> For the complete documentation index, see [llms.txt](https://docs.rigoblock.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rigoblock.com/solidity-api-reference/protocol/libraries/crosschainlib.md).

# CrosschainLib

## CrosschainLib

Provides utilities for validating bridgeable token pairs, handling BSC decimal conversions, and resolving Across handler addresses.

*Used by cross-chain adapters to ensure token compatibility and proper decimal handling.*

### UnsupportedCrossChainToken

```solidity
error UnsupportedCrossChainToken()
```

### WrongDestinationToken

```solidity
error WrongDestinationToken()
```

### DEFAULT\_MULTICALL\_HANDLER

```solidity
address DEFAULT_MULTICALL_HANDLER
```

Across MulticallHandler addresses

### BSC\_MULTICALL\_HANDLER

```solidity
address BSC_MULTICALL_HANDLER
```

### isAllowedCrosschainToken

```solidity
function isAllowedCrosschainToken(address token) internal view returns (bool)
```

Check if a token is allowed for cross-chain operations on the current chain.

#### Parameters

| Name  | Type    | Description                 |
| ----- | ------- | --------------------------- |
| token | address | The token address to check. |

#### Return Values

| Name | Type | Description                                              |
| ---- | ---- | -------------------------------------------------------- |
| \[0] | bool | True if the token is allowed for cross-chain operations. |

### applyBscDecimalConversion

```solidity
function applyBscDecimalConversion(address inputToken, address outputToken, uint256 amount) internal pure returns (uint256)
```

Applies BSC decimal conversion for USDC/USDT (18 decimals on BSC vs 6 on other chains).

*Handles bidirectional conversion to ensure exact cross-chain value calculation.*

#### Parameters

| Name        | Type    | Description                               |
| ----------- | ------- | ----------------------------------------- |
| inputToken  | address | Source token address.                     |
| outputToken | address | Destination token address.                |
| amount      | uint256 | Original amount in source chain decimals. |

#### Return Values

| Name | Type    | Description                                                           |
| ---- | ------- | --------------------------------------------------------------------- |
| \[0] | uint256 | Normalized amount for correct cross-chain virtual supply calculation. |

### getAcrossHandler

```solidity
function getAcrossHandler(uint256 chainId) internal pure returns (address handler)
```

Get the appropriate Across MulticallHandler address for a given chain.

*BSC (chain ID 56) uses a different handler than other chains.*

#### Parameters

| Name    | Type    | Description               |
| ------- | ------- | ------------------------- |
| chainId | uint256 | The destination chain ID. |

#### Return Values

| Name    | Type    | Description                                           |
| ------- | ------- | ----------------------------------------------------- |
| handler | address | The MulticallHandler address for the specified chain. |

### validateBridgeableTokenPair

```solidity
function validateBridgeableTokenPair(address inputToken, address outputToken) internal pure
```

Validates that input and output tokens are compatible for cross-chain bridging.

*Only allows bridging between tokens of the same type (USDC↔USDC, USDT↔USDT, etc.).*

#### Parameters

| Name        | Type    | Description                |
| ----------- | ------- | -------------------------- |
| inputToken  | address | Source token address.      |
| outputToken | address | Destination token address. |