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Remove point-at-infinity filter in g1_lincomb_fast #588

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Merged
asn-d6 merged 1 commit into from
Aug 1, 2025
+3 −26
Merged

Remove point-at-infinity filter in g1_lincomb_fast #588

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29 changes: 3 additions & 26 deletions src/common/lincomb.c
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,6 @@ void g1_lincomb_naive(g1_t *out, const g1_t *p, const fr_t *coeffs, size_t len)
C_KZG_RET g1_lincomb_fast(g1_t *out, const g1_t *p, const fr_t *coeffs, size_t len) {
C_KZG_RET ret;
limb_t *scratch = NULL;
blst_p1 *p_filtered = NULL;
blst_p1_affine *p_affine = NULL;
blst_scalar *scalars = NULL;

Expand All @@ -83,8 +82,6 @@ C_KZG_RET g1_lincomb_fast(g1_t *out, const g1_t *p, const fr_t *coeffs, size_t l
}

/* Allocate space for arrays */
ret = c_kzg_calloc((void **)&p_filtered, len, sizeof(blst_p1));
if (ret != C_KZG_OK) goto out;
ret = c_kzg_calloc((void **)&p_affine, len, sizeof(blst_p1_affine));
if (ret != C_KZG_OK) goto out;
ret = c_kzg_calloc((void **)&scalars, len, sizeof(blst_scalar));
Expand All @@ -100,38 +97,18 @@ C_KZG_RET g1_lincomb_fast(g1_t *out, const g1_t *p, const fr_t *coeffs, size_t l
blst_scalar_from_fr(&scalars[i], &coeffs[i]);
}

/* Filter out zero points: make a new list p_filtered that contains only non-zero points */
size_t new_len = 0;
for (size_t i = 0; i < len; i++) {
if (!blst_p1_is_inf(&p[i])) {
/* Copy valid points to the new position */
p_filtered[new_len] = p[i];
scalars[new_len] = scalars[i];
new_len++;
}
}

/* Check if the new length is fine */
if (new_len < min_length_threshold) {
/* We must use the original inputs */
g1_lincomb_naive(out, p, coeffs, len);
ret = C_KZG_OK;
goto out;
}

/* Transform the points to affine representation */
const blst_p1 *p_arg[2] = {p_filtered, NULL};
blst_p1s_to_affine(p_affine, p_arg, new_len);
const blst_p1 *p_arg[2] = {p, NULL};
blst_p1s_to_affine(p_affine, p_arg, len);

/* Call the Pippenger implementation */
const byte *scalars_arg[2] = {(byte *)scalars, NULL};
const blst_p1_affine *points_arg[2] = {p_affine, NULL};
blst_p1s_mult_pippenger(out, points_arg, new_len, scalars_arg, BITS_PER_FIELD_ELEMENT, scratch);
blst_p1s_mult_pippenger(out, points_arg, len, scalars_arg, BITS_PER_FIELD_ELEMENT, scratch);
ret = C_KZG_OK;

out:
c_kzg_free(scratch);
c_kzg_free(p_filtered);
c_kzg_free(p_affine);
c_kzg_free(scalars);
return ret;
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