From 4c950bbeafb4cbbeb5ffc742a29e916224fbcb4e Mon Sep 17 00:00:00 2001 From: Peter Dettman Date: Fri, 1 Dec 2017 02:52:19 +0700 Subject: [PATCH] Save some additions per window in _pippenger_wnaf --- src/ecmult_impl.h | 40 ++++++++++++++++++++-------------------- 1 file changed, 20 insertions(+), 20 deletions(-) diff --git a/src/ecmult_impl.h b/src/ecmult_impl.h index 3749cf9..67fd4c6 100644 --- a/src/ecmult_impl.h +++ b/src/ecmult_impl.h @@ -654,14 +654,10 @@ static int secp256k1_ecmult_pippenger_wnaf(secp256k1_gej *buckets, int bucket_wi for (i = n_wnaf - 1; i >= 0; i--) { secp256k1_gej running_sum; - secp256k1_gej walking_sum; for(j = 0; j < ECMULT_TABLE_SIZE(bucket_window+2); j++) { secp256k1_gej_set_infinity(&buckets[j]); } - for(j = 0; j < bucket_window+1; j++) { - secp256k1_gej_double_var(r, r, NULL); - } for (np = 0; np < no; ++np) { int n = state->wnaf_na[np*n_wnaf + i]; @@ -688,24 +684,28 @@ static int secp256k1_ecmult_pippenger_wnaf(secp256k1_gej *buckets, int bucket_wi secp256k1_gej_add_ge_var(&buckets[idx], &buckets[idx], &tmp, NULL); } } - secp256k1_gej_set_infinity(&running_sum); - secp256k1_gej_set_infinity(&walking_sum); - /* Compute walking_sum as bucket[0] + 3*bucket[1] + 5*bucket[2] + ... - * by first setting - * running_sum = bucket[0] + bucket[1] + bucket[2] + ... - * walking_sum = bucket[0] + 2*bucket[1] + 3*bucket[2] + ... - * and then computing - * walking_sum = 2*walking_sum - running_sum - */ - for(j = ECMULT_TABLE_SIZE(bucket_window+2) - 1; j >= 0; j--) { - secp256k1_gej_add_var(&running_sum, &running_sum, &buckets[j], NULL); - secp256k1_gej_add_var(&walking_sum, &walking_sum, &running_sum, NULL); + + for(j = 0; j < bucket_window; j++) { + secp256k1_gej_double_var(r, r, NULL); } - secp256k1_gej_double_var(&walking_sum, &walking_sum, NULL); - secp256k1_gej_neg(&running_sum, &running_sum); - secp256k1_gej_add_var(&walking_sum, &walking_sum, &running_sum, NULL); - secp256k1_gej_add_var(r, r, &walking_sum, NULL); + secp256k1_gej_set_infinity(&running_sum); + /* Accumulate the sum: bucket[0] + 3*bucket[1] + 5*bucket[2] + 7*bucket[3] + ... + * = bucket[0] + bucket[1] + bucket[2] + bucket[3] + ... + * + 2 * (bucket[1] + 2*bucket[2] + 3*bucket[3] + ...) + * using an intermediate running sum: + * running_sum = bucket[0] + bucket[1] + bucket[2] + ... + * + * The doubling is done implicitly by deferring the final window doubling (of 'r'). + */ + for(j = ECMULT_TABLE_SIZE(bucket_window+2) - 1; j > 0; j--) { + secp256k1_gej_add_var(&running_sum, &running_sum, &buckets[j], NULL); + secp256k1_gej_add_var(r, r, &running_sum, NULL); + } + + secp256k1_gej_add_var(&running_sum, &running_sum, &buckets[0], NULL); + secp256k1_gej_double_var(r, r, NULL); + secp256k1_gej_add_var(r, r, &running_sum, NULL); } return 1; }