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c-kzg-4844
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Use batch inversion for Lagrange commitment

This commit is contained in:
Dankrad Feist 2022-09-17 23:25:21 +01:00
parent a2a4e57622
commit 80b256ad5f
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GPG Key ID: 6815E6A20BEBBABA
1 changed files with 21 additions and 5 deletions
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26
src/kzg_proofs.c
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@ -97,6 +97,13 @@ C_KZG_RET compute_proof_single_l(g1_t *out, const poly_l *p, const fr_t *x0, con
uint64_t i, m = 0;
new_poly_l(&q, p->length);
fr_t *inverses_in, *inverses;
TRY(new_fr_array(&inverses_in, p->length));
TRY(new_fr_array(&inverses, p->length));
for (i = 0; i < q.length; i++) {
if (fr_equal(x0, &ks->fs->expanded_roots_of_unity[i])) {
m = i + 1;
@ -104,23 +111,32 @@ C_KZG_RET compute_proof_single_l(g1_t *out, const poly_l *p, const fr_t *x0, con
}
// (p_i - y) / (ω_i - x0)
fr_sub(&q.values[i], &p->values[i], y);
fr_sub(&tmp, &ks->fs->expanded_roots_of_unity[i], x0);
fr_div(&q.values[i], &q.values[i], &tmp);
fr_sub(&inverses_in[i], &ks->fs->expanded_roots_of_unity[i], x0);
}
TRY(fr_batch_inv(inverses, inverses_in, q.length));
for (i = 0; i < q.length; i++) {
fr_mul(&q.values[i], &q.values[i], &inverses[i]);
}
if (m) { // ω_m == x0
q.values[--m] = fr_zero;
for (i=0; i < q.length; i++) {
if (i == m) continue;
// (p_i - y) * ω_i / (x0 * (x0 - ω_i))
fr_sub(&tmp, x0, &ks->fs->expanded_roots_of_unity[i]);
fr_mul(&tmp, &tmp, x0);
fr_mul(&inverses_in[i], &tmp, x0);
}
TRY(fr_batch_inv(inverses, inverses_in, q.length));
for (i=0; i < q.length; i++) {
fr_sub(&tmp2, &p->values[i], y);
fr_div(&tmp, &tmp2, &tmp);
fr_mul(&tmp, &tmp2, &inverses[i]);
fr_mul(&tmp, &tmp, &ks->fs->expanded_roots_of_unity[i]);
fr_add(&q.values[m], &q.values[m], &tmp);
}
}
free(inverses_in);
free(inverses);
return commit_to_poly_l(out, &q, ks);
}