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

<AgentInstructions>

## Submitting Feedback

If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback:

POST https://docs.ton.org/feedback

```json
{
  "path": "/foundations/messages/deploy",
  "feedback": "Description of the issue"
}
```

Only submit feedback when you have something specific and actionable to report.

</AgentInstructions>

# Deploy message

`StateInit` is a data structure sent as part of a message, either internal or incoming external, used to

* deploy a smart contract, for which it stores the initial code and data of a contract;
* [unfreeze](/foundations/status#status-transitions) a contract, where its last committed code and data are used.

This structure can be appended in-place or as a referenced cell to every message:

```tlb theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
message$_
    {X:Type}
    info:CommonMsgInfo
    init:(Maybe (Either StateInit ^StateInit))
    body:(Either X ^X)
= Message X;
```

The `StateInit` structure is defined as follows:

```tlb theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
_
    fixed_prefix_length:(Maybe (## 5))
    special:(Maybe TickTock)
    code:(Maybe ^Cell)
    data:(Maybe ^Cell)
    library:(Maybe ^Cell)
= StateInit;
```

where the fields are:

* `special`: was meant to register a smart contract for tick-tock events; now is deprecated.
* `code`: the initial code of the contract.
* `data`: the initial data of the contract.
* `library`: the initial library of the contract.
* `fixed_prefix_length`: number of most significant address bits that may differ between the deploy message destination and the address derived from `StateInit`; the remaining bits must match.

## Deploying to specific shard

Due to [the way](/foundations/shards) messages are sent between blockchain shards, the number of hops and, hence, latency depends on the distance between the shards of a source and a destination. The optimal performance is achieved when both addresses are in the same shard.

Usually, a new contract has to be deployed by a message to the exactly same address as computed out of `StateInit`'s hash, i.e. the content of `StateInit` uniquely determines the address. Any discrepancy between the address [computed](/foundations/addresses/derive) from `StateInit` and destination address of a deploy message [will result](/foundations/phases#when-the-compute-phase-is-skipped) in a failed transaction.

To deploy a contract to the desired shard, there is a `fixed_prefix_length` field in `StateInit`. It allows to specify the destination address that would slightly differ from the computed address. Only all the bits except for the first `fixed_prefix_length` have to match.

To put it more formally,

```
drop(fixed_prefix_length, addressFrom(stateInit)) = drop(fixed_prefix_length, destination)
```

where

* `drop(n, x)` drops the `n` most significant bits from a 256-bit number `x`,
* `addressFrom(s)` computes contract's address from a hash of `StateInit s`.

When `fixed_prefix_length` is zero or not set, the condition simplifies to

```
addressFrom(stateInit) = destination
```

### Example

Assume an address `D` starts with `0x5ABC...`. If there are 256 active shardchains, the first 8 bits of the address (i.e., `5A`) correspond to shard IDs.

Now, if some other contract `S` is deployed that intends to exchange messages with `D`, and computing an address from its `StateInit` results in `0x2623...`, it will be deployed by default into a shard `26`. Messages from `26` to `5A` will take 2 hops and 2 blocks to arrive at the destination.

To put `S` into the same shard as `D`, set `fixed_prefix_length` to 8 and send the deploy message to the address `0x5A23...`. Then TVM will ignore the discrepancy in the first 8 bits between the computed address (`0x2623...`) and the passed destination (`0x5A23...`), because their remaining 248 bits coincide, and `S` will be deployed into shard `5A`.

### Limits

The largest value for `fixed_prefix_length` is set in the blockchain config ([param 43](/foundations/config#param-43%3A-account-and-message-limits)), and at the moment is `8`, i.e. discrepancy in only eight bits of address can be ignored.