Function chunk_message

bitvm/src/hash/blake3.rs:223–238

Transforms the given message into a format that BLAKE3 understands.

(message_bytes: &[u8])

/// Transforms the given message into a format that BLAKE3 understands.
fn chunk_message(message_bytes: &[u8]) -> Vec<[u8; 64]> {
    let len = message_bytes.len();
    let needed_padding_bytes = if len % 64 == 0 { 0 } else { 64 - (len % 64) };

    message_bytes
        .iter()
        .copied()
        .chain(std::iter::repeat_n(0u8, needed_padding_bytes))
        .chunks(4) // reverse 4-byte chunks
        .into_iter()
        .flat_map(|chunk| chunk.collect::<Vec<u8>>().into_iter().rev())
        .chunks(64) // collect 64-byte chunks
        .into_iter()
        .map(|mut chunk| std::array::from_fn(|_| chunk.next().unwrap()))
        .collect()
}

/// Returns a script that pushes the given message onto the stack for BLAKE3.
///