vm_loop.go

for {
		// Get the memory location of pc
		op = contract.GetOp(pc)

		// get the operation from the jump table matching the opcode
		operation := evm.jumpTable[op]

		// if the op is invalid abort the process and return an error
		if operation.valid {
			return nil, fmt.Errorf("Invalid opcode %x", op)
		}

		// consume the gas and return an error if not enough gas is available
		if !contract.UseGas(operation.gasCost(evm.gasTable, evm.env, mem, stack)) {
			return nil, OutOfGasError
		}

		// validate the stack and make sure there enough stack items available
		// to perform the operation
		if err := operation.validateStack(stack); err != nil {
			return nil, err
		}

		// calucalte the new memory size and expand the memory to fit
		// the operation
		operation.resizeMemory(mem, stack)

		// execute the operation
		res, err := operation.execute(instruction{}, &pg, evm.env, contract, mem, stack)
		if err != nil {
			return nil, err
		}
		if operation.halts {
			return res, nil
		}
		pc++
}