plonky2/evm/src/cpu/kernel/keccak_util.rs

/// A Keccak-f based hash.
///
/// This hash does not use standard Keccak padding, since we don't care about extra zeros at the
/// end of the code.
pub(crate) fn hash_kernel(_code: &[u8]) -> [u32; 8] {
    let state = [0u32; 50];
    // TODO: absorb code
    state[0..8].try_into().unwrap()
}

/// Like tiny-keccak's `keccakf`, but deals with `u32` limbs instead of `u64` limbs.
pub(crate) fn keccakf_u32s(_state: &mut [u32; 50]) {
    // TODO: Implement
}
Continue work on bootstrapping The kernel is hashed using a Keccak based sponge for now. We could switch to Poseidon later if our kernel grows too large. Note that we use simple zero-padding (pad0) instead of the standard pad10 rule. It's simpler, and we don't care that the prover can add extra 0s at the end of the code. The program counter can never reach those bytes, and even if it could, they'd be 0 anyway given the EVM's zero-initialization rule. In one CPU row, we can do a whole Keccak hash (via the CTL), absorbing 136 bytes. But we can't actually bootstrap that many bytes of kernel code in one row, because we're also limited by memory bandwidth. Currently we can write 4 bytes of the kernel to memory in one row. So we treat the `keccak_input_limbs` columns as a buffer. We gradually fill up this buffer, 4 bytes (one `u32` word) at a time. Every `136 / 4 = 34` rows, the buffer will be full, so at that point we activate the Keccak CTL to absorb the buffer. 2022-07-14 11:31:47 -07:00			`/// A Keccak-f based hash.`
			`///`
			`/// This hash does not use standard Keccak padding, since we don't care about extra zeros at the`
			`/// end of the code.`
			`pub(crate) fn hash_kernel(_code: &[u8]) -> [u32; 8] {`
			`let state = [0u32; 50];`
			`// TODO: absorb code`
			`state[0..8].try_into().unwrap()`
			`}`

			/// Like tiny-keccak's `keccakf`, but deals with `u32` limbs instead of `u64` limbs.
			`pub(crate) fn keccakf_u32s(_state: &mut [u32; 50]) {`
			`// TODO: Implement`
			`}`