# EPF - Update 8 & 9

## tl;dr

* Opened PR: [0xprivateChaos/grandine-zk#1](https://github.com/0xprivateChaos/grandine-zk/pull/1)
* Added a **guest** **program** for Zisk under `guest/zisk/`
* Implemented logic in `build.rs` to serialize and write **BeaconState** and **SignedBeaconBlock** into `build/input.bin`
* The guest program now reads from `build/input.bin` for execution

## Details

The guest program (`main.rs`) performs the following steps:

1. Reads serialized input (`BeaconState` + `SignedBeaconBlock`).
2. Loads configuration using `Config::pectra_devnet_6()`.
3. Calls `read_block_and_state()` to deserialize state, block, and cache.
4. Executes `state_transition()` to update the beacon state.
5. Computes the resulting state root using `hash_tree_root()`.
6. Writes the state root to the output, 4 bytes at a time.

fn main() {
    let input = read_input();
    let config = Config::pectra_devnet_6();
    let (block, mut state, cache) =
        read_block_and_state::<Mainnet>(&config, &input).expect("Failed to read input");

    state_transition(&config, &cache, &mut state, &block).expect("State transition failed");

    let root = state.hash_tree_root();
    for i in 0..8 {
        let word = u32::from_le_bytes(root.0[i * 4..(i + 1) * 4].try_into().unwrap());
        set_output(i, word);
    }
}

### Current Status

* Building guest program manually using:

  cargo-zisk build --release

* Hitting a **linter error**, which needs to be fixed before moving forward.

## Next Week

* Connect **host** and **guest** so they work together end-to-end.