YFI vs AMPL stacking contract. One is the contract used by YFI for token distribution. The other is the contract used by YAM to distribute using AMPL liquidity tokens.

YFI_vs_AMPL_stacking.diff

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>  *Submitted for verification at Etherscan.io on 2020-08-11
>  */
> 
> /**
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< * Synthetix: YFIRewards.sol
---
> * Synthetix: YAMRewards.sol
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<     address rewardDistribution;
---
>     address public rewardDistribution;
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> interface YAM {
>     function yamsScalingFactor() external returns (uint256);
> }
> 
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<     IERC20 public y = IERC20(0xdF5e0e81Dff6FAF3A7e52BA697820c5e32D806A8);
---
>     IERC20 public ampl_eth_uni_lp = IERC20(
>         0xc5be99A02C6857f9Eac67BbCE58DF5572498F40c
>     );
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<         y.safeTransferFrom(msg.sender, address(this), amount);
---
>         ampl_eth_uni_lp.safeTransferFrom(msg.sender, address(this), amount);
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<         y.safeTransfer(msg.sender, amount);
---
>         ampl_eth_uni_lp.safeTransfer(msg.sender, amount);
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< contract YearnRewards is LPTokenWrapper, IRewardDistributionRecipient {
<     IERC20 public yfi = IERC20(0x0bc529c00C6401aEF6D220BE8C6Ea1667F6Ad93e);
<     uint256 public constant DURATION = 7 days;
---
> contract YAMAMPLPool is LPTokenWrapper, IRewardDistributionRecipient {
>     IERC20 public yam = IERC20(0x0e2298E3B3390e3b945a5456fBf59eCc3f55DA16);
>     uint256 public constant DURATION = 625000; // ~7 1/4 days
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>     uint256 public starttime = 1597172400; // 2020-08-11 19:00:00 (UTC UTC +00:00)
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>     modifier checkStart() {
>         require(block.timestamp >= starttime, "not start");
>         _;
>     }
> 
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<     function stake(uint256 amount) public updateReward(msg.sender) {
---
>     function stake(uint256 amount) public updateReward(msg.sender) checkStart {
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<     function withdraw(uint256 amount) public updateReward(msg.sender) {
---
>     function withdraw(uint256 amount)
>         public
>         updateReward(msg.sender)
>         checkStart
>     {
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<     function getReward() public updateReward(msg.sender) {
---
>     function getReward() public updateReward(msg.sender) checkStart {
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<             yfi.safeTransfer(msg.sender, reward);
<             emit RewardPaid(msg.sender, reward);
---
>             uint256 scalingFactor = YAM(address(yam)).yamsScalingFactor();
>             uint256 trueReward = reward.mul(scalingFactor).div(10**18);
>             yam.safeTransfer(msg.sender, trueReward);
>             emit RewardPaid(msg.sender, trueReward);
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<         if (block.timestamp >= periodFinish) {
<             rewardRate = reward.div(DURATION);
---
>         if (block.timestamp > starttime) {
>             if (block.timestamp >= periodFinish) {
>                 rewardRate = reward.div(DURATION);
>             } else {
>                 uint256 remaining = periodFinish.sub(block.timestamp);
>                 uint256 leftover = remaining.mul(rewardRate);
>                 rewardRate = reward.add(leftover).div(DURATION);
>             }
>             lastUpdateTime = block.timestamp;
>             periodFinish = block.timestamp.add(DURATION);
>             emit RewardAdded(reward);
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<             uint256 remaining = periodFinish.sub(block.timestamp);
<             uint256 leftover = remaining.mul(rewardRate);
<             rewardRate = reward.add(leftover).div(DURATION);
---
>             rewardRate = reward.div(DURATION);
>             lastUpdateTime = starttime;
>             periodFinish = starttime.add(DURATION);
>             emit RewardAdded(reward);
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<         lastUpdateTime = block.timestamp;
<         periodFinish = block.timestamp.add(DURATION);
<         emit RewardAdded(reward);