Variable EXP gas cost.

libevm/FeeStructure.cpp

@@ -34,6 +34,8 @@ u256 const dev::eth::c_sstoreResetGas = 100;
 u256 const dev::eth::c_sstoreRefundGas = 100;
 u256 const dev::eth::c_createGas = 100;
 u256 const dev::eth::c_callGas = 20;
+u256 const dev::eth::c_expGas = 1;
+u256 const dev::eth::c_expByteGas = 1;
 u256 const dev::eth::c_memoryGas = 1;
 u256 const dev::eth::c_txDataZeroGas = 1;
 u256 const dev::eth::c_txDataNonZeroGas = 5;

libevm/FeeStructure.h

@@ -37,6 +37,8 @@ extern u256 const c_sstoreResetGas;		///< Once per SSTORE operation if the zeron
 extern u256 const c_sstoreRefundGas;	///< Refunded gas, once per SSTORE operation if the zeroness changes to zero.
 extern u256 const c_createGas;			///< Once per CREATE operation & contract-creation transaction.
 extern u256 const c_callGas;			///< Once per CALL operation & message call transaction.
+extern u256 const c_expGas;				///< Once per EXP instuction.
+extern u256 const c_expByteGas;			///< Times ceil(log256(exponent)) for the EXP instruction.
 extern u256 const c_memoryGas;			///< Times the address of the (highest referenced byte in memory + 1). NOTE: referencing happens on read, write and in instructions such as RETURN and CALL.
 extern u256 const c_txDataZeroGas;		///< Per byte of data attached to a transaction that equals zero. NOTE: Not payable on data of calls between transactions.
 extern u256 const c_txDataNonZeroGas;	///< Per byte of data attached to a transaction that is not equal to zero. NOTE: Not payable on data of calls between transactions.

libevm/VM.h

@@ -242,6 +242,13 @@ template <class Ext> dev::bytesConstRef dev::eth::VM::go(Ext& _ext, OnOpFunc con
             runGas = c_createGas;
 			break;
 		}
+		case Instruction::EXP:
+		{
+			require(2);
+			auto expon = m_stack[m_stack.size() - 2];
+			runGas = c_expGas + c_extByteGas * (32 - (h256(expon).firstBitSet() / 8));
+			break;
+		}
 
 		case Instruction::PC:
 		case Instruction::MSIZE:
@@ -308,7 +315,6 @@ template <class Ext> dev::bytesConstRef dev::eth::VM::go(Ext& _ext, OnOpFunc con
 		case Instruction::SDIV:
 		case Instruction::MOD:
 		case Instruction::SMOD:
-		case Instruction::EXP:
 		case Instruction::LT:
 		case Instruction::GT:
 		case Instruction::SLT: