Openzeppelin学习记录二:utils模块(SafeMath.sol+SafeCast.sol)
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2.Utils
这个模块下有很多solidity并没有提供,但很好用的合约,比如超级典中典safemath库。接下来先介绍一下比较常用的几个库合约
2.1 Math
本库合约提供了最大最小值,平均值,整除向上取整等常用操作。
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
//提供了最大最小值,平均值,整除向上取整等常用操作。
/**
* @dev Standard math utilities missing in the Solidity language.
*/
library Math {
/**
* @dev Returns the largest of two numbers.
*/
//最大值
function max(uint256 a, uint256 b) internal pure returns (uint256) {
return a >= b ? a : b;
}
/**
* @dev Returns the smallest of two numbers.
*/
//最小值
function min(uint256 a, uint256 b) internal pure returns (uint256) {
return a < b ? a : b;
}
/**
* @dev Returns the average of two numbers. The result is rounded towards
* zero.
*/
//取两数平均数,向下取整
function average(uint256 a, uint256 b) internal pure returns (uint256) {
// (a + b) / 2 can overflow, so we distribute.
return (a / 2) + (b / 2) + (((a % 2) + (b % 2)) / 2);
}
/**
* @dev Returns the ceiling of the division of two numbers.
*
* This differs from standard division with `/` in that it rounds up instead
* of rounding down.
*/
//整除向上取整(整除+1)
function ceilDiv(uint256 a, uint256 b) internal pure returns (uint256) {
// (a + b - 1) / b can overflow on addition, so we distribute.
return a / b + (a % b == 0 ? 0 : 1);
}
}
2.2 SafeCast.sol
这个库合约是解决了类型转换时(toInt256/128/64/32/16/8和toUint256/224/128/96/64/32/16/8)的溢出问题,溢出时会回滚到原始数据。
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
* @dev Wrappers over Solidity's uintXX/intXX casting operators with added overflow
* checks.
*
* Downcasting from uint256/int256 in Solidity does not revert on overflow. This can
* easily result in undesired exploitation or bugs, since developers usually
* assume that overflows raise errors. `SafeCast` restores this intuition by
* reverting the transaction when such an operation overflows.
*
* Using this library instead of the unchecked operations eliminates an entire
* class of bugs, so it's recommended to use it always.
*
* Can be combined with {SafeMath} and {SignedSafeMath} to extend it to smaller types, by performing
* all math on `uint256` and `int256` and then downcasting.
*/
/*
包装器在 Solidity 的 uintXX/intXX 转换运算符上添加溢出检查。
*
*在 Solidity 中从 uint256/int256 向下转换不会在溢出时恢复。这个可以容易导致不受欢迎的漏洞或bug,因为开发人员通常
*假设溢出会引发错误。当此类操作溢出时, “SafeCast”通过回滚交易恢复了这种直觉。
*
*使用这个库而不是未经检查的操作消除了整个这一类的错误,因此建议始终使用它。
*
*可以结合 {SafeMath} 和 {SignedSafeMath} 将其扩展到更小的类型,通过执行所有关于 `uint256` 和 `int256` 的数学运算,然后向下转型。 */
library SafeCast {
/**
* @dev Returns the downcasted uint224 from uint256, reverting on
* overflow (when the input is greater than largest uint224).
*
* Counterpart to Solidity's `uint224` operator.
*
* Requirements:
*
* - input must fit into 224 bits
*/
function toUint224(uint256 value) internal pure returns (uint224) {
require(value <= type(uint224).max, "SafeCast: value doesn't fit in 224 bits");
return uint224(value);
}
/**
* @dev Returns the downcasted uint128 from uint256, reverting on
* overflow (when the input is greater than largest uint128).
*
* Counterpart to Solidity's `uint128` operator.
*
* Requirements:
*
* - input must fit into 128 bits
*/
function toUint128(uint256 value) internal pure returns (uint128) {
require(value <= type(uint128).max, "SafeCast: value doesn't fit in 128 bits");
return uint128(value);
}
/**
* @dev Returns the downcasted uint96 from uint256, reverting on
* overflow (when the input is greater than largest uint96).
*
* Counterpart to Solidity's `uint96` operator.
*
* Requirements:
*
* - input must fit into 96 bits
*/
function toUint96(uint256 value) internal pure returns (uint96) {
require(value <= type(uint96).max, "SafeCast: value doesn't fit in 96 bits");
return uint96(value);
}
/**
* @dev Returns the downcasted uint64 from uint256, reverting on
* overflow (when the input is greater than largest uint64).
*
* Counterpart to Solidity's `uint64` operator.
*
* Requirements:
*
* - input must fit into 64 bits
*/
function toUint64(uint256 value) internal pure returns (uint64) {
require(value <= type(uint64).max, "SafeCast: value doesn't fit in 64 bits");
return uint64(value);
}
/**
* @dev Returns the downcasted uint32 from uint256, reverting on
* overflow (when the input is greater than largest uint32).
*
* Counterpart to Solidity's `uint32` operator.
*
* Requirements:
*
* - input must fit into 32 bits
*/
function toUint32(uint256 value) internal pure returns (uint32) {
require(value <= type(uint32).max, "SafeCast: value doesn't fit in 32 bits");
return uint32(value);
}
/**
* @dev Returns the downcasted uint16 from uint256, reverting on
* overflow (when the input is greater than largest uint16).
*
* Counterpart to Solidity's `uint16` operator.
*
* Requirements:
*
* - input must fit into 16 bits
*/
function toUint16(uint256 value) internal pure returns (uint16) {
require(value <= type(uint16).max, "SafeCast: value doesn't fit in 16 bits");
return uint16(value);
}
/**
* @dev Returns the downcasted uint8 from uint256, reverting on
* overflow (when the input is greater than largest uint8).
*
* Counterpart to Solidity's `uint8` operator.
*
* Requirements:
*
* - input must fit into 8 bits.
*/
function toUint8(uint256 value) internal pure returns (uint8) {
require(value <= type(uint8).max, "SafeCast: value doesn't fit in 8 bits");
return uint8(value);
}
/**
* @dev Converts a signed int256 into an unsigned uint256.
*
* Requirements:
*
* - input must be greater than or equal to 0.
*/
function toUint256(int256 value) internal pure returns (uint256) {
require(value >= 0, "SafeCast: value must be positive");
return uint256(value);
}
/**
* @dev Returns the downcasted int128 from int256, reverting on
* overflow (when the input is less than smallest int128 or
* greater than largest int128).
*
* Counterpart to Solidity's `int128` operator.
*
* Requirements:
*
* - input must fit into 128 bits
*
* _Available since v3.1._
*/
function toInt128(int256 value) internal pure returns (int128) {
require(value >= type(int128).min && value <= type(int128).max, "SafeCast: value doesn't fit in 128 bits");
return int128(value);
}
/**
* @dev Returns the downcasted int64 from int256, reverting on
* overflow (when the input is less than smallest int64 or
* greater than largest int64).
*
* Counterpart to Solidity's `int64` operator.
*
* Requirements:
*
* - input must fit into 64 bits
*
* _Available since v3.1._
*/
function toInt64(int256 value) internal pure returns (int64) {
require(value >= type(int64).min && value <= type(int64).max, "SafeCast: value doesn't fit in 64 bits");
return int64(value);
}
/**
* @dev Returns the downcasted int32 from int256, reverting on
* overflow (when the input is less than smallest int32 or
* greater than largest int32).
*
* Counterpart to Solidity's `int32` operator.
*
* Requirements:
*
* - input must fit into 32 bits
*
* _Available since v3.1._
*/
function toInt32(int256 value) internal pure returns (int32) {
require(value >= type(int32).min && value <= type(int32).max, "SafeCast: value doesn't fit in 32 bits");
return int32(value);
}
/**
* @dev Returns the downcasted int16 from int256, reverting on
* overflow (when the input is less than smallest int16 or
* greater than largest int16).
*
* Counterpart to Solidity's `int16` operator.
*
* Requirements:
*
* - input must fit into 16 bits
*
* _Available since v3.1._
*/
function toInt16(int256 value) internal pure returns (int16) {
require(value >= type(int16).min && value <= type(int16).max, "SafeCast: value doesn't fit in 16 bits");
return int16(value);
}
/**
* @dev Returns the downcasted int8 from int256, reverting on
* overflow (when the input is less than smallest int8 or
* greater than largest int8).
*
* Counterpart to Solidity's `int8` operator.
*
* Requirements:
*
* - input must fit into 8 bits.
*
* _Available since v3.1._
*/
function toInt8(int256 value) internal pure returns (int8) {
require(value >= type(int8).min && value <= type(int8).max, "SafeCast: value doesn't fit in 8 bits");
return int8(value);
}
/**
* @dev Converts an unsigned uint256 into a signed int256.
*
* Requirements:
*
* - input must be less than or equal to maxInt256.
*/
function toInt256(uint256 value) internal pure returns (int256) {
// Note: Unsafe cast below is okay because `type(int256).max` is guaranteed to be positive
require(value <= uint256(type(int256).max), "SafeCast: value doesn't fit in an int256");
return int256(value);
}
}
2.3 SafeMath
大家肯定听说过这个库,大名顶顶的TheDAO(还是美链)事件就是因为溢出,所以千万不能忽视这个问题.(我当时写项目的时候图省事就没用safemath库,然后面试官看我代码问我为什么不用。。。。。。后来我就先导库了)
永远不要直接使用算术运算符例如:+、-、*、/ 进行数学计算,除非你了解如何检查溢出漏洞,否则就没法保证这些算术计算的安全性。
SafeMath库的作用是帮我们进行算术运中进行必要的检查,避免代码中因算术运算(如溢出)而引入漏洞。
值得一提的是:从 Solidity 0.8 开始不再需要 SafeMath
。编译器现在内置了溢出检查。
但是我看了现在的库合约,比之前多了tryAdd,trySub等函数,并且有一些更节省Gas的用法,所以说还是可以继续用的。
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.
/**
* @dev Wrappers over Solidity's arithmetic operations.
*
* NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
* now has built in overflow checking.
*/
//从 Solidity 0.8 开始不再需要 `SafeMath`。编译器现在内置了溢出检查。
library SafeMath {
/**
* @dev Returns the addition of two unsigned integers, with an overflow flag.
*
* _Available since v3.4._
*/
function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
unchecked {
uint256 c = a + b;
if (c < a) return (false, 0);
return (true, c);
}
}
/**
* @dev Returns the substraction of two unsigned integers, with an overflow flag.
*
* _Available since v3.4._
*/
function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
unchecked {
if (b > a) return (false, 0);
return (true, a - b);
}
}
/**
* @dev Returns the multiplication of two unsigned integers, with an overflow flag.
*
* _Available since v3.4._
*/
function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
unchecked {
// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
// benefit is lost if 'b' is also tested.
// See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
if (a == 0) return (true, 0);
uint256 c = a * b;
if (c / a != b) return (false, 0);
return (true, c);
}
}
/**
* @dev Returns the division of two unsigned integers, with a division by zero flag.
*
* _Available since v3.4._
*/
function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
unchecked {
if (b == 0) return (false, 0);
return (true, a / b);
}
}
/**
* @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
*
* _Available since v3.4._
*/
function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
unchecked {
if (b == 0) return (false, 0);
return (true, a % b);
}
}
/**
* @dev Returns the addition of two unsigned integers, reverting on
* overflow.
*
* Counterpart to Solidity's `+` operator.
*
* Requirements:
*
* - Addition cannot overflow.
*/
function add(uint256 a, uint256 b) internal pure returns (uint256) {
return a + b;
}
/**
* @dev Returns the subtraction of two unsigned integers, reverting on
* overflow (when the result is negative).
*
* Counterpart to Solidity's `-` operator.
*
* Requirements:
*
* - Subtraction cannot overflow.
*/
function sub(uint256 a, uint256 b) internal pure returns (uint256) {
return a - b;
}
/**
* @dev Returns the multiplication of two unsigned integers, reverting on
* overflow.
*
* Counterpart to Solidity's `*` operator.
*
* Requirements:
*
* - Multiplication cannot overflow.
*/
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
return a * b;
}
/**
* @dev Returns the integer division of two unsigned integers, reverting on
* division by zero. The result is rounded towards zero.
*
* Counterpart to Solidity's `/` operator.
*
* Requirements:
*
* - The divisor cannot be zero.
*/
function div(uint256 a, uint256 b) internal pure returns (uint256) {
return a / b;
}
/**
* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
* reverting when dividing by zero.
*
* Counterpart to Solidity's `%` operator. This function uses a `revert`
* opcode (which leaves remaining gas untouched) while Solidity uses an
* invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
*
* - The divisor cannot be zero.
*/
function mod(uint256 a, uint256 b) internal pure returns (uint256) {
return a % b;
}
/**
* @dev Returns the subtraction of two unsigned integers, reverting with custom message on
* overflow (when the result is negative).
*
* CAUTION: This function is deprecated because it requires allocating memory for the error
* message unnecessarily. For custom revert reasons use {trySub}.
*
* Counterpart to Solidity's `-` operator.
*
* Requirements:
*
* - Subtraction cannot overflow.
*/
function sub(
uint256 a,
uint256 b,
string memory errorMessage
) internal pure returns (uint256) {
unchecked {
require(b <= a, errorMessage);
return a - b;
}
}
/**
* @dev Returns the integer division of two unsigned integers, reverting with custom message on
* division by zero. The result is rounded towards zero.
*
* Counterpart to Solidity's `/` operator. Note: this function uses a
* `revert` opcode (which leaves remaining gas untouched) while Solidity
* uses an invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
*
* - The divisor cannot be zero.
*/
function div(
uint256 a,
uint256 b,
string memory errorMessage
) internal pure returns (uint256) {
unchecked {
require(b > 0, errorMessage);
return a / b;
}
}
/**
* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
* reverting with custom message when dividing by zero.
*
* CAUTION: This function is deprecated because it requires allocating memory for the error
* message unnecessarily. For custom revert reasons use {tryMod}.
*
* Counterpart to Solidity's `%` operator. This function uses a `revert`
* opcode (which leaves remaining gas untouched) while Solidity uses an
* invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
*
* - The divisor cannot be zero.
*/
function mod(
uint256 a,
uint256 b,
string memory errorMessage
) internal pure returns (uint256) {
unchecked {
require(b > 0, errorMessage);
return a % b;
}
}
}
2.4 SignedSafeMath.sol
这个是有符号数的检查。注意事项和2.3一样
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
/**
* @dev Wrappers over Solidity's arithmetic operations.
*
* NOTE: `SignedSafeMath` is no longer needed starting with Solidity 0.8. The compiler
* now has built in overflow checking.
*/
library SignedSafeMath {
/**
* @dev Returns the multiplication of two signed integers, reverting on
* overflow.
*
* Counterpart to Solidity's `*` operator.
*
* Requirements:
*
* - Multiplication cannot overflow.
*/
function mul(int256 a, int256 b) internal pure returns (int256) {
return a * b;
}
/**
* @dev Returns the integer division of two signed integers. Reverts on
* division by zero. The result is rounded towards zero.
*
* Counterpart to Solidity's `/` operator.
*
* Requirements:
*
* - The divisor cannot be zero.
*/
function div(int256 a, int256 b) internal pure returns (int256) {
return a / b;
}
/**
* @dev Returns the subtraction of two signed integers, reverting on
* overflow.
*
* Counterpart to Solidity's `-` operator.
*
* Requirements:
*
* - Subtraction cannot overflow.
*/
function sub(int256 a, int256 b) internal pure returns (int256) {
return a - b;
}
/**
* @dev Returns the addition of two signed integers, reverting on
* overflow.
*
* Counterpart to Solidity's `+` operator.
*
* Requirements:
*
* - Addition cannot overflow.
*/
function add(int256 a, int256 b) internal pure returns (int256) {
return a + b;
}
}
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