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use crate::bit_iterator::*;
use crate::constraint_system::StandardComposer;
use crate::constraint_system::{Variable, WireData};
use dusk_bls12_381::Scalar;
impl StandardComposer {
fn logic_gate(
&mut self,
a: Variable,
b: Variable,
num_bits: usize,
is_xor_gate: bool,
) -> Variable {
assert_eq!(num_bits & 1, 0);
let num_quads = num_bits >> 1;
let mut left_accumulator = Scalar::zero();
let mut right_accumulator = Scalar::zero();
let mut out_accumulator = Scalar::zero();
let mut left_quad: u8;
let mut right_quad: u8;
let a_bit_iter = BitIterator8::new(self.variables[&a].to_bytes());
let a_bits: Vec<_> = a_bit_iter.skip(256 - num_bits).collect();
let b_bit_iter = BitIterator8::new(self.variables[&b].to_bytes());
let b_bits: Vec<_> = b_bit_iter.skip(256 - num_bits).collect();
assert!(a_bits.len() >= num_bits);
assert!(b_bits.len() >= num_bits);
self.perm
.add_variable_to_map(self.zero_var, WireData::Left(self.n));
self.perm
.add_variable_to_map(self.zero_var, WireData::Right(self.n));
self.perm
.add_variable_to_map(self.zero_var, WireData::Fourth(self.n));
self.w_l.push(self.zero_var);
self.w_r.push(self.zero_var);
self.w_4.push(self.zero_var);
self.n += 1;
for i in 0..num_quads {
left_quad = {
let idx = i << 1;
((a_bits[idx] as u8) << 1) + (a_bits[idx + 1] as u8)
};
right_quad = {
let idx = i << 1;
((b_bits[idx] as u8) << 1) + (b_bits[idx + 1] as u8)
};
let left_quad_fr = Scalar::from(left_quad as u64);
let right_quad_fr = Scalar::from(right_quad as u64);
let out_quad_fr = match is_xor_gate {
true => Scalar::from((left_quad ^ right_quad) as u64),
false => Scalar::from((left_quad & right_quad) as u64),
};
let prod_quad_fr = Scalar::from((left_quad * right_quad) as u64);
let prev_left_accum = left_accumulator;
let prev_right_accum = right_accumulator;
let prev_out_accum = out_accumulator;
left_accumulator *= Scalar::from(4u64);
left_accumulator += left_quad_fr;
right_accumulator *= Scalar::from(4u64);
right_accumulator += right_quad_fr;
out_accumulator *= Scalar::from(4u64);
out_accumulator += out_quad_fr;
assert!(left_accumulator - (prev_left_accum * Scalar::from(4u64)) < Scalar::from(4u64));
assert!(
right_accumulator - (prev_right_accum * Scalar::from(4u64)) < Scalar::from(4u64)
);
assert!(out_accumulator - (prev_out_accum * Scalar::from(4u64)) < Scalar::from(4u64));
let var_a = self.add_input(left_accumulator);
let var_b = self.add_input(right_accumulator);
let var_c = match i == num_quads {
true => self.zero_var,
false => self.add_input(prod_quad_fr),
};
let var_4 = self.add_input(out_accumulator);
self.perm.add_variable_to_map(var_a, WireData::Left(self.n));
self.perm
.add_variable_to_map(var_b, WireData::Right(self.n));
self.perm
.add_variable_to_map(var_4, WireData::Fourth(self.n));
self.perm
.add_variable_to_map(var_c, WireData::Output(self.n - 1));
self.w_l.push(var_a);
self.w_r.push(var_b);
self.w_o.push(var_c);
self.w_4.push(var_4);
self.n += 1;
}
self.perm
.add_variable_to_map(self.zero_var, WireData::Output(self.n - 1));
self.w_o.push(self.zero_var);
for _ in 0..num_quads {
self.q_m.push(Scalar::zero());
self.q_l.push(Scalar::zero());
self.q_r.push(Scalar::zero());
self.q_arith.push(Scalar::zero());
self.q_o.push(Scalar::zero());
self.q_4.push(Scalar::zero());
self.q_range.push(Scalar::zero());
self.q_ecc.push(Scalar::zero());
match is_xor_gate {
true => {
self.q_c.push(-Scalar::one());
self.q_logic.push(-Scalar::one());
}
false => {
self.q_c.push(Scalar::one());
self.q_logic.push(Scalar::one());
}
};
}
self.q_m.push(Scalar::zero());
self.q_l.push(Scalar::zero());
self.q_r.push(Scalar::zero());
self.q_arith.push(Scalar::zero());
self.q_o.push(Scalar::zero());
self.q_4.push(Scalar::zero());
self.q_range.push(Scalar::zero());
self.q_ecc.push(Scalar::zero());
self.q_c.push(Scalar::zero());
self.q_logic.push(Scalar::zero());
let zeros = vec![Scalar::zero(); num_quads + 1];
self.public_inputs.extend(zeros.iter());
assert_eq!(
self.variables[&a]
& (Scalar::from(2u64).pow(&[(num_bits) as u64, 0, 0, 0]) - Scalar::one()),
self.variables[&self.w_l[self.n - 1]]
);
assert_eq!(
self.variables[&b]
& (Scalar::from(2u64).pow(&[(num_bits) as u64, 0, 0, 0]) - Scalar::one()),
self.variables[&self.w_r[self.n - 1]]
);
self.w_4[self.w_4.len() - 1]
}
pub fn xor_gate(&mut self, a: Variable, b: Variable, num_bits: usize) -> Variable {
self.logic_gate(a, b, num_bits, true)
}
pub fn and_gate(&mut self, a: Variable, b: Variable, num_bits: usize) -> Variable {
self.logic_gate(a, b, num_bits, false)
}
}
#[cfg(test)]
mod tests {
use super::super::helper::*;
use dusk_bls12_381::Scalar;
#[test]
fn test_logic_xor_and_constraint() {
let res = gadget_tester(
|composer| {
let witness_a = composer.add_input(Scalar::from(500u64));
let witness_b = composer.add_input(Scalar::from(357u64));
let xor_res = composer.xor_gate(witness_a, witness_b, 10);
composer.constrain_to_constant(
xor_res,
Scalar::from(500u64 ^ 357u64),
Scalar::zero(),
);
},
200,
);
assert!(res.is_ok());
let res = gadget_tester(
|composer| {
let witness_a = composer.add_input(Scalar::from(469u64));
let witness_b = composer.add_input(Scalar::from(321u64));
let xor_res = composer.and_gate(witness_a, witness_b, 10);
composer.constrain_to_constant(
xor_res,
Scalar::from(469u64 & 321u64),
Scalar::zero(),
);
},
200,
);
assert!(res.is_ok());
let res = gadget_tester(
|composer| {
let witness_a = composer.add_input(Scalar::from(139u64));
let witness_b = composer.add_input(Scalar::from(33u64));
let xor_res = composer.xor_gate(witness_a, witness_b, 10);
composer.constrain_to_constant(
xor_res,
Scalar::from(139u64 & 33u64),
Scalar::zero(),
);
},
200,
);
assert!(res.is_err());
let res = gadget_tester(
|composer| {
let witness_a = composer.add_input(Scalar::from(256u64));
let witness_b = composer.add_input(Scalar::from(235u64));
let xor_res = composer.xor_gate(witness_a, witness_b, 2);
composer.constrain_to_constant(xor_res, Scalar::from(256 ^ 235), Scalar::zero());
},
200,
);
assert!(res.is_err());
}
#[test]
#[should_panic]
fn test_logical_gate_odd_bit_num() {
let _ = gadget_tester(
|composer| {
let witness_a = composer.add_input(Scalar::from(500u64));
let witness_b = composer.add_input(Scalar::from(499u64));
let xor_res = composer.xor_gate(witness_a, witness_b, 9);
composer.constrain_to_constant(xor_res, Scalar::from(7u64), Scalar::zero());
},
200,
);
}
}