plonky2/src/gates/gmimc.rs
2021-08-06 15:14:38 +02:00

406 lines
13 KiB
Rust

use std::sync::Arc;
use crate::field::extension_field::target::ExtensionTarget;
use crate::field::extension_field::Extendable;
use crate::field::field_types::Field;
use crate::gates::gate::Gate;
use crate::hash::gmimc::gmimc_automatic_constants;
use crate::iop::generator::{GeneratedValues, SimpleGenerator, WitnessGenerator};
use crate::iop::target::Target;
use crate::iop::wire::Wire;
use crate::iop::witness::PartialWitness;
use crate::plonk::circuit_builder::CircuitBuilder;
use crate::plonk::vars::{EvaluationTargets, EvaluationVars, EvaluationVarsBase};
/// The width of the permutation, in field elements.
const W: usize = 12;
/// Evaluates a full GMiMC permutation with 12 state elements, and writes the output to the next
/// gate's first `width` wires (which could be the input of another `GMiMCGate`).
///
/// This also has some extra features to make it suitable for efficiently verifying Merkle proofs.
/// It has a flag which can be used to swap the first four inputs with the next four, for ordering
/// sibling digests. It also has an accumulator that computes the weighted sum of these flags, for
/// computing the index of the leaf based on these swap bits.
#[derive(Debug)]
pub struct GMiMCGate<F: Extendable<D>, const D: usize, const R: usize> {
constants: Arc<[F; R]>,
}
impl<F: Extendable<D>, const D: usize, const R: usize> GMiMCGate<F, D, R> {
pub fn new(constants: Arc<[F; R]>) -> Self {
Self { constants }
}
pub fn new_automatic_constants() -> Self {
let constants = Arc::new(gmimc_automatic_constants::<F, R>());
Self::new(constants)
}
/// The wire index for the `i`th input to the permutation.
pub fn wire_input(i: usize) -> usize {
i
}
/// The wire index for the `i`th output to the permutation.
pub fn wire_output(i: usize) -> usize {
W + i
}
/// If this is set to 1, the first four inputs will be swapped with the next four inputs. This
/// is useful for ordering hashes in Merkle proofs. Otherwise, this should be set to 0.
pub const WIRE_SWAP: usize = 2 * W;
/// A wire which stores the input to the `i`th cubing.
fn wire_cubing_input(i: usize) -> usize {
2 * W + 1 + i
}
/// End of wire indices, exclusive.
fn end() -> usize {
2 * W + 1 + R
}
}
impl<F: Extendable<D>, const D: usize, const R: usize> Gate<F, D> for GMiMCGate<F, D, R> {
fn id(&self) -> String {
format!("<R={}> {:?}", R, self)
}
fn eval_unfiltered(&self, vars: EvaluationVars<F, D>) -> Vec<F::Extension> {
let mut constraints = Vec::with_capacity(self.num_constraints());
// Assert that `swap` is binary.
let swap = vars.local_wires[Self::WIRE_SWAP];
constraints.push(swap * (swap - F::Extension::ONE));
let mut state = Vec::with_capacity(12);
for i in 0..4 {
let a = vars.local_wires[i];
let b = vars.local_wires[i + 4];
state.push(a + swap * (b - a));
}
for i in 0..4 {
let a = vars.local_wires[i + 4];
let b = vars.local_wires[i];
state.push(a + swap * (b - a));
}
for i in 8..12 {
state.push(vars.local_wires[i]);
}
// Value that is implicitly added to each element.
// See https://affine.group/2020/02/starkware-challenge
let mut addition_buffer = F::Extension::ZERO;
for r in 0..R {
let active = r % W;
let cubing_input = state[active] + addition_buffer + self.constants[r].into();
let cubing_input_wire = vars.local_wires[Self::wire_cubing_input(r)];
constraints.push(cubing_input - cubing_input_wire);
let f = cubing_input_wire.cube();
addition_buffer += f;
state[active] -= f;
}
for i in 0..W {
state[i] += addition_buffer;
constraints.push(state[i] - vars.local_wires[Self::wire_output(i)]);
}
constraints
}
fn eval_unfiltered_base(&self, vars: EvaluationVarsBase<F>) -> Vec<F> {
let mut constraints = Vec::with_capacity(self.num_constraints());
// Assert that `swap` is binary.
let swap = vars.local_wires[Self::WIRE_SWAP];
constraints.push(swap * (swap - F::ONE));
let mut state = Vec::with_capacity(12);
for i in 0..4 {
let a = vars.local_wires[i];
let b = vars.local_wires[i + 4];
state.push(a + swap * (b - a));
}
for i in 0..4 {
let a = vars.local_wires[i + 4];
let b = vars.local_wires[i];
state.push(a + swap * (b - a));
}
for i in 8..12 {
state.push(vars.local_wires[i]);
}
// Value that is implicitly added to each element.
// See https://affine.group/2020/02/starkware-challenge
let mut addition_buffer = F::ZERO;
for r in 0..R {
let active = r % W;
let cubing_input = state[active] + addition_buffer + self.constants[r].into();
let cubing_input_wire = vars.local_wires[Self::wire_cubing_input(r)];
constraints.push(cubing_input - cubing_input_wire);
let f = cubing_input_wire.cube();
addition_buffer += f;
state[active] -= f;
}
for i in 0..W {
state[i] += addition_buffer;
constraints.push(state[i] - vars.local_wires[Self::wire_output(i)]);
}
constraints
}
fn eval_unfiltered_recursively(
&self,
builder: &mut CircuitBuilder<F, D>,
vars: EvaluationTargets<D>,
) -> Vec<ExtensionTarget<D>> {
let mut constraints = Vec::with_capacity(self.num_constraints());
let swap = vars.local_wires[Self::WIRE_SWAP];
constraints.push(builder.mul_sub_extension(swap, swap, swap));
let mut state = Vec::with_capacity(12);
for i in 0..4 {
let a = vars.local_wires[i];
let b = vars.local_wires[i + 4];
let delta = builder.sub_extension(b, a);
state.push(builder.mul_add_extension(swap, delta, a));
}
for i in 0..4 {
let a = vars.local_wires[i + 4];
let b = vars.local_wires[i];
let delta = builder.sub_extension(b, a);
state.push(builder.mul_add_extension(swap, delta, a));
}
for i in 8..12 {
state.push(vars.local_wires[i]);
}
// Value that is implicitly added to each element.
// See https://affine.group/2020/02/starkware-challenge
let mut addition_buffer = builder.zero_extension();
for r in 0..R {
let active = r % W;
let constant = builder.constant_extension(self.constants[r].into());
let cubing_input =
builder.add_three_extension(state[active], addition_buffer, constant);
let cubing_input_wire = vars.local_wires[Self::wire_cubing_input(r)];
constraints.push(builder.sub_extension(cubing_input, cubing_input_wire));
let f = builder.cube_extension(cubing_input_wire);
addition_buffer = builder.add_extension(addition_buffer, f);
state[active] = builder.sub_extension(state[active], f);
}
for i in 0..W {
state[i] = builder.add_extension(state[i], addition_buffer);
constraints
.push(builder.sub_extension(state[i], vars.local_wires[Self::wire_output(i)]));
}
constraints
}
fn generators(
&self,
gate_index: usize,
_local_constants: &[F],
) -> Vec<Box<dyn WitnessGenerator<F>>> {
let gen = GMiMCGenerator {
gate_index,
constants: self.constants.clone(),
};
vec![Box::new(gen)]
}
fn num_wires(&self) -> usize {
Self::end()
}
fn num_constants(&self) -> usize {
0
}
fn degree(&self) -> usize {
3
}
fn num_constraints(&self) -> usize {
R + W + 1
}
}
#[derive(Debug)]
struct GMiMCGenerator<F: Extendable<D>, const D: usize, const R: usize> {
gate_index: usize,
constants: Arc<[F; R]>,
}
impl<F: Extendable<D>, const D: usize, const R: usize> SimpleGenerator<F>
for GMiMCGenerator<F, D, R>
{
fn dependencies(&self) -> Vec<Target> {
let mut dep_input_indices = Vec::with_capacity(W + 1);
for i in 0..W {
dep_input_indices.push(GMiMCGate::<F, D, R>::wire_input(i));
}
dep_input_indices.push(GMiMCGate::<F, D, R>::WIRE_SWAP);
dep_input_indices
.into_iter()
.map(|input| {
Target::Wire(Wire {
gate: self.gate_index,
input,
})
})
.collect()
}
fn run_once(&self, witness: &PartialWitness<F>, out_buffer: &mut GeneratedValues<F>) {
let mut state = (0..W)
.map(|i| {
witness.get_wire(Wire {
gate: self.gate_index,
input: GMiMCGate::<F, D, R>::wire_input(i),
})
})
.collect::<Vec<_>>();
let swap_value = witness.get_wire(Wire {
gate: self.gate_index,
input: GMiMCGate::<F, D, R>::WIRE_SWAP,
});
debug_assert!(swap_value == F::ZERO || swap_value == F::ONE);
if swap_value == F::ONE {
for i in 0..4 {
state.swap(i, 4 + i);
}
}
// Value that is implicitly added to each element.
// See https://affine.group/2020/02/starkware-challenge
let mut addition_buffer = F::ZERO;
for r in 0..R {
let active = r % W;
let cubing_input = state[active] + addition_buffer + self.constants[r];
out_buffer.set_wire(
Wire {
gate: self.gate_index,
input: GMiMCGate::<F, D, R>::wire_cubing_input(r),
},
cubing_input,
);
let f = cubing_input.cube();
addition_buffer += f;
state[active] -= f;
}
for i in 0..W {
state[i] += addition_buffer;
out_buffer.set_wire(
Wire {
gate: self.gate_index,
input: GMiMCGate::<F, D, R>::wire_output(i),
},
state[i],
);
}
}
}
#[cfg(test)]
mod tests {
use std::convert::TryInto;
use std::sync::Arc;
use anyhow::Result;
use crate::field::crandall_field::CrandallField;
use crate::field::field_types::Field;
use crate::gates::gate::Gate;
use crate::gates::gate_testing::{test_eval_fns, test_low_degree};
use crate::gates::gmimc::{GMiMCGate, W};
use crate::hash::gmimc::gmimc_permute_naive;
use crate::iop::generator::generate_partial_witness;
use crate::iop::wire::Wire;
use crate::iop::witness::PartialWitness;
use crate::util::timing::TimingTree;
#[test]
fn generated_output() {
type F = CrandallField;
const R: usize = 101;
let constants = Arc::new([F::TWO; R]);
type Gate = GMiMCGate<F, 4, R>;
let gate = Gate::new(constants.clone());
let permutation_inputs = (0..W).map(F::from_canonical_usize).collect::<Vec<_>>();
let mut witness = PartialWitness::new(1 << 14, 126, 1000);
witness.set_wire(
Wire {
gate: 0,
input: Gate::WIRE_SWAP,
},
F::ZERO,
);
for i in 0..W {
witness.set_wire(
Wire {
gate: 0,
input: Gate::wire_input(i),
},
permutation_inputs[i],
);
}
let generators = gate.generators(0, &[]);
generate_partial_witness(
&mut witness,
&generators,
130,
100,
100,
&mut TimingTree::default(),
);
let expected_outputs: [F; W] =
gmimc_permute_naive(permutation_inputs.try_into().unwrap(), constants);
for i in 0..W {
let out = witness.get_wire(Wire {
gate: 0,
input: Gate::wire_output(i),
});
assert_eq!(out, expected_outputs[i]);
}
}
#[test]
fn low_degree() {
type F = CrandallField;
const R: usize = 101;
let constants = Arc::new([F::TWO; R]);
let gate = GMiMCGate::<F, 4, R>::new(constants);
test_low_degree(gate)
}
#[test]
fn eval_fns() -> Result<()> {
type F = CrandallField;
const R: usize = 101;
let constants = Arc::new([F::TWO; R]);
let gate = GMiMCGate::<F, 4, R>::new(constants);
test_eval_fns(gate)
}
}