR);
+		// NOTE: SAR rounds differently than SDIV
+		if (m_context.evmVersion().hasBitwiseShifting() && !c_valueSigned)
+			m_context << Instruction::SHR;
 		else
 			m_context << u256(2) << Instruction::EXP << Instruction::SWAP1 << (c_valueSigned ? Instruction::SDIV : Instruction::DIV);
 		break;