# FeeHelper

[Git Source](https://github.com/traderjoe-xyz/joe-v2/blob/16f011d25e6bf6d0a0c479974345b623d491104f/src/libraries/FeeHelper.sol)

**Author:**\
Trader Joe

This library contains functions to calculate fees

## Functions

### verifyFee

*Modifier to check that the fee is not too large*

```solidity
modifier verifyFee(uint128 fee);
```

**Parameters**

| Name  | Type      | Description |
| ----- | --------- | ----------- |
| `fee` | `uint128` | The fee     |

### verifyProtocolShare

*Modifier to check that the protocol share is not too large*

```solidity
modifier verifyProtocolShare(uint128 protocolShare);
```

**Parameters**

| Name            | Type      | Description        |
| --------------- | --------- | ------------------ |
| `protocolShare` | `uint128` | The protocol share |

### getFeeAmountFrom

*Calculates the fee amount from the amount with fees, rounding up*

```solidity
function getFeeAmountFrom(uint128 amountWithFees, uint128 totalFee)
    internal
    pure
    verifyFee(totalFee)
    returns (uint128);
```

**Parameters**

| Name             | Type      | Description          |
| ---------------- | --------- | -------------------- |
| `amountWithFees` | `uint128` | The amount with fees |
| `totalFee`       | `uint128` | The total fee        |

**Returns**

| Name     | Type      | Description              |
| -------- | --------- | ------------------------ |
| `<none>` | `uint128` | feeAmount The fee amount |

### getFeeAmount

*Calculates the fee amount that will be charged, rounding up*

```solidity
function getFeeAmount(uint128 amount, uint128 totalFee) internal pure verifyFee(totalFee) returns (uint128);
```

**Parameters**

| Name       | Type      | Description   |
| ---------- | --------- | ------------- |
| `amount`   | `uint128` | The amount    |
| `totalFee` | `uint128` | The total fee |

**Returns**

| Name     | Type      | Description              |
| -------- | --------- | ------------------------ |
| `<none>` | `uint128` | feeAmount The fee amount |

### getCompositionFee

*Calculates the composition fee amount from the amount with fees, rounding down*

```solidity
function getCompositionFee(uint128 amountWithFees, uint128 totalFee)
    internal
    pure
    verifyFee(totalFee)
    returns (uint128);
```

**Parameters**

| Name             | Type      | Description          |
| ---------------- | --------- | -------------------- |
| `amountWithFees` | `uint128` | The amount with fees |
| `totalFee`       | `uint128` | The total fee        |

**Returns**

| Name     | Type      | Description          |
| -------- | --------- | -------------------- |
| `<none>` | `uint128` | The amount with fees |

### getProtocolFeeAmount

*Calculates the protocol fee amount from the fee amount and the protocol share, rounding down*

```solidity
function getProtocolFeeAmount(uint128 feeAmount, uint128 protocolShare)
    internal
    pure
    verifyProtocolShare(protocolShare)
    returns (uint128);
```

**Parameters**

| Name            | Type      | Description        |
| --------------- | --------- | ------------------ |
| `feeAmount`     | `uint128` | The fee amount     |
| `protocolShare` | `uint128` | The protocol share |

**Returns**

| Name     | Type      | Description                               |
| -------- | --------- | ----------------------------------------- |
| `<none>` | `uint128` | protocolFeeAmount The protocol fee amount |

### \_verifyFee

*Internal function to check that the fee is not too large*

```solidity
function _verifyFee(uint128 fee) private pure;
```

**Parameters**

| Name  | Type      | Description |
| ----- | --------- | ----------- |
| `fee` | `uint128` | The fee     |

## Errors

### FeeHelper\_\_FeeTooLarge

```solidity
error FeeHelper__FeeTooLarge();
```

### FeeHelper\_\_ProtocolShareTooLarge

```solidity
error FeeHelper__ProtocolShareTooLarge();
```


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