use alloc::boxed::Box;
use alloc::string::String;
use alloc::vec::Vec;
use alloc::{format, vec};
use core::marker::PhantomData;
use crate::field::extension::Extendable;
use crate::field::ops::Square;
use crate::field::packed::PackedField;
use crate::field::types::Field;
use crate::gates::gate::Gate;
use crate::gates::packed_util::PackedEvaluableBase;
use crate::gates::util::StridedConstraintConsumer;
use crate::hash::hash_types::RichField;
use crate::iop::ext_target::ExtensionTarget;
use crate::iop::generator::{GeneratedValues, SimpleGenerator, WitnessGenerator};
use crate::iop::target::Target;
use crate::iop::wire::Wire;
use crate::iop::witness::{PartitionWitness, Witness, WitnessWrite};
use crate::plonk::circuit_builder::CircuitBuilder;
use crate::plonk::circuit_data::CircuitConfig;
use crate::plonk::vars::{
EvaluationTargets, EvaluationVars, EvaluationVarsBase, EvaluationVarsBaseBatch,
EvaluationVarsBasePacked,
};
#[derive(Clone, Debug)]
pub struct ExponentiationGate<F: RichField + Extendable<D>, const D: usize> {
pub num_power_bits: usize,
pub _phantom: PhantomData<F>,
}
impl<F: RichField + Extendable<D>, const D: usize> ExponentiationGate<F, D> {
pub fn new(num_power_bits: usize) -> Self {
Self {
num_power_bits,
_phantom: PhantomData,
}
}
pub fn new_from_config(config: &CircuitConfig) -> Self {
let num_power_bits = Self::max_power_bits(config.num_wires, config.num_routed_wires);
Self::new(num_power_bits)
}
fn max_power_bits(num_wires: usize, num_routed_wires: usize) -> usize {
let max_for_routed_wires = num_routed_wires - 2;
let max_for_wires = (num_wires - 2) / 2;
max_for_routed_wires.min(max_for_wires)
}
pub fn wire_base(&self) -> usize {
0
}
pub fn wire_power_bit(&self, i: usize) -> usize {
debug_assert!(i < self.num_power_bits);
1 + i
}
pub fn wire_output(&self) -> usize {
1 + self.num_power_bits
}
pub fn wire_intermediate_value(&self, i: usize) -> usize {
debug_assert!(i < self.num_power_bits);
2 + self.num_power_bits + i
}
}
impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for ExponentiationGate<F, D> {
fn id(&self) -> String {
format!("{self:?}<D={D}>")
}
fn eval_unfiltered(&self, vars: EvaluationVars<F, D>) -> Vec<F::Extension> {
let base = vars.local_wires[self.wire_base()];
let power_bits: Vec<_> = (0..self.num_power_bits)
.map(|i| vars.local_wires[self.wire_power_bit(i)])
.collect();
let intermediate_values: Vec<_> = (0..self.num_power_bits)
.map(|i| vars.local_wires[self.wire_intermediate_value(i)])
.collect();
let output = vars.local_wires[self.wire_output()];
let mut constraints = Vec::with_capacity(self.num_constraints());
for i in 0..self.num_power_bits {
let prev_intermediate_value = if i == 0 {
F::Extension::ONE
} else {
intermediate_values[i - 1].square()
};
let cur_bit = power_bits[self.num_power_bits - i - 1];
let not_cur_bit = F::Extension::ONE - cur_bit;
let computed_intermediate_value =
prev_intermediate_value * (cur_bit * base + not_cur_bit);
constraints.push(computed_intermediate_value - intermediate_values[i]);
}
constraints.push(output - intermediate_values[self.num_power_bits - 1]);
constraints
}
fn eval_unfiltered_base_one(
&self,
_vars: EvaluationVarsBase<F>,
_yield_constr: StridedConstraintConsumer<F>,
) {
panic!("use eval_unfiltered_base_packed instead");
}
fn eval_unfiltered_base_batch(&self, vars_base: EvaluationVarsBaseBatch<F>) -> Vec<F> {
self.eval_unfiltered_base_batch_packed(vars_base)
}
fn eval_unfiltered_circuit(
&self,
builder: &mut CircuitBuilder<F, D>,
vars: EvaluationTargets<D>,
) -> Vec<ExtensionTarget<D>> {
let base = vars.local_wires[self.wire_base()];
let power_bits: Vec<_> = (0..self.num_power_bits)
.map(|i| vars.local_wires[self.wire_power_bit(i)])
.collect();
let intermediate_values: Vec<_> = (0..self.num_power_bits)
.map(|i| vars.local_wires[self.wire_intermediate_value(i)])
.collect();
let output = vars.local_wires[self.wire_output()];
let mut constraints = Vec::with_capacity(self.num_constraints());
let one = builder.one_extension();
for i in 0..self.num_power_bits {
let prev_intermediate_value = if i == 0 {
one
} else {
builder.square_extension(intermediate_values[i - 1])
};
let cur_bit = power_bits[self.num_power_bits - i - 1];
let mul_by = builder.select_ext_generalized(cur_bit, base, one);
let intermediate_value_diff =
builder.mul_sub_extension(prev_intermediate_value, mul_by, intermediate_values[i]);
constraints.push(intermediate_value_diff);
}
let output_diff =
builder.sub_extension(output, intermediate_values[self.num_power_bits - 1]);
constraints.push(output_diff);
constraints
}
fn generators(&self, row: usize, _local_constants: &[F]) -> Vec<Box<dyn WitnessGenerator<F>>> {
let gen = ExponentiationGenerator::<F, D> {
row,
gate: self.clone(),
};
vec![Box::new(gen.adapter())]
}
fn num_wires(&self) -> usize {
self.wire_intermediate_value(self.num_power_bits - 1) + 1
}
fn num_constants(&self) -> usize {
0
}
fn degree(&self) -> usize {
4
}
fn num_constraints(&self) -> usize {
self.num_power_bits + 1
}
}
impl<F: RichField + Extendable<D>, const D: usize> PackedEvaluableBase<F, D>
for ExponentiationGate<F, D>
{
fn eval_unfiltered_base_packed<P: PackedField<Scalar = F>>(
&self,
vars: EvaluationVarsBasePacked<P>,
mut yield_constr: StridedConstraintConsumer<P>,
) {
let base = vars.local_wires[self.wire_base()];
let power_bits: Vec<_> = (0..self.num_power_bits)
.map(|i| vars.local_wires[self.wire_power_bit(i)])
.collect();
let intermediate_values: Vec<_> = (0..self.num_power_bits)
.map(|i| vars.local_wires[self.wire_intermediate_value(i)])
.collect();
let output = vars.local_wires[self.wire_output()];
for i in 0..self.num_power_bits {
let prev_intermediate_value = if i == 0 {
P::ONES
} else {
intermediate_values[i - 1].square()
};
let cur_bit = power_bits[self.num_power_bits - i - 1];
let not_cur_bit = P::ONES - cur_bit;
let computed_intermediate_value =
prev_intermediate_value * (cur_bit * base + not_cur_bit);
yield_constr.one(computed_intermediate_value - intermediate_values[i]);
}
yield_constr.one(output - intermediate_values[self.num_power_bits - 1]);
}
}
#[derive(Debug)]
struct ExponentiationGenerator<F: RichField + Extendable<D>, const D: usize> {
row: usize,
gate: ExponentiationGate<F, D>,
}
impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F>
for ExponentiationGenerator<F, D>
{
fn dependencies(&self) -> Vec<Target> {
let local_target = |column| Target::wire(self.row, column);
let mut deps = Vec::with_capacity(self.gate.num_power_bits + 1);
deps.push(local_target(self.gate.wire_base()));
for i in 0..self.gate.num_power_bits {
deps.push(local_target(self.gate.wire_power_bit(i)));
}
deps
}
fn run_once(&self, witness: &PartitionWitness<F>, out_buffer: &mut GeneratedValues<F>) {
let local_wire = |column| Wire {
row: self.row,
column,
};
let get_local_wire = |column| witness.get_wire(local_wire(column));
let num_power_bits = self.gate.num_power_bits;
let base = get_local_wire(self.gate.wire_base());
let power_bits = (0..num_power_bits)
.map(|i| get_local_wire(self.gate.wire_power_bit(i)))
.collect::<Vec<_>>();
let mut intermediate_values = Vec::new();
let mut current_intermediate_value = F::ONE;
for i in 0..num_power_bits {
if power_bits[num_power_bits - i - 1] == F::ONE {
current_intermediate_value *= base;
}
intermediate_values.push(current_intermediate_value);
current_intermediate_value *= current_intermediate_value;
}
for i in 0..num_power_bits {
let intermediate_value_wire = local_wire(self.gate.wire_intermediate_value(i));
out_buffer.set_wire(intermediate_value_wire, intermediate_values[i]);
}
let output_wire = local_wire(self.gate.wire_output());
out_buffer.set_wire(output_wire, intermediate_values[num_power_bits - 1]);
}
}
#[cfg(test)]
mod tests {
use anyhow::Result;
use rand::rngs::OsRng;
use rand::Rng;
use super::*;
use crate::field::goldilocks_field::GoldilocksField;
use crate::field::types::Sample;
use crate::gates::gate_testing::{test_eval_fns, test_low_degree};
use crate::hash::hash_types::HashOut;
use crate::plonk::config::{GenericConfig, PoseidonGoldilocksConfig};
use crate::util::log2_ceil;
const MAX_POWER_BITS: usize = 17;
#[test]
fn wire_indices() {
let gate = ExponentiationGate::<GoldilocksField, 4> {
num_power_bits: 5,
_phantom: PhantomData,
};
assert_eq!(gate.wire_base(), 0);
assert_eq!(gate.wire_power_bit(0), 1);
assert_eq!(gate.wire_power_bit(4), 5);
assert_eq!(gate.wire_output(), 6);
assert_eq!(gate.wire_intermediate_value(0), 7);
assert_eq!(gate.wire_intermediate_value(4), 11);
}
#[test]
fn low_degree() {
let config = CircuitConfig {
num_wires: 120,
num_routed_wires: 30,
..CircuitConfig::standard_recursion_config()
};
test_low_degree::<GoldilocksField, _, 4>(ExponentiationGate::new_from_config(&config));
}
#[test]
fn eval_fns() -> Result<()> {
const D: usize = 2;
type C = PoseidonGoldilocksConfig;
type F = <C as GenericConfig<D>>::F;
test_eval_fns::<F, C, _, D>(ExponentiationGate::new_from_config(
&CircuitConfig::standard_recursion_config(),
))
}
#[test]
fn test_gate_constraint() {
const D: usize = 2;
type C = PoseidonGoldilocksConfig;
type F = <C as GenericConfig<D>>::F;
type FF = <C as GenericConfig<D>>::FE;
fn get_wires(base: F, power: u64) -> Vec<FF> {
let mut power_bits = Vec::new();
let mut cur_power = power;
while cur_power > 0 {
power_bits.push(cur_power % 2);
cur_power /= 2;
}
let num_power_bits = power_bits.len();
let power_bits_f: Vec<_> = power_bits
.iter()
.map(|b| F::from_canonical_u64(*b))
.collect();
let mut v = vec![base];
v.extend(power_bits_f);
let mut intermediate_values = Vec::new();
let mut current_intermediate_value = F::ONE;
for i in 0..num_power_bits {
if power_bits[num_power_bits - i - 1] == 1 {
current_intermediate_value *= base;
}
intermediate_values.push(current_intermediate_value);
current_intermediate_value *= current_intermediate_value;
}
let output_value = intermediate_values[num_power_bits - 1];
v.push(output_value);
v.extend(intermediate_values);
v.iter().map(|&x| x.into()).collect::<Vec<_>>()
}
let mut rng = OsRng;
let base = F::TWO;
let power = rng.gen::<usize>() % (1 << MAX_POWER_BITS);
let num_power_bits = log2_ceil(power + 1);
let gate = ExponentiationGate::<F, D> {
num_power_bits,
_phantom: PhantomData,
};
let vars = EvaluationVars {
local_constants: &[],
local_wires: &get_wires(base, power as u64),
public_inputs_hash: &HashOut::rand(),
};
assert!(
gate.eval_unfiltered(vars).iter().all(|x| x.is_zero()),
"Gate constraints are not satisfied."
);
}
}