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c-kzg-4844
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Optimized eval_poly_l with batch inversion

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Dankrad Feist 2022-09-17 18:00:54 +01:00
parent 4c8787d87b
commit dcf68949b3
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GPG Key ID: 6815E6A20BEBBABA
3 changed files with 23 additions and 9 deletions
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2
src/c_kzg.h
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@ -92,7 +92,7 @@ typedef struct {
} poly_l; // Lagrange form
void eval_poly(fr_t *out, const poly *p, const fr_t *x);
void eval_poly_l(fr_t *out, const poly_l *p, const fr_t *x, const FFTSettings *fs);
C_KZG_RET eval_poly_l(fr_t *out, const poly_l *p, const fr_t *x, const FFTSettings *fs);
C_KZG_RET poly_inverse(poly *out, poly *b);
C_KZG_RET poly_mul(poly *out, const poly *a, const poly *b);
C_KZG_RET poly_mul_(poly *out, const poly *a, const poly *b, FFTSettings *fs);

29
src/poly.c
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@ -102,21 +102,32 @@ void eval_poly(fr_t *out, const poly *p, const fr_t *x) {
}
}
// TODO: optimize via batch inversion
void eval_poly_l(fr_t *out, const poly_l *p, const fr_t *x, const FFTSettings *fs) {
fr_t tmp;
/**
* Evaluate a polynomial in Lagrange formover the finite field at a point.
*
* @param[out] out The value of the polynomial at the point @p x
* @param[in] p The polynomial in Lagrange form
* @param[in] x The x-coordinate to be evaluated
*/
C_KZG_RET eval_poly_l(fr_t *out, const poly_l *p, const fr_t *x, const FFTSettings *fs) {
fr_t tmp, *inverses_in, *inverses;
uint64_t i;
const uint64_t stride = fs->max_width / p->length;
*out = fr_zero;
TRY(new_fr_array(&inverses_in, p->length));
TRY(new_fr_array(&inverses, p->length));
for (i = 0; i < p->length; i++) {
if (fr_equal(x, &fs->expanded_roots_of_unity[i * stride])) {
*out = p->values[i];
return;
return C_KZG_OK;
}
fr_sub(&tmp, x, &fs->expanded_roots_of_unity[i * stride]);
fr_inv(&tmp, &tmp);
fr_mul(&tmp, &tmp, &fs->expanded_roots_of_unity[i * stride]);
fr_sub(&inverses_in[i], x, &fs->expanded_roots_of_unity[i * stride]);
}
TRY(fr_batch_inv(inverses, inverses_in, p->length));
*out = fr_zero;
for (i = 0; i < p->length; i++) {
fr_mul(&tmp, &inverses[i], &fs->expanded_roots_of_unity[i * stride]);
fr_mul(&tmp, &tmp, &p->values[i]);
fr_add(out, out, &tmp);
}
@ -125,6 +136,8 @@ void eval_poly_l(fr_t *out, const poly_l *p, const fr_t *x, const FFTSettings *f
fr_pow(&tmp, x, p->length);
fr_sub(&tmp, &tmp, &fr_one);
fr_mul(out, out, &tmp);
return C_KZG_OK;
}
/**

1
src/utility.h
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@ -49,3 +49,4 @@ uint64_t next_power_of_two(uint64_t v);
uint32_t reverse_bits(uint32_t a);
uint32_t reverse_bits_limited(uint32_t n, uint32_t value);
C_KZG_RET reverse_bit_order(void *values, size_t size, uint64_t n);
C_KZG_RET fr_batch_inv(fr_t *out, const fr_t *a, size_t len);