binius_core/constraint_system/channel.rs
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// Copyright 2024 Irreducible Inc.
//! A channel allows communication between tables.
//!
//! Note that the channel is unordered - meaning that rows are not
//! constrained to be in the same order when being pushed and pulled.
//!
//! The number of columns per channel must be fixed, but can be any
//! positive integer. Column order is guaranteed, and column values within
//! the same row must always stay together.
//!
//! A channel only ensures that the inputs and outputs match, using a
//! multiset check. If you want any kind of ordering, you have to
//! use polynomial constraints to additionally constraint this.
//!
//! The example below shows a channel with width=2, with multiple inputs
//! and outputs.
//! ```txt
//! +-+-+
//! |C|D|
//! +-+-+ +---> +-+-+
//! |A|B| | |M|N|
//! +-+-+ | +-+-+
//! |C|D| |
//! +-+-+ --+ | +-+-+
//! |E|F| | | |I|J|
//! +-+-+ | | +-+-+
//! |G|H| | | |W|X|
//! +-+-+ | | +-> +-+-+
//! | | | |A|B|
//! +-+-+ +-> /¯\¯¯¯¯¯¯¯¯¯¯¯\ --+ | +-+-+
//! |I|J| : : : ----+ |K|L|
//! +-+-+ PUSH | | channel | PULL +-+-+
//! |K|L| : : : ----+
//! +-+-+ +-> \_/___________/ --+ | +-+-+
//! |M|N| | | | |U|V|
//! +-+-+ | | | +-+-+
//! |O|P| | | | |G|H|
//! +-+-+ --+ | +-> +-+-+
//! |Q|R| | |E|F|
//! +-+-+ | +-+-+
//! |S|T| | |Q|R|
//! +-+-+ | +-+-+
//! |U|V| |
//! +-+-+ | +-+-+
//! |W|X| | |O|P|
//! +-+-+ +---> +-+-+
//! |S|T|
//! +-+-+
//! ```
use super::error::Error;
use crate::{oracle::OracleId, witness::MultilinearExtensionIndex};
use binius_field::{as_packed_field::PackScalar, underlier::UnderlierType, TowerField};
pub type ChannelId = usize;
#[derive(Debug, Clone)]
pub struct Flush {
pub oracles: Vec<OracleId>,
pub channel_id: ChannelId,
pub direction: FlushDirection,
}
#[derive(Debug, Clone)]
pub struct Boundary<F: TowerField> {
pub values: Vec<F>,
pub channel_id: ChannelId,
pub direction: FlushDirection,
}
#[derive(Debug, Clone, Copy)]
pub enum FlushDirection {
Push,
Pull,
}
pub fn validate_witness<U, F>(
witness: &MultilinearExtensionIndex<U, F>,
flushes: &[Flush],
boundaries: &[Boundary<F>],
max_channel_id: ChannelId,
) -> Result<(), Error>
where
U: UnderlierType + PackScalar<F>,
F: TowerField + Ord,
{
let mut channels = vec![Channel::<F>::new(); max_channel_id + 1];
for boundary in boundaries.iter().cloned() {
let Boundary {
channel_id,
values,
direction,
} = boundary;
if channel_id > max_channel_id {
return Err(Error::ChannelIdOutOfRange {
max: max_channel_id,
got: channel_id,
});
}
channels[channel_id].flush(&direction, values.clone())?;
}
for flush in flushes {
let Flush {
oracles,
channel_id,
direction,
} = flush;
if *channel_id > max_channel_id {
return Err(Error::ChannelIdOutOfRange {
max: max_channel_id,
got: *channel_id,
});
}
let channel = &mut channels[*channel_id];
let polys = oracles
.iter()
.map(|id| witness.get_multilin_poly(*id).unwrap())
.collect::<Vec<_>>();
// Ensure that all the polys in a single flush have the same n_vars
if let Some(first_poly) = polys.first() {
let n_vars = first_poly.n_vars();
for poly in &polys {
if poly.n_vars() != n_vars {
return Err(Error::ChannelFlushNvarsMismatch {
expected: n_vars,
got: poly.n_vars(),
});
}
}
for i in 0..(1 << n_vars) {
let values = polys
.iter()
.map(|poly| poly.evaluate_on_hypercube(i).unwrap())
.collect();
channel.flush(direction, values)?;
}
}
}
for (id, channel) in channels.iter().enumerate() {
if !channel.is_balanced() {
return Err(Error::ChannelUnbalanced { id });
}
}
Ok(())
}
#[derive(Debug, Clone)]
struct Channel<F: TowerField> {
width: Option<usize>,
pushes: Vec<Vec<F>>,
pulls: Vec<Vec<F>>,
}
impl<F: TowerField> Default for Channel<F> {
fn default() -> Self {
Self {
width: None,
pushes: Vec::new(),
pulls: Vec::new(),
}
}
}
impl<F: TowerField + Ord> Channel<F> {
fn new() -> Self {
Self::default()
}
fn flush(&mut self, direction: &FlushDirection, values: Vec<F>) -> Result<(), Error> {
if self.width.is_none() {
self.width = Some(values.len());
} else if self.width.unwrap() != values.len() {
return Err(Error::ChannelFlushWidthMismatch {
expected: self.width.unwrap(),
got: values.len(),
});
}
match direction {
FlushDirection::Pull => self.pulls.push(values),
FlushDirection::Push => self.pushes.push(values),
}
Ok(())
}
fn is_balanced(&self) -> bool {
let mut pushes = self.pushes.clone();
let mut pulls = self.pulls.clone();
pushes.sort();
pulls.sort();
pushes == pulls
}
}