> ## 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.

# GPv2Trade API

> Trade library API for encoding and decoding trade data in settlement batches

# GPv2Trade API

The `GPv2Trade` library is a Solidity utility for encoding and decoding trade data in settlement batches, enabling gas-efficient batch settlements.

## Data Structure

```solidity theme={null}
struct Data {
    uint256 sellTokenIndex;
    uint256 buyTokenIndex;
    address receiver;
    uint256 sellAmount;
    uint256 buyAmount;
    uint32 validTo;
    bytes32 appData;
    uint256 feeAmount;
    uint256 flags;
    uint256 executedAmount;
    bytes signature;
}
```

Rather than storing full token addresses, the struct uses an index into the tokens array for sell and buy tokens to reduce gas costs.

## Functions

### extractOrder

Converts trade data into a full order struct while extracting the signing scheme from packed flags.

```solidity theme={null}
function extractOrder(
    Data calldata trade,
    IERC20[] calldata tokens
) internal pure returns (
    GPv2Order.Data memory order,
    GPv2Signing.Scheme signingScheme
);
```

### extractFlags

Unpacks a single `uint256` value into separate order parameters.

```solidity theme={null}
function extractFlags(
    uint256 flags
) internal pure returns (
    bytes32 kind,
    bool partiallyFillable,
    bytes32 sellTokenBalance,
    bytes32 buyTokenBalance,
    GPv2Signing.Scheme signingScheme
);
```

## Flag Encoding

The library uses a bitfield approach where individual bits represent different order properties:

| Bit(s) | 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 `0x00` represents the most common case: a fill-or-kill sell order by an externally owned account using EIP-712 signatures.

## Supported Signing Schemes

| Scheme    | Value  | Description                      |
| --------- | ------ | -------------------------------- |
| EIP-712   | `0b00` | Standard typed data signing      |
| eth\_sign | `0b01` | Legacy message signing           |
| EIP-1271  | `0b10` | Smart contract wallet validation |
| PreSign   | `0b11` | On-chain pre-approval            |

## Gas Efficiency

The encoding reduces calldata costs by:

* Using token indices instead of full addresses
* Packing multiple values into single storage slots
* Optimizing for zero bytes in calldata (cheaper on Ethereum)