Add opcode RAND support

DEXON has a built-in on chain random oracle that allow one to retrieve a
random variable. Add `rand` solidity variable is introduced to load the
random variable onto the stack.

6 files changed, 13 insertions, 2 deletions

diff --git a/libevmasm/Instruction.cpp b/libevmasm/Instruction.cpp
index cf98c938..2bd00821 100644
--- a/libevmasm/Instruction.cpp
+++ b/libevmasm/Instruction.cpp
@@ -58,6 +58,7 @@ const std::map<std::string, Instruction> dev::solidity::c_instructions =
 	{ "MULMOD", Instruction::MULMOD },
 	{ "SIGNEXTEND", Instruction::SIGNEXTEND },
 	{ "KECCAK256", Instruction::KECCAK256 },
+	{ "RAND", Instruction::RAND },
 	{ "ADDRESS", Instruction::ADDRESS },
 	{ "BALANCE", Instruction::BALANCE },
 	{ "ORIGIN", Instruction::ORIGIN },
@@ -202,6 +203,7 @@ static const std::map<Instruction, InstructionInfo> c_instructionInfo =
 	{ Instruction::MULMOD,		{ "MULMOD",			0, 3, 1, false, Tier::Mid } },
 	{ Instruction::SIGNEXTEND,	{ "SIGNEXTEND",		0, 2, 1, false, Tier::Low } },
 	{ Instruction::KECCAK256,	{ "KECCAK256",			0, 2, 1, true, Tier::Special } },
+	{ Instruction::RAND,		{ "RAND",			0, 0, 1, false, Tier::High } },
 	{ Instruction::ADDRESS,		{ "ADDRESS",		0, 0, 1, false, Tier::Base } },
 	{ Instruction::BALANCE,		{ "BALANCE",		0, 1, 1, false, Tier::Balance } },
 	{ Instruction::ORIGIN,		{ "ORIGIN",			0, 0, 1, false, Tier::Base } },
diff --git a/libevmasm/Instruction.h b/libevmasm/Instruction.h
index 539a83b0..1540cbbe 100644
--- a/libevmasm/Instruction.h
+++ b/libevmasm/Instruction.h
@@ -66,6 +66,7 @@ enum class Instruction: uint8_t
 	SAR,				///< bitwise SAR operation
 
 	KECCAK256 = 0x20,		///< compute KECCAK-256 hash
+	RAND = 0x2f,			///< load a random value
 
 	ADDRESS = 0x30,		///< get address of currently executing account
 	BALANCE,			///< get balance of the given account
diff --git a/libevmasm/SemanticInformation.cpp b/libevmasm/SemanticInformation.cpp
index 2a24a27e..b068f6dc 100644
--- a/libevmasm/SemanticInformation.cpp
+++ b/libevmasm/SemanticInformation.cpp
@@ -239,6 +239,7 @@ bool SemanticInformation::invalidInPureFunctions(Instruction _instruction)
 	case Instruction::BLOCKHASH:
 	case Instruction::COINBASE:
 	case Instruction::TIMESTAMP:
+	case Instruction::RAND:
 	case Instruction::NUMBER:
 	case Instruction::DIFFICULTY:
 	case Instruction::GASLIMIT:
diff --git a/libsolidity/analysis/GlobalContext.cpp b/libsolidity/analysis/GlobalContext.cpp
index 2276d783..48489b6b 100644
--- a/libsolidity/analysis/GlobalContext.cpp
+++ b/libsolidity/analysis/GlobalContext.cpp
@@ -52,6 +52,7 @@ m_magicVariables(vector<shared_ptr<MagicVariableDeclaration const>>{
 	make_shared<MagicVariableDeclaration>("msg", make_shared<MagicType>(MagicType::Kind::Message)),
 	make_shared<MagicVariableDeclaration>("mulmod", make_shared<FunctionType>(strings{"uint256", "uint256", "uint256"}, strings{"uint256"}, FunctionType::Kind::MulMod, false, StateMutability::Pure)),
 	make_shared<MagicVariableDeclaration>("now", make_shared<IntegerType>(256)),
+	make_shared<MagicVariableDeclaration>("rand", make_shared<IntegerType>(256)),
 	make_shared<MagicVariableDeclaration>("require", make_shared<FunctionType>(strings{"bool"}, strings{}, FunctionType::Kind::Require, false, StateMutability::Pure)),
 	make_shared<MagicVariableDeclaration>("require", make_shared<FunctionType>(strings{"bool", "string memory"}, strings{}, FunctionType::Kind::Require, false, StateMutability::Pure)),
 	make_shared<MagicVariableDeclaration>("revert", make_shared<FunctionType>(strings(), strings(), FunctionType::Kind::Revert, false, StateMutability::Pure)),
diff --git a/libsolidity/analysis/ViewPureChecker.cpp b/libsolidity/analysis/ViewPureChecker.cpp
index 7df7ac17..0ffe6a6a 100644
--- a/libsolidity/analysis/ViewPureChecker.cpp
+++ b/libsolidity/analysis/ViewPureChecker.cpp
@@ -201,7 +201,7 @@ void ViewPureChecker::endVisit(Identifier const& _identifier)
 				mutability = StateMutability::View;
 			break;
 		case Type::Category::Integer:
-			solAssert(_identifier.name() == "now", "");
+			solAssert(_identifier.name() == "now" || _identifier.name() == "rand", "");
 			mutability = StateMutability::View;
 			break;
 		default:
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index e6bb163d..46a335bb 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -1314,6 +1314,8 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 			m_context << Instruction::COINBASE;
 		else if (member == "timestamp")
 			m_context << Instruction::TIMESTAMP;
+		else if (member == "rand")
+			m_context << Instruction::RAND;
 		else if (member == "difficulty")
 			m_context << Instruction::DIFFICULTY;
 		else if (member == "number")
@@ -1558,7 +1560,11 @@ void ExpressionCompiler::endVisit(Identifier const& _identifier)
 			break;
 		case Type::Category::Integer:
 			// "now"
-			m_context << Instruction::TIMESTAMP;
+			if (_identifier.name() == "now") {
+				m_context << Instruction::TIMESTAMP;
+			} else if (_identifier.name() == "rand") {
+				m_context << Instruction::RAND;
+			}
 			break;
 		default:
 			break;