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feat: improve blob simulation speed #11075

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Jan 7, 2025
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feat: improve blob simulation speed #11075

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feat: improve blob simulation speed
TomAFrench Jan 6, 2025
4d2a2e5
Merge branch 'master' into tf/reduce-unnecessary-brillig
TomAFrench Jan 6, 2025
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TomAFrench Jan 7, 2025
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176 changes: 82 additions & 94 deletions noir-projects/noir-protocol-circuits/crates/blob/src/blob.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -227,67 +227,69 @@ fn barycentric_evaluate_blob_at_z(z: F, ys: [F; FIELDS_PER_BLOB]) -> F {
__compute_partial_sums(fracs, ROOTS)
};

// We split off the first term to check the initial sum

// partial_sums[0] <- (lhs[0] * rhs[0] + ... + lhs[7] * rhs[7])
// => (lhs[0] * rhs[0] + ... + lhs[7] * rhs[7]) - partial_sums[0] == 0
let lhs = [
[ROOTS[0]], [ROOTS[1]], [ROOTS[2]], [ROOTS[3]], [ROOTS[4]], [ROOTS[5]], [ROOTS[6]],
[ROOTS[7]],
];
let rhs = [
[fracs[0]], [fracs[1]], [fracs[2]], [fracs[3]], [fracs[4]], [fracs[5]], [fracs[6]],
[fracs[7]],
];
BigNum::evaluate_quadratic_expression(
lhs,
[[false], [false], [false], [false], [false], [false], [false], [false]],
rhs,
[[false], [false], [false], [false], [false], [false], [false], [false]],
[partial_sums[0]],
[true],
);
for i in 1..NUM_PARTIAL_SUMS {
// Seeking:
// ___i*8 - 1 ___i*8 + 7
// \ omega^i \ / y_k \
// sum_out = / y_i . --------- + / omega^k . | --------- |
// /____ z - omega^i /____ \ z - omega^k /
// 0 k = i*8
// ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// sum partial_sum
//
// ... that is:
//
// ___i*8 - 1 ___ 7
// \ omega^i \
// sum_out = / y_i . --------- + / lhs[j] . rhs[j]
// /____ z - omega^i /____
// 0 j = 0
// ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^
// sum partial_sum
//

let mut lhs: [[F; 1]; 8] = [std::mem::zeroed(); 8];
let mut rhs: [[F; 1]; 8] = [std::mem::zeroed(); 8];
for j in 0..8 {
let k = i * 8 + j;
lhs[j] = [ROOTS[k]]; // omega^k
rhs[j] = [fracs[k]]; // y_k / (z - omega^k)
}

let linear_terms = [partial_sums[i - 1], partial_sums[i]];

// partial_sums[i] <- partial_sums[i-1] + (lhs[8*i] * rhs[8*i] + ... + lhs[8*i + 7] * rhs[8*i + 7])
// => (lhs[8*i] * rhs[8*i] + ... + lhs[8*i + 7] * rhs[8*i + 7]) + partial_sums[i-1] - partial_sums[i] == 0
if !std::runtime::is_unconstrained() {
// We split off the first term to check the initial sum

// partial_sums[0] <- (lhs[0] * rhs[0] + ... + lhs[7] * rhs[7])
// => (lhs[0] * rhs[0] + ... + lhs[7] * rhs[7]) - partial_sums[0] == 0
let lhs = [
[ROOTS[0]], [ROOTS[1]], [ROOTS[2]], [ROOTS[3]], [ROOTS[4]], [ROOTS[5]], [ROOTS[6]],
[ROOTS[7]],
];
let rhs = [
[fracs[0]], [fracs[1]], [fracs[2]], [fracs[3]], [fracs[4]], [fracs[5]], [fracs[6]],
[fracs[7]],
];
BigNum::evaluate_quadratic_expression(
lhs,
[[false], [false], [false], [false], [false], [false], [false], [false]],
rhs,
[[false], [false], [false], [false], [false], [false], [false], [false]],
linear_terms,
[false, true],
[partial_sums[0]],
[true],
);
for i in 1..NUM_PARTIAL_SUMS {
// Seeking:
// ___i*8 - 1 ___i*8 + 7
// \ omega^i \ / y_k \
// sum_out = / y_i . --------- + / omega^k . | --------- |
// /____ z - omega^i /____ \ z - omega^k /
// 0 k = i*8
// ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// sum partial_sum
//
// ... that is:
//
// ___i*8 - 1 ___ 7
// \ omega^i \
// sum_out = / y_i . --------- + / lhs[j] . rhs[j]
// /____ z - omega^i /____
// 0 j = 0
// ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^
// sum partial_sum
//

// partial_sums[i] <- partial_sums[i-1] + (lhs[8*i] * rhs[8*i] + ... + lhs[8*i + 7] * rhs[8*i + 7])
// => (lhs[8*i] * rhs[8*i] + ... + lhs[8*i + 7] * rhs[8*i + 7]) + partial_sums[i-1] - partial_sums[i] == 0
let mut lhs: [[F; 1]; 8] = [std::mem::zeroed(); 8];
let mut rhs: [[F; 1]; 8] = [std::mem::zeroed(); 8];
for j in 0..8 {
let k = i * 8 + j;
lhs[j] = [ROOTS[k]]; // omega^k
rhs[j] = [fracs[k]]; // y_k / (z - omega^k)
}

let linear_terms = [partial_sums[i - 1], partial_sums[i]];

BigNum::evaluate_quadratic_expression(
lhs,
[[false], [false], [false], [false], [false], [false], [false], [false]],
rhs,
[[false], [false], [false], [false], [false], [false], [false], [false]],
linear_terms,
[false, true],
);
}
}

let factor = compute_factor(z);
Expand Down Expand Up @@ -317,14 +319,16 @@ fn compute_factor(z: F) -> F {

// (z_pow_d - one) * (D_INV) - factor = 0
// z_pow_d * D_INV - D_INV - factor = 0
BigNum::evaluate_quadratic_expression(
[[z_pow_d]],
[[false]],
[[D_INV]],
[[false]],
[factor, D_INV],
[true, true],
);
if !std::runtime::is_unconstrained() {
BigNum::evaluate_quadratic_expression(
[[z_pow_d]],
[[false]],
[[D_INV]],
[[false]],
[factor, D_INV],
[true, true],
);
}

// This version doesn't work:
// BigNum::evaluate_quadratic_expression(
Expand Down Expand Up @@ -371,17 +375,19 @@ fn compute_fracs(
__compute_fracs(z, ys, ROOTS)
};

for i in 0..FIELDS_PER_BLOB {
// frac <-- ys[i] / (z + neg_roots[i])
// frac * (z + neg_roots[i]) - ys[i] = 0
BigNum::evaluate_quadratic_expression(
[[fracs[i]]],
[[false]],
[[z, ROOTS[i].neg()]],
[[false, false]],
[ys[i]],
[true],
);
if !std::runtime::is_unconstrained() {
for i in 0..FIELDS_PER_BLOB {
// frac <-- ys[i] / (z + neg_roots[i])
// frac * (z + neg_roots[i]) - ys[i] = 0
BigNum::evaluate_quadratic_expression(
[[fracs[i]]],
[[false]],
[[z, ROOTS[i].neg()]],
[[false, false]],
[ys[i]],
[true],
);
}
}

fracs
Expand Down Expand Up @@ -442,7 +448,7 @@ mod tests {
field_to_bignum,
},
blob_public_inputs::BlobCommitment,
unconstrained_config::{D, D_INV, F, LOG_FIELDS_PER_BLOB},
unconstrained_config::{D, D_INV, F},
};
use bigint::{BigNum, fields::bls12_381Fr::BLS12_381_Fr_Params};
use types::{
Expand All @@ -451,24 +457,6 @@ mod tests {
tests::{fixture_builder::FixtureBuilder, utils::pad_end},
};

// Helper to return (z^d - 1)/d (unsafe - test only)
fn z_d_helper(challenge_z: F) -> F {
let mut t1 = unsafe { challenge_z.__mul(challenge_z) };
let mut t2: F = BigNum::new();
for _i in 0..LOG_FIELDS_PER_BLOB - 1 {
t2 = unsafe { t1.__mul(t1) };
t1 = t2;
}

let z_pow_d = t1;

let one: F = BigNum::one();

t1 = unsafe { z_pow_d.__sub(one) };
let factor = unsafe { t1.__mul(D_INV) };
factor
}

#[test]
unconstrained fn test_one_note() {
let mut tx_data = FixtureBuilder::new();
Expand Down Expand Up @@ -500,7 +488,7 @@ mod tests {
//* p(z).(z - 1) = ---------
//* d
//
let rhs = z_d_helper(challenge_z);
let rhs = super::compute_factor(challenge_z);
let z_minus_1 = unsafe { challenge_z.__sub(BigNum::one()) };
let lhs = y.__mul(z_minus_1);
assert_eq(lhs, rhs);
Expand Down
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