> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cow.bleu.builders/llms.txt
> Use this file to discover all available pages before exploring further.

# Core Libraries

> Specialized Solidity libraries for order handling, trade execution, and signature verification

# Core Libraries

CoW Protocol employs specialized libraries designed for gas efficiency and security, using low-level optimizations where appropriate.

## GPv2Order

Defines the complete order structure and provides utilities for order management.

### Data Structure

```solidity theme={null}
struct Data {
    IERC20 sellToken;
    IERC20 buyToken;
    address receiver;
    uint256 sellAmount;
    uint256 buyAmount;
    uint32 validTo;
    bytes32 appData;
    uint256 feeAmount;
    bytes32 kind;
    bool partiallyFillable;
    bytes32 sellTokenBalance;
    bytes32 buyTokenBalance;
}
```

### Key Functions

* `hash(Data memory order)` - Computes EIP-712 digest for signing
* `actualReceiver(Data memory order)` - Resolves recipient address (handles zero-address as owner)
* `packOrderUidParams()` - Encodes 56-byte UID (32-byte digest + 20-byte owner + 4-byte timestamp)
* `extractOrderUidParams()` - Decodes UID components

### Pre-computed Constants

```solidity theme={null}
bytes32 constant KIND_SELL = keccak256("sell");
bytes32 constant KIND_BUY = keccak256("buy");
bytes32 constant BALANCE_ERC20 = keccak256("erc20");
bytes32 constant BALANCE_EXTERNAL = keccak256("external");
bytes32 constant BALANCE_INTERNAL = keccak256("internal");
```

## GPv2Trade

Handles compact settlement representation through a flags field that encodes order parameters into a single `uint256` value.

### Flag Encoding

| Bits | Field              | Values                                                    |
| ---- | ------------------ | --------------------------------------------------------- |
| 0    | Order kind         | 0 = sell, 1 = buy                                         |
| 1    | Fill type          | 0 = fill-or-kill, 1 = partially fillable                  |
| 2-3  | Sell token balance | 00 = ERC20, 01 = external, 10 = internal                  |
| 4    | Buy token balance  | 0 = ERC20, 1 = internal                                   |
| 5-6  | Signing scheme     | 00 = EIP-712, 01 = eth\_sign, 10 = EIP-1271, 11 = PreSign |

The default value `0x00` represents the most common case: a fill-or-kill sell order by an externally owned account using EIP-712 signatures.

### Key Functions

* `extractOrder()` - Converts trade data into a full order struct
* `extractFlags()` - Unpacks flags into separate order parameters

## GPv2Interaction

Enables arbitrary contract calls during settlement using inline assembly for gas optimization.

### Data Structure

```solidity theme={null}
struct Data {
    address target;
    uint256 value;
    bytes callData;
}
```

### Key Functions

* `execute(Data calldata interaction)` - Performs the contract interaction
* `selector(Data calldata interaction)` - Extracts 4-byte function selector

### Settlement Phases

Interactions run at three distinct phases:

1. **Pre-settlement** - Setup operations like approvals
2. **Intra-settlement** - Liquidity transformations after input transfers
3. **Post-settlement** - Cleanup tasks like token unwrapping

## GPv2Signing

Supports four signature schemes:

| Scheme        | Description                           |
| ------------- | ------------------------------------- |
| **EIP-712**   | Standard typed data signing           |
| **eth\_sign** | Legacy signing with message prefix    |
| **EIP-1271**  | Smart contract signature verification |
| **PreSign**   | On-chain pre-authorization            |

### Key Features

* Careful memory management to avoid unnecessary copies
* Extensive use of `calldata` instead of `memory` for read-only data
* Domain separator includes contract address for replay protection
* Pre-computed hash constants for common types