Gnosis的ConditionalTokens解读

biakia
更新于 2023-01-31 14:13
阅读 1566

ConditionalTokens是一种基于ERC1155的代币，用于预测市场。对于一个预测问题，往往有多个选项，比如股市明天的走势，就有涨、平、跌三种情况，ConditionalTokens可以提供这三种情况，并基于Oracle进行预测结果的回写

# 1. 原理
ConditionalTokens是一种基于ERC1155的代币，用于预测市场。对于一个预测问题，往往有多个选项，比如股市明天的走势，就有涨、平、跌三种情况，ConditionalTokens可以提供这三种情况，并基于Oracle进行预测结果的回写。

# 2. 源代码
https://github.com/gnosis/conditional-tokens-contracts/blob/master/contracts/ConditionalTokens.sol

```solidity
pragma solidity ^0.5.1;
import { IERC20 } from "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";
import { ERC1155 } from "./ERC1155/ERC1155.sol";
import { CTHelpers } from "./CTHelpers.sol";

contract ConditionalTokens is ERC1155 {

/// @dev Emitted upon the successful preparation of a condition.
    /// @param conditionId The condition's ID. This ID may be derived from the other three parameters via ``keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount))``.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    event ConditionPreparation(
        bytes32 indexed conditionId,
        address indexed oracle,
        bytes32 indexed questionId,
        uint outcomeSlotCount
    );

event ConditionResolution(
        bytes32 indexed conditionId,
        address indexed oracle,
        bytes32 indexed questionId,
        uint outcomeSlotCount,
        uint[] payoutNumerators
    );

/// @dev Emitted when a position is successfully split.
    event PositionSplit(
        address indexed stakeholder,
        IERC20 collateralToken,
        bytes32 indexed parentCollectionId,
        bytes32 indexed conditionId,
        uint[] partition,
        uint amount
    );
    /// @dev Emitted when positions are successfully merged.
    event PositionsMerge(
        address indexed stakeholder,
        IERC20 collateralToken,
        bytes32 indexed parentCollectionId,
        bytes32 indexed conditionId,
        uint[] partition,
        uint amount
    );
    event PayoutRedemption(
        address indexed redeemer,
        IERC20 indexed collateralToken,
        bytes32 indexed parentCollectionId,
        bytes32 conditionId,
        uint[] indexSets,
        uint payout
    );

/// Mapping key is an condition ID. Value represents numerators of the payout vector associated with the condition. This array is initialized with a length equal to the outcome slot count. E.g. Condition with 3 outcomes [A, B, C] and two of those correct [0.5, 0.5, 0]. In Ethereum there are no decimal values, so here, 0.5 is represented by fractions like 1/2 == 0.5. That's why we need numerator and denominator values. Payout numerators are also used as a check of initialization. If the numerators array is empty (has length zero), the condition was not created/prepared. See getOutcomeSlotCount.
    mapping(bytes32 => uint[]) public payoutNumerators;
    /// Denominator is also used for checking if the condition has been resolved. If the denominator is non-zero, then the condition has been resolved.
    mapping(bytes32 => uint) public payoutDenominator;

/// @dev This function prepares a condition by initializing a payout vector associated with the condition.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    function prepareCondition(address oracle, bytes32 questionId, uint outcomeSlotCount) external {
        // Limit of 256 because we use a partition array that is a number of 256 bits.
        require(outcomeSlotCount <= 256, "too many outcome slots");
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        bytes32 conditionId = CTHelpers.getConditionId(oracle, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == 0, "condition already prepared");
        payoutNumerators[conditionId] = new uint[](outcomeSlotCount);
        emit ConditionPreparation(conditionId, oracle, questionId, outcomeSlotCount);
    }

/// @dev Called by the oracle for reporting results of conditions. Will set the payout vector for the condition with the ID ``keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount))``, where oracle is the message sender, questionId is one of the parameters of this function, and outcomeSlotCount is the length of the payouts parameter, which contains the payoutNumerators for each outcome slot of the condition.
    /// @param questionId The question ID the oracle is answering for
    /// @param payouts The oracle's answer
    function reportPayouts(bytes32 questionId, uint[] calldata payouts) external {
        uint outcomeSlotCount = payouts.length;
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        // IMPORTANT, the oracle is enforced to be the sender because it's part of the hash.
        bytes32 conditionId = CTHelpers.getConditionId(msg.sender, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == outcomeSlotCount, "condition not prepared or found");
        require(payoutDenominator[conditionId] == 0, "payout denominator already set");

uint den = 0;
        for (uint i = 0; i < outcomeSlotCount; i++) {
            uint num = payouts[i];
            den = den.add(num);

/// @dev This function splits a position. If splitting from the collateral, this contract will attempt to transfer `amount` collateral from the message sender to itself. Otherwise, this contract will burn `amount` stake held by the message sender in the position being split worth of EIP 1155 tokens. Regardless, if successful, `amount` stake will be minted in the split target positions. If any of the transfers, mints, or burns fail, the transaction will revert. The transaction will also revert if the given partition is trivial, invalid, or refers to more slots than the condition is prepared with.
    /// @param collateralToken The address of the positions' backing collateral token.
    /// @param parentCollectionId The ID of the outcome collections common to the position being split and the split target positions. May be null, in which only the collateral is shared.
    /// @param conditionId The ID of the condition to split on.
    /// @param partition An array of disjoint index sets representing a nontrivial partition of the outcome slots of the given condition. E.g. A|B and C but not A|B and B|C (is not disjoint). Each element's a number which, together with the condition, represents the outcome collection. E.g. 0b110 is A|B, 0b010 is B, etc.
    /// @param amount The amount of collateral or stake to split.
    function splitPosition(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

// For a condition with 4 outcomes fullIndexSet's 0b1111; for 5 it's 0b11111...
        uint fullIndexSet = (1 << outcomeSlotCount) - 1;
        // freeIndexSet starts as the full collection
        uint freeIndexSet = fullIndexSet;
        // This loop checks that all condition sets are disjoint (the same outcome is not part of more than 1 set)
        uint[] memory positionIds = new uint[](partition.length);
        uint[] memory amounts = new uint[](partition.length);
        for (uint i = 0; i < partition.length; i++) {
            uint indexSet = partition[i];
            require(indexSet > 0 && indexSet < fullIndexSet, "got invalid index set");
            require((indexSet & freeIndexSet) == indexSet, "partition not disjoint");
            freeIndexSet ^= indexSet;
            positionIds[i] = CTHelpers.getPositionId(collateralToken, CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));
            amounts[i] = amount;
        }

if (freeIndexSet == 0) {
            // Partitioning the full set of outcomes for the condition in this branch
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transferFrom(msg.sender, address(this), amount), "could not receive collateral tokens");
            } else {
                _burn(
                    msg.sender,
                    CTHelpers.getPositionId(collateralToken, parentCollectionId),
                    amount
                );
            }
        } else {
            // Partitioning a subset of outcomes for the condition in this branch.
            // For example, for a condition with three outcomes A, B, and C, this branch
            // allows the splitting of a position $:(A|C) to positions $:(A) and $:(C).
            _burn(
                msg.sender,
                CTHelpers.getPositionId(collateralToken,
                    CTHelpers.getCollectionId(parentCollectionId, conditionId, fullIndexSet ^ freeIndexSet)),
                amount
            );
        }

function mergePositions(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

uint fullIndexSet = (1 << outcomeSlotCount) - 1;
        uint freeIndexSet = fullIndexSet;
        uint[] memory positionIds = new uint[](partition.length);
        uint[] memory amounts = new uint[](partition.length);
        for (uint i = 0; i < partition.length; i++) {
            uint indexSet = partition[i];
            require(indexSet > 0 && indexSet < fullIndexSet, "got invalid index set");
            require((indexSet & freeIndexSet) == indexSet, "partition not disjoint");
            freeIndexSet ^= indexSet;
            positionIds[i] = CTHelpers.getPositionId(collateralToken, CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));
            amounts[i] = amount;
        }
        _batchBurn(
            msg.sender,
            positionIds,
            amounts
        );

if (freeIndexSet == 0) {
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transfer(msg.sender, amount), "could not send collateral tokens");
            } else {
                _mint(
                    msg.sender,
                    CTHelpers.getPositionId(collateralToken, parentCollectionId),
                    amount,
                    ""
                );
            }
        } else {
            _mint(
                msg.sender,
                CTHelpers.getPositionId(collateralToken,
                    CTHelpers.getCollectionId(parentCollectionId, conditionId, fullIndexSet ^ freeIndexSet)),
                amount,
                ""
            );
        }

emit PositionsMerge(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }

function redeemPositions(IERC20 collateralToken, bytes32 parentCollectionId, bytes32 conditionId, uint[] calldata indexSets) external {
        uint den = payoutDenominator[conditionId];
        require(den > 0, "result for condition not received yet");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

uint totalPayout = 0;

uint fullIndexSet = (1 << outcomeSlotCount) - 1;
        for (uint i = 0; i < indexSets.length; i++) {
            uint indexSet = indexSets[i];
            require(indexSet > 0 && indexSet < fullIndexSet, "got invalid index set");
            uint positionId = CTHelpers.getPositionId(collateralToken,
                CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));

uint payoutNumerator = 0;
            for (uint j = 0; j < outcomeSlotCount; j++) {
                if (indexSet & (1 << j) != 0) {
                    payoutNumerator = payoutNumerator.add(payoutNumerators[conditionId][j]);
                }
            }

uint payoutStake = balanceOf(msg.sender, positionId);
            if (payoutStake > 0) {
                totalPayout = totalPayout.add(payoutStake.mul(payoutNumerator).div(den));
                _burn(msg.sender, positionId, payoutStake);
            }
        }

/// @dev Gets the outcome slot count of a condition.
    /// @param conditionId ID of the condition.
    /// @return Number of outcome slots associated with a condition, or zero if condition has not been prepared yet.
    function getOutcomeSlotCount(bytes32 conditionId) external view returns (uint) {
        return payoutNumerators[conditionId].length;
    }

/// @dev Constructs a condition ID from an oracle, a question ID, and the outcome slot count for the question.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    function getConditionId(address oracle, bytes32 questionId, uint outcomeSlotCount) external pure returns (bytes32) {
        return CTHelpers.getConditionId(oracle, questionId, outcomeSlotCount);
    }

/// @dev Constructs an outcome collection ID from a parent collection and an outcome collection.
    /// @param parentCollectionId Collection ID of the parent outcome collection, or bytes32(0) if there's no parent.
    /// @param conditionId Condition ID of the outcome collection to combine with the parent outcome collection.
    /// @param indexSet Index set of the outcome collection to combine with the parent outcome collection.
    function getCollectionId(bytes32 parentCollectionId, bytes32 conditionId, uint indexSet) external view returns (bytes32) {
        return CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet);
    }

/// @dev Constructs a position ID from a collateral token and an outcome collection. These IDs are used as the ERC-1155 ID for this contract.
    /// @param collateralToken Collateral token which backs the position.
    /// @param collectionId ID of the outcome collection associated with this position.
    function getPositionId(IERC20 collateralToken, bytes32 collectionId) external pure returns (uint) {
        return CTHelpers.getPositionId(collateralToken, collectionId);
    }
}
```

# 3. 主要数据结构
```solidity
/// Mapping key is an condition ID. Value represents numerators of the payout vector associated with the condition. This array is initialized with a length equal to the outcome slot count. E.g. Condition with 3 outcomes [A, B, C] and two of those correct [0.5, 0.5, 0]. In Ethereum there are no decimal values, so here, 0.5 is represented by fractions like 1/2 == 0.5. That's why we need numerator and denominator values. Payout numerators are also used as a check of initialization. If the numerators array is empty (has length zero), the condition was not created/prepared. See getOutcomeSlotCount.
    mapping(bytes32 => uint[]) public payoutNumerators;
    /// Denominator is also used for checking if the condition has been resolved. If the denominator is non-zero, then the condition has been resolved.
    mapping(bytes32 => uint) public payoutDenominator;
```
之所以会有这两个mapping，是为了处理小数问题。比如一个预测有三个结果A,B,C，最终通过Oracle回写的结果是0.1,0.1,0.8。那么payoutNumerators就存的是conditionId => [1,1,8]，payoutDenominator存的是conditionId=>10。

# 4. 准备一个预测问题
```solidity
/// @dev This function prepares a condition by initializing a payout vector associated with the condition.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    function prepareCondition(address oracle, bytes32 questionId, uint outcomeSlotCount) external {
        // Limit of 256 because we use a partition array that is a number of 256 bits.
        require(outcomeSlotCount <= 256, "too many outcome slots");
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        bytes32 conditionId = CTHelpers.getConditionId(oracle, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == 0, "condition already prepared");
        payoutNumerators[conditionId] = new uint[](outcomeSlotCount);
        emit ConditionPreparation(conditionId, oracle, questionId, outcomeSlotCount);
    }
```
prepareCondition这个方法是用来准备一个预测问题的，入参中的oracle代表一个外部的Oracle市场地址，questionId是用户指定的预测问题唯一ID，outcomeSlotCount是这个预测问题有多少种选项。

选项最多有256个，最少有2个，选项会使用位运算，所以超过256的选项就不支持了，因为solidity最多支持256位。

接下来通过CTHelpers计算conditionId，代码如下：
```solidity
function getConditionId(address oracle, bytes32 questionId, uint outcomeSlotCount) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount));
    }
```
然后判断是否重复调用，最后初始化payoutNumerators，预留outcomeSlotCount个选项的位置。

# 5. 划分预测选项
```solidity
/// @dev This function splits a position. If splitting from the collateral, this contract will attempt to transfer `amount` collateral from the message sender to itself. Otherwise, this contract will burn `amount` stake held by the message sender in the position being split worth of EIP 1155 tokens. Regardless, if successful, `amount` stake will be minted in the split target positions. If any of the transfers, mints, or burns fail, the transaction will revert. The transaction will also revert if the given partition is trivial, invalid, or refers to more slots than the condition is prepared with.
    /// @param collateralToken The address of the positions' backing collateral token.
    /// @param parentCollectionId The ID of the outcome collections common to the position being split and the split target positions. May be null, in which only the collateral is shared.
    /// @param conditionId The ID of the condition to split on.
    /// @param partition An array of disjoint index sets representing a nontrivial partition of the outcome slots of the given condition. E.g. A|B and C but not A|B and B|C (is not disjoint). Each element's a number which, together with the condition, represents the outcome collection. E.g. 0b110 is A|B, 0b010 is B, etc.
    /// @param amount The amount of collateral or stake to split.
    function splitPosition(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

_batchMint(
            msg.sender,
            // position ID is the ERC 1155 token ID
            positionIds,
            amounts,
            ""
        );
        emit PositionSplit(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }
```
splitPosition用来划分预测选项，collateralToken是需要质押的代币，amount是质押的数量，conditionId是预测问题的ID，partition是划分的选项。以预测股市为例，有涨跌平三种，那么condition就可以划分为0x001，0x010，0x100这三个partition。

首先校验partition大于1，然后校验这个condition是否准备好。然后计算fullIndexSet，对于三种选项的condition，fullIndexSet为0x111。

然后循环partition数组，循环里面的逻辑是校验indexSet大于0，并且indexSet不重复。对应计算见下表

| i | freeIndexSet  |  indexSet    |  indexSet & freeIndexSet   |
| --- | --- | ---| --- |
| 0 | 0x111  | 0x001   | 0x001&0x111 ==> 0x001   |
| 1 | 0x110  | 0x010   | 0x010&0x110 ==> 0x010   |
| 2 | 0x100  | 0x100   | 0x100&0x100 ==> 0x100  |

如果出现了indexSet重复的现象，比如传入：0x001，0x011，0x100，那么(indexSet & freeIndexSet) == indexSet就通不过:
| i | freeIndexSet  |  indexSet    |  indexSet & freeIndexSet   |
| --- | --- | ---| --- |
| 0 | 0x111  | 0x001   | 0x001&0x111 ==> 0x001   |
| 1 | 0x110  | 0x011   | **0x110&0x011 ==> 0x010 != 0x011**   |

对于每个partition，都会使用CTHelpers生成对应的partitionId，代码如下：
```solidity
function getPositionId(IERC20 collateralToken, bytes32 collectionId) internal pure returns (uint) {
        return uint(keccak256(abi.encodePacked(collateralToken, collectionId)));
    }
```
amounts[i]会保存这个partition质押的代币数量。

接下来的逻辑分两种情况：

a、完全划分

完全划分只传入的partion与选项数一致，比如condition划分为A,B,C。如果是第一次划分，会先质押代币，然后生成LP，如果传了parentCollectionId，会把parentCollectionId对应的LP销毁，来生成新的LP，这类似于重新生成了一个condition。

b、部分划分

传入的partion只是选项的一个子集，比如condition首先划分为了B和(A|C)，然后对(A|C)进一步划分为A和C，这时候就是部分划分。

这时候会销毁(A|C)的LP，然后分别生成A和C的LP，数量都是amount。

# 6. 合并选项
```solidity
function mergePositions(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

emit PositionsMerge(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }
```
合并选项是划分选项的反向操作，也会先校验需要合并的partition的合法性，防止合并后出现选项重复。

然后会先烧掉合并的partition的LP，接下来也会分两种情况

a、完全合并

如果parentCollectionId为0x0，那么直接把质押的代币转给用户。如果传入了parentCollectionId，就给parentCollectionId对应的预测增加相应的LP。

b、部分合并

部分合并类似于A和C合并成(A|C)，会生成(A|C)的partionId，然后增加相应的LP。

# 7. 预测结果回写
```solidity
/// @dev Called by the oracle for reporting results of conditions. Will set the payout vector for the condition with the ID ``keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount))``, where oracle is the message sender, questionId is one of the parameters of this function, and outcomeSlotCount is the length of the payouts parameter, which contains the payoutNumerators for each outcome slot of the condition.
    /// @param questionId The question ID the oracle is answering for
    /// @param payouts The oracle's answer
    function reportPayouts(bytes32 questionId, uint[] calldata payouts) external {
        uint outcomeSlotCount = payouts.length;
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        // IMPORTANT, the oracle is enforced to be the sender because it's part of the hash.
        bytes32 conditionId = CTHelpers.getConditionId(msg.sender, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == outcomeSlotCount, "condition not prepared or found");
        require(payoutDenominator[conditionId] == 0, "payout denominator already set");

uint den = 0;
        for (uint i = 0; i < outcomeSlotCount; i++) {
            uint num = payouts[i];
            den = den.add(num);

require(payoutNumerators[conditionId][i] == 0, "payout numerator already set");
            payoutNumerators[conditionId][i] = num;
        }
        require(den > 0, "payout is all zeroes");
        payoutDenominator[conditionId] = den;
        emit ConditionResolution(conditionId, msg.sender, questionId, outcomeSlotCount, payoutNumerators[conditionId]);
    }
```
回传的payouts是每个选项的权重，比如[1,1,8]，reportPayouts的主要逻辑就是设置payoutNumerators和payoutDenominator，最终的结果是payoutNumerators[conditionId] = [1,1,8]，payoutDenominator[conditionId]=10.

# 8. 根据结果获取奖励
```solidity
function redeemPositions(IERC20 collateralToken, bytes32 parentCollectionId, bytes32 conditionId, uint[] calldata indexSets) external {
        uint den = payoutDenominator[conditionId];
        require(den > 0, "result for condition not received yet");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

uint totalPayout = 0;

if (totalPayout > 0) {
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transfer(msg.sender, totalPayout), "could not transfer payout to message sender");
            } else {
                _mint(msg.sender, CTHelpers.getPositionId(collateralToken, parentCollectionId), totalPayout, "");
            }
        }
        emit PayoutRedemption(msg.sender, collateralToken, parentCollectionId, conditionId, indexSets, totalPayout);
    }
```
假设用户Bob和Alice都抵押了10个代币，获取A,B,C三种预测选项的LP都是10，然后Bob把C的LP转给了Alice，作为交换，Alice把A的LP转给了Bob，这时候Bob持有20个A的LP，10个B的LP以及0个C的LP，而Alice持有0个A的LP，10个B的LP，20个C的LP。

一段时间后，Oracle回写结果为[1,1,8]，也就是A的权重是1，B的权重是1，C的权重是8。这时候Bob和Alice就可以调用redeemPositions来兑换奖励。其中Bob得到的奖励为(1 * 20+1 * 10+8 * 0)/(20 * 1+20 * 1+20 * 8) * 20 = 3个代币，Alice得到的奖励为（0 * 1+10 * 1+20 * 8)/(20 * 1+20 * 1+20 * 8) * 20 = 17个代币。Bob亏了7个代币，Alice挣了7个代币。

1. 原理

ConditionalTokens是一种基于ERC1155的代币，用于预测市场。对于一个预测问题，往往有多个选项，比如股市明天的走势，就有涨、平、跌三种情况，ConditionalTokens可以提供这三种情况，并基于Oracle进行预测结果的回写。

2. 源代码

https://github.com/gnosis/conditional-tokens-contracts/blob/master/contracts/ConditionalTokens.sol

pragma solidity ^0.5.1;
import { IERC20 } from "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";
import { ERC1155 } from "./ERC1155/ERC1155.sol";
import { CTHelpers } from "./CTHelpers.sol";

contract ConditionalTokens is ERC1155 {

    /// @dev Emitted upon the successful preparation of a condition.
    /// @param conditionId The condition's ID. This ID may be derived from the other three parameters via ``keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount))``.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    event ConditionPreparation(
        bytes32 indexed conditionId,
        address indexed oracle,
        bytes32 indexed questionId,
        uint outcomeSlotCount
    );

    event ConditionResolution(
        bytes32 indexed conditionId,
        address indexed oracle,
        bytes32 indexed questionId,
        uint outcomeSlotCount,
        uint[] payoutNumerators
    );

    /// @dev Emitted when a position is successfully split.
    event PositionSplit(
        address indexed stakeholder,
        IERC20 collateralToken,
        bytes32 indexed parentCollectionId,
        bytes32 indexed conditionId,
        uint[] partition,
        uint amount
    );
    /// @dev Emitted when positions are successfully merged.
    event PositionsMerge(
        address indexed stakeholder,
        IERC20 collateralToken,
        bytes32 indexed parentCollectionId,
        bytes32 indexed conditionId,
        uint[] partition,
        uint amount
    );
    event PayoutRedemption(
        address indexed redeemer,
        IERC20 indexed collateralToken,
        bytes32 indexed parentCollectionId,
        bytes32 conditionId,
        uint[] indexSets,
        uint payout
    );

    /// Mapping key is an condition ID. Value represents numerators of the payout vector associated with the condition. This array is initialized with a length equal to the outcome slot count. E.g. Condition with 3 outcomes [A, B, C] and two of those correct [0.5, 0.5, 0]. In Ethereum there are no decimal values, so here, 0.5 is represented by fractions like 1/2 == 0.5. That's why we need numerator and denominator values. Payout numerators are also used as a check of initialization. If the numerators array is empty (has length zero), the condition was not created/prepared. See getOutcomeSlotCount.
    mapping(bytes32 => uint[]) public payoutNumerators;
    /// Denominator is also used for checking if the condition has been resolved. If the denominator is non-zero, then the condition has been resolved.
    mapping(bytes32 => uint) public payoutDenominator;

    /// @dev This function prepares a condition by initializing a payout vector associated with the condition.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    function prepareCondition(address oracle, bytes32 questionId, uint outcomeSlotCount) external {
        // Limit of 256 because we use a partition array that is a number of 256 bits.
        require(outcomeSlotCount &lt;= 256, "too many outcome slots");
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        bytes32 conditionId = CTHelpers.getConditionId(oracle, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == 0, "condition already prepared");
        payoutNumerators[conditionId] = new uint[](outcomeSlotCount);
        emit ConditionPreparation(conditionId, oracle, questionId, outcomeSlotCount);
    }

    /// @dev Called by the oracle for reporting results of conditions. Will set the payout vector for the condition with the ID ``keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount))``, where oracle is the message sender, questionId is one of the parameters of this function, and outcomeSlotCount is the length of the payouts parameter, which contains the payoutNumerators for each outcome slot of the condition.
    /// @param questionId The question ID the oracle is answering for
    /// @param payouts The oracle's answer
    function reportPayouts(bytes32 questionId, uint[] calldata payouts) external {
        uint outcomeSlotCount = payouts.length;
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        // IMPORTANT, the oracle is enforced to be the sender because it's part of the hash.
        bytes32 conditionId = CTHelpers.getConditionId(msg.sender, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == outcomeSlotCount, "condition not prepared or found");
        require(payoutDenominator[conditionId] == 0, "payout denominator already set");

        uint den = 0;
        for (uint i = 0; i &lt; outcomeSlotCount; i++) {
            uint num = payouts[i];
            den = den.add(num);

            require(payoutNumerators[conditionId][i] == 0, "payout numerator already set");
            payoutNumerators[conditionId][i] = num;
        }
        require(den > 0, "payout is all zeroes");
        payoutDenominator[conditionId] = den;
        emit ConditionResolution(conditionId, msg.sender, questionId, outcomeSlotCount, payoutNumerators[conditionId]);
    }

    /// @dev This function splits a position. If splitting from the collateral, this contract will attempt to transfer `amount` collateral from the message sender to itself. Otherwise, this contract will burn `amount` stake held by the message sender in the position being split worth of EIP 1155 tokens. Regardless, if successful, `amount` stake will be minted in the split target positions. If any of the transfers, mints, or burns fail, the transaction will revert. The transaction will also revert if the given partition is trivial, invalid, or refers to more slots than the condition is prepared with.
    /// @param collateralToken The address of the positions' backing collateral token.
    /// @param parentCollectionId The ID of the outcome collections common to the position being split and the split target positions. May be null, in which only the collateral is shared.
    /// @param conditionId The ID of the condition to split on.
    /// @param partition An array of disjoint index sets representing a nontrivial partition of the outcome slots of the given condition. E.g. A|B and C but not A|B and B|C (is not disjoint). Each element's a number which, together with the condition, represents the outcome collection. E.g. 0b110 is A|B, 0b010 is B, etc.
    /// @param amount The amount of collateral or stake to split.
    function splitPosition(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

        // For a condition with 4 outcomes fullIndexSet's 0b1111; for 5 it's 0b11111...
        uint fullIndexSet = (1 &lt;&lt; outcomeSlotCount) - 1;
        // freeIndexSet starts as the full collection
        uint freeIndexSet = fullIndexSet;
        // This loop checks that all condition sets are disjoint (the same outcome is not part of more than 1 set)
        uint[] memory positionIds = new uint[](partition.length);
        uint[] memory amounts = new uint[](partition.length);
        for (uint i = 0; i &lt; partition.length; i++) {
            uint indexSet = partition[i];
            require(indexSet > 0 && indexSet &lt; fullIndexSet, "got invalid index set");
            require((indexSet & freeIndexSet) == indexSet, "partition not disjoint");
            freeIndexSet ^= indexSet;
            positionIds[i] = CTHelpers.getPositionId(collateralToken, CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));
            amounts[i] = amount;
        }

        if (freeIndexSet == 0) {
            // Partitioning the full set of outcomes for the condition in this branch
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transferFrom(msg.sender, address(this), amount), "could not receive collateral tokens");
            } else {
                _burn(
                    msg.sender,
                    CTHelpers.getPositionId(collateralToken, parentCollectionId),
                    amount
                );
            }
        } else {
            // Partitioning a subset of outcomes for the condition in this branch.
            // For example, for a condition with three outcomes A, B, and C, this branch
            // allows the splitting of a position $:(A|C) to positions $:(A) and $:(C).
            _burn(
                msg.sender,
                CTHelpers.getPositionId(collateralToken,
                    CTHelpers.getCollectionId(parentCollectionId, conditionId, fullIndexSet ^ freeIndexSet)),
                amount
            );
        }

        _batchMint(
            msg.sender,
            // position ID is the ERC 1155 token ID
            positionIds,
            amounts,
            ""
        );
        emit PositionSplit(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }

    function mergePositions(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

        uint fullIndexSet = (1 &lt;&lt; outcomeSlotCount) - 1;
        uint freeIndexSet = fullIndexSet;
        uint[] memory positionIds = new uint[](partition.length);
        uint[] memory amounts = new uint[](partition.length);
        for (uint i = 0; i &lt; partition.length; i++) {
            uint indexSet = partition[i];
            require(indexSet > 0 && indexSet &lt; fullIndexSet, "got invalid index set");
            require((indexSet & freeIndexSet) == indexSet, "partition not disjoint");
            freeIndexSet ^= indexSet;
            positionIds[i] = CTHelpers.getPositionId(collateralToken, CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));
            amounts[i] = amount;
        }
        _batchBurn(
            msg.sender,
            positionIds,
            amounts
        );

        if (freeIndexSet == 0) {
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transfer(msg.sender, amount), "could not send collateral tokens");
            } else {
                _mint(
                    msg.sender,
                    CTHelpers.getPositionId(collateralToken, parentCollectionId),
                    amount,
                    ""
                );
            }
        } else {
            _mint(
                msg.sender,
                CTHelpers.getPositionId(collateralToken,
                    CTHelpers.getCollectionId(parentCollectionId, conditionId, fullIndexSet ^ freeIndexSet)),
                amount,
                ""
            );
        }

        emit PositionsMerge(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }

    function redeemPositions(IERC20 collateralToken, bytes32 parentCollectionId, bytes32 conditionId, uint[] calldata indexSets) external {
        uint den = payoutDenominator[conditionId];
        require(den > 0, "result for condition not received yet");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

        uint totalPayout = 0;

        uint fullIndexSet = (1 &lt;&lt; outcomeSlotCount) - 1;
        for (uint i = 0; i &lt; indexSets.length; i++) {
            uint indexSet = indexSets[i];
            require(indexSet > 0 && indexSet &lt; fullIndexSet, "got invalid index set");
            uint positionId = CTHelpers.getPositionId(collateralToken,
                CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));

            uint payoutNumerator = 0;
            for (uint j = 0; j &lt; outcomeSlotCount; j++) {
                if (indexSet & (1 &lt;&lt; j) != 0) {
                    payoutNumerator = payoutNumerator.add(payoutNumerators[conditionId][j]);
                }
            }

            uint payoutStake = balanceOf(msg.sender, positionId);
            if (payoutStake > 0) {
                totalPayout = totalPayout.add(payoutStake.mul(payoutNumerator).div(den));
                _burn(msg.sender, positionId, payoutStake);
            }
        }

        if (totalPayout > 0) {
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transfer(msg.sender, totalPayout), "could not transfer payout to message sender");
            } else {
                _mint(msg.sender, CTHelpers.getPositionId(collateralToken, parentCollectionId), totalPayout, "");
            }
        }
        emit PayoutRedemption(msg.sender, collateralToken, parentCollectionId, conditionId, indexSets, totalPayout);
    }

    /// @dev Gets the outcome slot count of a condition.
    /// @param conditionId ID of the condition.
    /// @return Number of outcome slots associated with a condition, or zero if condition has not been prepared yet.
    function getOutcomeSlotCount(bytes32 conditionId) external view returns (uint) {
        return payoutNumerators[conditionId].length;
    }

    /// @dev Constructs a condition ID from an oracle, a question ID, and the outcome slot count for the question.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    function getConditionId(address oracle, bytes32 questionId, uint outcomeSlotCount) external pure returns (bytes32) {
        return CTHelpers.getConditionId(oracle, questionId, outcomeSlotCount);
    }

    /// @dev Constructs an outcome collection ID from a parent collection and an outcome collection.
    /// @param parentCollectionId Collection ID of the parent outcome collection, or bytes32(0) if there's no parent.
    /// @param conditionId Condition ID of the outcome collection to combine with the parent outcome collection.
    /// @param indexSet Index set of the outcome collection to combine with the parent outcome collection.
    function getCollectionId(bytes32 parentCollectionId, bytes32 conditionId, uint indexSet) external view returns (bytes32) {
        return CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet);
    }

    /// @dev Constructs a position ID from a collateral token and an outcome collection. These IDs are used as the ERC-1155 ID for this contract.
    /// @param collateralToken Collateral token which backs the position.
    /// @param collectionId ID of the outcome collection associated with this position.
    function getPositionId(IERC20 collateralToken, bytes32 collectionId) external pure returns (uint) {
        return CTHelpers.getPositionId(collateralToken, collectionId);
    }
}

3. 主要数据结构

/// Mapping key is an condition ID. Value represents numerators of the payout vector associated with the condition. This array is initialized with a length equal to the outcome slot count. E.g. Condition with 3 outcomes [A, B, C] and two of those correct [0.5, 0.5, 0]. In Ethereum there are no decimal values, so here, 0.5 is represented by fractions like 1/2 == 0.5. That's why we need numerator and denominator values. Payout numerators are also used as a check of initialization. If the numerators array is empty (has length zero), the condition was not created/prepared. See getOutcomeSlotCount.
    mapping(bytes32 => uint[]) public payoutNumerators;
    /// Denominator is also used for checking if the condition has been resolved. If the denominator is non-zero, then the condition has been resolved.
    mapping(bytes32 => uint) public payoutDenominator;

之所以会有这两个mapping，是为了处理小数问题。比如一个预测有三个结果A,B,C，最终通过Oracle回写的结果是0.1,0.1,0.8。那么payoutNumerators就存的是conditionId => [1,1,8]，payoutDenominator存的是conditionId=>10。

4. 准备一个预测问题

/// @dev This function prepares a condition by initializing a payout vector associated with the condition.
    /// @param oracle The account assigned to report the result for the prepared condition.
    /// @param questionId An identifier for the question to be answered by the oracle.
    /// @param outcomeSlotCount The number of outcome slots which should be used for this condition. Must not exceed 256.
    function prepareCondition(address oracle, bytes32 questionId, uint outcomeSlotCount) external {
        // Limit of 256 because we use a partition array that is a number of 256 bits.
        require(outcomeSlotCount &lt;= 256, "too many outcome slots");
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        bytes32 conditionId = CTHelpers.getConditionId(oracle, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == 0, "condition already prepared");
        payoutNumerators[conditionId] = new uint[](outcomeSlotCount);
        emit ConditionPreparation(conditionId, oracle, questionId, outcomeSlotCount);
    }

prepareCondition这个方法是用来准备一个预测问题的，入参中的oracle代表一个外部的Oracle市场地址，questionId是用户指定的预测问题唯一ID，outcomeSlotCount是这个预测问题有多少种选项。

选项最多有256个，最少有2个，选项会使用位运算，所以超过256的选项就不支持了，因为solidity最多支持256位。

接下来通过CTHelpers计算conditionId，代码如下：

function getConditionId(address oracle, bytes32 questionId, uint outcomeSlotCount) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount));
    }

然后判断是否重复调用，最后初始化payoutNumerators，预留outcomeSlotCount个选项的位置。

5. 划分预测选项

/// @dev This function splits a position. If splitting from the collateral, this contract will attempt to transfer `amount` collateral from the message sender to itself. Otherwise, this contract will burn `amount` stake held by the message sender in the position being split worth of EIP 1155 tokens. Regardless, if successful, `amount` stake will be minted in the split target positions. If any of the transfers, mints, or burns fail, the transaction will revert. The transaction will also revert if the given partition is trivial, invalid, or refers to more slots than the condition is prepared with.
    /// @param collateralToken The address of the positions' backing collateral token.
    /// @param parentCollectionId The ID of the outcome collections common to the position being split and the split target positions. May be null, in which only the collateral is shared.
    /// @param conditionId The ID of the condition to split on.
    /// @param partition An array of disjoint index sets representing a nontrivial partition of the outcome slots of the given condition. E.g. A|B and C but not A|B and B|C (is not disjoint). Each element's a number which, together with the condition, represents the outcome collection. E.g. 0b110 is A|B, 0b010 is B, etc.
    /// @param amount The amount of collateral or stake to split.
    function splitPosition(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

        // For a condition with 4 outcomes fullIndexSet's 0b1111; for 5 it's 0b11111...
        uint fullIndexSet = (1 &lt;&lt; outcomeSlotCount) - 1;
        // freeIndexSet starts as the full collection
        uint freeIndexSet = fullIndexSet;
        // This loop checks that all condition sets are disjoint (the same outcome is not part of more than 1 set)
        uint[] memory positionIds = new uint[](partition.length);
        uint[] memory amounts = new uint[](partition.length);
        for (uint i = 0; i &lt; partition.length; i++) {
            uint indexSet = partition[i];
            require(indexSet > 0 && indexSet &lt; fullIndexSet, "got invalid index set");
            require((indexSet & freeIndexSet) == indexSet, "partition not disjoint");
            freeIndexSet ^= indexSet;
            positionIds[i] = CTHelpers.getPositionId(collateralToken, CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));
            amounts[i] = amount;
        }

        if (freeIndexSet == 0) {
            // Partitioning the full set of outcomes for the condition in this branch
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transferFrom(msg.sender, address(this), amount), "could not receive collateral tokens");
            } else {
                _burn(
                    msg.sender,
                    CTHelpers.getPositionId(collateralToken, parentCollectionId),
                    amount
                );
            }
        } else {
            // Partitioning a subset of outcomes for the condition in this branch.
            // For example, for a condition with three outcomes A, B, and C, this branch
            // allows the splitting of a position $:(A|C) to positions $:(A) and $:(C).
            _burn(
                msg.sender,
                CTHelpers.getPositionId(collateralToken,
                    CTHelpers.getCollectionId(parentCollectionId, conditionId, fullIndexSet ^ freeIndexSet)),
                amount
            );
        }

        _batchMint(
            msg.sender,
            // position ID is the ERC 1155 token ID
            positionIds,
            amounts,
            ""
        );
        emit PositionSplit(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }

splitPosition用来划分预测选项，collateralToken是需要质押的代币，amount是质押的数量，conditionId是预测问题的ID，partition是划分的选项。以预测股市为例，有涨跌平三种，那么condition就可以划分为0x001，0x010，0x100这三个partition。

首先校验partition大于1，然后校验这个condition是否准备好。然后计算fullIndexSet，对于三种选项的condition，fullIndexSet为0x111。

然后循环partition数组，循环里面的逻辑是校验indexSet大于0，并且indexSet不重复。对应计算见下表

i	freeIndexSet	indexSet	indexSet & freeIndexSet
0	0x111	0x001	0x001&0x111 ==> 0x001
1	0x110	0x010	0x010&0x110 ==> 0x010
2	0x100	0x100	0x100&0x100 ==> 0x100

如果出现了indexSet重复的现象，比如传入：0x001，0x011，0x100，那么(indexSet & freeIndexSet) == indexSet就通不过:	i	freeIndexSet	indexSet	indexSet & freeIndexSet
0	0x111	0x001	0x001&0x111 ==> 0x001
1	0x110	0x011	0x110&0x011 ==> 0x010 != 0x011

对于每个partition，都会使用CTHelpers生成对应的partitionId，代码如下：

function getPositionId(IERC20 collateralToken, bytes32 collectionId) internal pure returns (uint) {
        return uint(keccak256(abi.encodePacked(collateralToken, collectionId)));
    }

amounts[i]会保存这个partition质押的代币数量。

接下来的逻辑分两种情况：

a、完全划分

b、部分划分

传入的partion只是选项的一个子集，比如condition首先划分为了B和(A|C)，然后对(A|C)进一步划分为A和C，这时候就是部分划分。

这时候会销毁(A|C)的LP，然后分别生成A和C的LP，数量都是amount。

6. 合并选项

function mergePositions(
        IERC20 collateralToken,
        bytes32 parentCollectionId,
        bytes32 conditionId,
        uint[] calldata partition,
        uint amount
    ) external {
        require(partition.length > 1, "got empty or singleton partition");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

        uint fullIndexSet = (1 &lt;&lt; outcomeSlotCount) - 1;
        uint freeIndexSet = fullIndexSet;
        uint[] memory positionIds = new uint[](partition.length);
        uint[] memory amounts = new uint[](partition.length);
        for (uint i = 0; i &lt; partition.length; i++) {
            uint indexSet = partition[i];
            require(indexSet > 0 && indexSet &lt; fullIndexSet, "got invalid index set");
            require((indexSet & freeIndexSet) == indexSet, "partition not disjoint");
            freeIndexSet ^= indexSet;
            positionIds[i] = CTHelpers.getPositionId(collateralToken, CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));
            amounts[i] = amount;
        }
        _batchBurn(
            msg.sender,
            positionIds,
            amounts
        );

        if (freeIndexSet == 0) {
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transfer(msg.sender, amount), "could not send collateral tokens");
            } else {
                _mint(
                    msg.sender,
                    CTHelpers.getPositionId(collateralToken, parentCollectionId),
                    amount,
                    ""
                );
            }
        } else {
            _mint(
                msg.sender,
                CTHelpers.getPositionId(collateralToken,
                    CTHelpers.getCollectionId(parentCollectionId, conditionId, fullIndexSet ^ freeIndexSet)),
                amount,
                ""
            );
        }

        emit PositionsMerge(msg.sender, collateralToken, parentCollectionId, conditionId, partition, amount);
    }

合并选项是划分选项的反向操作，也会先校验需要合并的partition的合法性，防止合并后出现选项重复。

然后会先烧掉合并的partition的LP，接下来也会分两种情况

a、完全合并

如果parentCollectionId为0x0，那么直接把质押的代币转给用户。如果传入了parentCollectionId，就给parentCollectionId对应的预测增加相应的LP。

b、部分合并

部分合并类似于A和C合并成(A|C)，会生成(A|C)的partionId，然后增加相应的LP。

7. 预测结果回写

/// @dev Called by the oracle for reporting results of conditions. Will set the payout vector for the condition with the ID ``keccak256(abi.encodePacked(oracle, questionId, outcomeSlotCount))``, where oracle is the message sender, questionId is one of the parameters of this function, and outcomeSlotCount is the length of the payouts parameter, which contains the payoutNumerators for each outcome slot of the condition.
    /// @param questionId The question ID the oracle is answering for
    /// @param payouts The oracle's answer
    function reportPayouts(bytes32 questionId, uint[] calldata payouts) external {
        uint outcomeSlotCount = payouts.length;
        require(outcomeSlotCount > 1, "there should be more than one outcome slot");
        // IMPORTANT, the oracle is enforced to be the sender because it's part of the hash.
        bytes32 conditionId = CTHelpers.getConditionId(msg.sender, questionId, outcomeSlotCount);
        require(payoutNumerators[conditionId].length == outcomeSlotCount, "condition not prepared or found");
        require(payoutDenominator[conditionId] == 0, "payout denominator already set");

        uint den = 0;
        for (uint i = 0; i &lt; outcomeSlotCount; i++) {
            uint num = payouts[i];
            den = den.add(num);

            require(payoutNumerators[conditionId][i] == 0, "payout numerator already set");
            payoutNumerators[conditionId][i] = num;
        }
        require(den > 0, "payout is all zeroes");
        payoutDenominator[conditionId] = den;
        emit ConditionResolution(conditionId, msg.sender, questionId, outcomeSlotCount, payoutNumerators[conditionId]);
    }

回传的payouts是每个选项的权重，比如[1,1,8]，reportPayouts的主要逻辑就是设置payoutNumerators和payoutDenominator，最终的结果是payoutNumerators[conditionId] = [1,1,8]，payoutDenominator[conditionId]=10.

8. 根据结果获取奖励

function redeemPositions(IERC20 collateralToken, bytes32 parentCollectionId, bytes32 conditionId, uint[] calldata indexSets) external {
        uint den = payoutDenominator[conditionId];
        require(den > 0, "result for condition not received yet");
        uint outcomeSlotCount = payoutNumerators[conditionId].length;
        require(outcomeSlotCount > 0, "condition not prepared yet");

        uint totalPayout = 0;

        uint fullIndexSet = (1 &lt;&lt; outcomeSlotCount) - 1;
        for (uint i = 0; i &lt; indexSets.length; i++) {
            uint indexSet = indexSets[i];
            require(indexSet > 0 && indexSet &lt; fullIndexSet, "got invalid index set");
            uint positionId = CTHelpers.getPositionId(collateralToken,
                CTHelpers.getCollectionId(parentCollectionId, conditionId, indexSet));

            uint payoutNumerator = 0;
            for (uint j = 0; j &lt; outcomeSlotCount; j++) {
                if (indexSet & (1 &lt;&lt; j) != 0) {
                    payoutNumerator = payoutNumerator.add(payoutNumerators[conditionId][j]);
                }
            }

            uint payoutStake = balanceOf(msg.sender, positionId);
            if (payoutStake > 0) {
                totalPayout = totalPayout.add(payoutStake.mul(payoutNumerator).div(den));
                _burn(msg.sender, positionId, payoutStake);
            }
        }

        if (totalPayout > 0) {
            if (parentCollectionId == bytes32(0)) {
                require(collateralToken.transfer(msg.sender, totalPayout), "could not transfer payout to message sender");
            } else {
                _mint(msg.sender, CTHelpers.getPositionId(collateralToken, parentCollectionId), totalPayout, "");
            }
        }
        emit PayoutRedemption(msg.sender, collateralToken, parentCollectionId, conditionId, indexSets, totalPayout);
    }

假设用户Bob和Alice都抵押了10个代币，获取A,B,C三种预测选项的LP都是10，然后Bob把C的LP转给了Alice，作为交换，Alice把A的LP转给了Bob，这时候Bob持有20个A的LP，10个B的LP以及0个C的LP，而Alice持有0个A的LP，10个B的LP，20个C的LP。

一段时间后，Oracle回写结果为[1,1,8]，也就是A的权重是1，B的权重是1，C的权重是8。这时候Bob和Alice就可以调用redeemPositions来兑换奖励。其中Bob得到的奖励为(1 20+1 10+8 0)/(20 1+20 1+20 8) 20 = 3个代币，Alice得到的奖励为（0 1+10 1+20 8)/(20 1+20 1+20 8) 20 = 17个代币。Bob亏了7个代币，Alice挣了7个代币。

原创
学分: 8
分类: Solidity
标签: Gnosis ERC1155

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