From e7084d9e16d0b370cab29d1f9ba08f07844b55f5 Mon Sep 17 00:00:00 2001
From: chriseth <c@ethdev.com>
Date: Fri, 12 Aug 2016 16:50:37 +0200
Subject: [PATCH] Throw on division by zero.

---
 docs/types.rst                             |  2 ++
 libsolidity/codegen/ExpressionCompiler.cpp | 13 ++++++++++---
 test/libsolidity/SolidityEndToEndTest.cpp  | 21 +++++++++++++++++++++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/docs/types.rst b/docs/types.rst
index 31f6b53d8..d6445ed98 100644
--- a/docs/types.rst
+++ b/docs/types.rst
@@ -57,6 +57,8 @@ Operators:
 Division always truncates (it just maps to the DIV opcode of the EVM), but it does not truncate if both
 operators are :ref:`literals<rational_literals>` (or literal expressions).
 
+Division by zero and modulus with zero throws an exception.
+
 .. index:: address, balance, send, call, callcode, delegatecall
 
 .. _address:
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 1f93cf8cb..4695ff964 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -1324,11 +1324,18 @@ void ExpressionCompiler::appendArithmeticOperatorCode(Token::Value _operator, Ty
 		m_context << Instruction::MUL;
 		break;
 	case Token::Div:
-		m_context  << (c_isSigned ? Instruction::SDIV : Instruction::DIV);
-		break;
 	case Token::Mod:
-		m_context << (c_isSigned ? Instruction::SMOD : Instruction::MOD);
+	{
+		// Test for division by zero
+		m_context << Instruction::DUP2 << Instruction::ISZERO;
+		m_context.appendConditionalJumpTo(m_context.errorTag());
+
+		if (_operator == Token::Div)
+			m_context << (c_isSigned ? Instruction::SDIV : Instruction::DIV);
+		else
+			m_context << (c_isSigned ? Instruction::SMOD : Instruction::MOD);
 		break;
+	}
 	case Token::Exp:
 		m_context << Instruction::EXP;
 		break;
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index 3920d9482..647199ea7 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -6208,6 +6208,27 @@ BOOST_AUTO_TEST_CASE(addmod_mulmod)
 	BOOST_CHECK(callContractFunction("test()") == encodeArgs(u256(0)));
 }
 
+BOOST_AUTO_TEST_CASE(divisiod_by_zero)
+{
+	char const* sourceCode = R"(
+		contract C {
+			function div(uint a, uint b) returns (uint) {
+				return a / b;
+			}
+			function mod(uint a, uint b) returns (uint) {
+				return a % b;
+			}
+		}
+	)";
+	compileAndRun(sourceCode);
+	BOOST_CHECK(callContractFunction("div(uint256,uint256)", 7, 2) == encodeArgs(u256(3)));
+	// throws
+	BOOST_CHECK(callContractFunction("div(uint256,uint256)", 7, 0) == encodeArgs());
+	BOOST_CHECK(callContractFunction("mod(uint256,uint256)", 7, 2) == encodeArgs(u256(1)));
+	// throws
+	BOOST_CHECK(callContractFunction("mod(uint256,uint256)", 7, 0) == encodeArgs());
+}
+
 BOOST_AUTO_TEST_CASE(string_allocation_bug)
 {
 	char const* sourceCode = R"(