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Save some additions per window in _pippenger_wnaf

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Peter Dettman 2017-12-01 02:52:19 +07:00 committed by Jonas Nick
parent a58f543f5a
commit 4c950bbeaf
1 changed files with 20 additions and 20 deletions
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40
src/ecmult_impl.h
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@ -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;
}