9 张伟 - 第一次作业

Lesson2/README.md

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+## 硅谷live以太坊智能合约频道官方地址
+
+### 第二课《智能合约设计进阶-多员工薪酬系统》
+
+目录结构
+  <br/>|
+  <br/>|--orgin 课程初始代码
+  <br/>|
+  <br/>|--assignment 课程作业提交代码
+<br/> 
+### 本节知识点
+第2课：智能合约设计进阶-多员工薪酬系统
+- 动态静态数组的不同
+- 函数输入参数检查 revert
+- 循环与遍历的安全性
+- 程序运行错误检查和容错：assert与require

Lesson2/assignment/README.md

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+## 硅谷live以太坊智能合约 第二课作业
+这里是同学提交作业的目录
+
+### 第二课：课后作业
+完成今天的智能合约添加100ETH到合约中
+- 加入十个员工，每个员工的薪水都是1ETH
+每次加入一个员工后调用calculateRunway这个函数，并且记录消耗的gas是多少？Gas变化么？如果有 为什么？
+- 如何优化calculateRunway这个函数来减少gas的消耗？
+提交：智能合约代码，gas变化的记录，calculateRunway函数的优化
+

Lesson2/assignment/yours.sol

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+pragma solidity ^0.4.14;
+
+/** @title Payroll contract. */
+contract Payroll {
+    struct Employee {
+        address wallet;
+        uint salary;
+        uint lastPayday;
+    }
+
+    Employee[] employees;
+    address owner;
+    uint constant payDuration = 10 seconds;
+
+    /** @dev Constructor.
+      */
+    function Payroll() {
+        owner = msg.sender;
+    }
+
+    /** @dev Pay employee their rest payment before any change.
+      * @param employee Employee that need to be paid.
+      */
+    function _payRestSalary(Employee employee) private {
+        uint restPayment = employee.salary * (now - employee.lastPayday) / payDuration;
+        employee.wallet.transfer(restPayment);
+    }
+
+    /** @dev Find target employee in employee array.
+      * @param targetWallet Wallet address of the target employee.
+      */
+    function _findEmployee(address targetWallet) private returns (Employee, uint) {
+        for (uint i=0; i<employees.length; i++) {
+            if (employees[i].wallet == targetWallet) {
+                return (employees[i], i);
+            }
+        }
+    }
+
+    /** @dev Add new employee to contract.
+      * @param salary Salary of the new employee.
+      * @param wallet Wallet address of the new employee.
+      */
+    function addEmployee(uint salary, address wallet) {
+        require(msg.sender == owner);
+
+        var (employee,index) = _findEmployee(wallet);
+        assert(employee.wallet == 0x0);
+
+        employees.push(Employee(wallet, salary * 1 ether, now));
+    }
+
+    /** @dev Remove new employee in the contract.
+      * @param salary Salary of the new employee needs to be updated.
+      * @param wallet Wallet address of the employee needs to be updated.
+      */
+    function updateEmployee(uint salary, address wallet) {
+        require(msg.sender == owner);
+        var (employee, index) = _findEmployee(wallet);
+        assert(employee.wallet != 0x0);
+
+        _payRestSalary(employees[index]);
+        employees[index].salary = salary;
+        employees[index].lastPayday = now;
+    }
+
+    /** @dev Update employee in the contract.
+      * @param wallet Wallet address of the employee needs to be removed.
+      */
+    function removeEmployee(address wallet) {
+        require(msg.sender == owner);
+        var (employee, index) = _findEmployee(wallet);
+        assert(employee.wallet != 0x0);
+
+        _payRestSalary(employees[index]);
+        employees[index] = employees[employees.length-1];
+        employees.length-1;
+    }
+
+    /** @dev add fund to employer.
+      * @return employer balance after adding fund.
+      */
+    function addFund() payable returns (uint) {
+        return this.balance;
+    }
+
+    /** @dev calculate how many times the employer can pay the employees
+      * @return the times that employees can get paid from employer's balance
+      */
+    function calculateRunway() returns (uint) {
+        uint totalSalary = 0;
+        for (uint i=0; i<employees.length; i++) {
+            totalSalary += employees[i].salary;
+        }
+        return this.balance / totalSalary;
+    }
+
+    /** @dev check if employer has enough money to pay
+      * @return true means employers has enough money, false means not
+      */
+    function hasEnoughFund() returns (bool) {
+        return calculateRunway() > 0;
+    }
+
+    /** @dev pay salary to employee
+      */
+    function getPaid() {
+        var (employee, index) = _findEmployee(msg.sender);
+        assert(employee.wallet == 0x0);
+
+        uint nextPayDay = employee.lastPayday + payDuration;
+        if (nextPayDay > now) {
+            revert();
+        } 
+
+        employees[index].lastPayday = nextPayDay;
+        employees[index].wallet.transfer(employee.salary);
+    }
+}
+
+//gas history
+0xca35b7d915458ef540ade6068dfe2f44e8fa733c
+transaction cost  23009 gas 
+execution cost   1737 gas 
+
+0x14723a09acff6d2a60dcdf7aa4aff308fddc160c
+transaction cost  23779 gas 
+execution cost   2507 gas
+
+0x583031d1113ad414f02576bd6afabfb302140225
+transaction cost  24549 gas 
+execution cost   3277 gas
+
+0xdd870fa1b7c4700f2bd7f44238821c26f7392148
+transaction cost  25319 gas 
+execution cost   4047 gas
+
+//transaction cost 和 execution cost都在逐渐提升
+
+//原因：我认为是因为Employee数组中的员工数量递增，使得for循环次数增加，导致计算成本加大，从而gas cost升高。
+
+//优化：不必每次调用calculateRunway都调用for循环来计算totalSalary，可以在每次添加新员工是进行计算，还要在更新员工信息的时候进行更新。
+//优化代码
+pragma solidity ^0.4.14;
+
+/** @title Payroll contract. */
+contract Payroll {
+    struct Employee {
+        address wallet;
+        uint salary;
+        uint lastPayday;
+    }
+
+    Employee[] employees;
+    address owner;
+    uint totalSalary = 0;
+    uint constant payDuration = 10 seconds;
+
+    /** @dev Constructor.
+      */
+    function Payroll() {
+        owner = msg.sender;
+    }
+
+    /** @dev Pay employee their rest payment before any change.
+      * @param employee Employee that need to be paid.
+      */
+    function _payRestSalary(Employee employee) private {
+        uint restPayment = employee.salary * (now - employee.lastPayday) / payDuration;
+        employee.wallet.transfer(restPayment);
+    }
+
+    /** @dev Find target employee in employee array.
+      * @param targetWallet Wallet address of the target employee.
+      */
+    function _findEmployee(address targetWallet) private returns (Employee, uint) {
+        for (uint i=0; i<employees.length; i++) {
+            if (employees[i].wallet == targetWallet) {
+                return (employees[i], i);
+            }
+        }
+    }
+
+    /** @dev Add new employee to contract.
+      * @param salary Salary of the new employee.
+      * @param wallet Wallet address of the new employee.
+      */
+    function addEmployee(uint salary, address wallet) {
+        require(msg.sender == owner);
+
+        var (employee,index) = _findEmployee(wallet);
+        assert(employee.wallet == 0x0);
+
+        employees.push(Employee(wallet, salary * 1 ether, now));
+        totalSalary += salary * 1 ether;
+    }
+
+    /** @dev Remove new employee in the contract.
+      * @param salary Salary of the new employee needs to be updated.
+      * @param wallet Wallet address of the employee needs to be updated.
+      */
+    function updateEmployee(uint salary, address wallet) {
+        require(msg.sender == owner);
+        var (employee, index) = _findEmployee(wallet);
+        assert(employee.wallet != 0x0);
+
+        _payRestSalary(employees[index]);
+        totalSalary = totalSalary - employees[index].salary;
+        employees[index].salary = salary * 1 ether;
+        totalSalary = totalSalary + salary;
+
+        employees[index].lastPayday = now;
+    }
+
+    /** @dev Update employee in the contract.
+      * @param wallet Wallet address of the employee needs to be removed.
+      */
+    function removeEmployee(address wallet) {
+        require(msg.sender == owner);
+        var (employee, index) = _findEmployee(wallet);
+        assert(employee.wallet != 0x0);
+
+        _payRestSalary(employees[index]);
+        employees[index] = employees[employees.length-1];
+        employees.length-1;
+    }
+
+    /** @dev add fund to employer.
+      * @return employer balance after adding fund.
+      */
+    function addFund() payable returns (uint) {
+        return this.balance;
+    }
+
+    /** @dev calculate how many times the employer can pay the employees
+      * @return the times that employees can get paid from employer's balance
+      */
+    function calculateRunway() returns (uint) {
+        return this.balance / totalSalary;
+    }
+
+    /** @dev check if employer has enough money to pay
+      * @return true means employers has enough money, false means not
+      */
+    function hasEnoughFund() returns (bool) {
+        return calculateRunway() > 0;
+    }
+
+    /** @dev pay salary to employee
+      */
+    function getPaid() {
+        var (employee, index) = _findEmployee(msg.sender);
+        assert(employee.wallet == 0x0);
+
+        uint nextPayDay = employee.lastPayday + payDuration;
+        if (nextPayDay > now) {
+            revert();
+        } 
+
+        employees[index].lastPayday = nextPayDay;
+        employees[index].wallet.transfer(employee.salary);
+    }
+}
+
+//new gas history
+0xca35b7d915458ef540ade6068dfe2f44e8fa733c
+transaction cost  125490 gas 
+execution cost   102618 gas
+
+0x14723a09acff6d2a60dcdf7aa4aff308fddc160c
+transaction cost  22202 gas 
+execution cost   930 gas
+
+0x4b0897b0513fdc7c541b6d9d7e929c4e5364d2db
+transaction cost  22202 gas 
+execution cost   930 gas
+
+0x583031d1113ad414f02576bd6afabfb302140225
+transaction cost   22202 gas 
+execution cost   930 gas
+
+//gas 不变了，因为calculateRunway现在只是做一个除法

Lesson2/orgin/README.md

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+## 硅谷live以太坊智能合约 第二课《智能合约设计进阶-多员工薪酬系统》
+
+这里是每一课的初始代码，有需要的同学可以参考

Lesson2/orgin/payroll.sol

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+pragma solidity ^0.4.14;
+
+contract Payroll {
+    struct Employee {
+        address id;
+        uint salary;
+        uint lastPayday;
+    }
+
+    uint constant payDuration = 10 seconds;
+
+    address owner;
+    Employee[] employees;
+
+    function Payroll() {
+        owner = msg.sender;
+    }
+
+    function _partialPaid(Employee employee) private {
+    }
+
+    function _findEmployee(address employeeId) private returns (Employee, uint) {
+    }
+
+    function addEmployee(address employeeId, uint salary) {
+    }
+
+    function removeEmployee(address employeeId) {
+    }
+
+    function updateEmployee(address employeeId, uint salary) {
+    }
+
+    function addFund() payable returns (uint) {
+    }
+
+    function calculateRunway() returns (uint) {
+        uint totalSalary = 0;
+       for (uint i = 0; i < employees.length; i++) {
+            totalSalary += employees[i].salary;
+        }
+        return this.balance / totalSalary;
+    }
+
+    function hasEnoughFund() returns (bool) {
+    }
+
+    function getPaid() {
+    }
+}