frost/secp256k1-zkp
3
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Avoid division when decomposing scalars

Browse Source 
- In secp256k1_gej_split_exp, there are two divisions used. Since the denominator is a constant known at compile-time, each can be replaced by a multiplication followed by a right-shift (and rounding).
- Add the constants g1, g2 for this purpose and rewrite secp256k1_scalar_split_lambda_var accordingly.
- Remove secp256k1_num_div since no longer used

Rebased-by: Pieter Wuille
This commit is contained in:
Peter Dettman
2014-11-15 23:04:02 +07:00
committed by Pieter Wuille
parent ff8746d457
commit cc604e9842
4 changed files with 50 additions and 40 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
src/num_gmp_impl.h
View File

@@ -206,25 +206,6 @@ static void secp256k1_num_mul(secp256k1_num_t *r, const secp256k1_num_t *a, cons
memset(tmp, 0, sizeof(tmp));
}
static void secp256k1_num_div(secp256k1_num_t *r, const secp256k1_num_t *a, const secp256k1_num_t *b) {
secp256k1_num_sanity(a);
secp256k1_num_sanity(b);
if (b->limbs > a->limbs) {
r->limbs = 1;
r->data[0] = 0;
r->neg = 0;
return;
}
mp_limb_t quo[2*NUM_LIMBS+1];
mp_limb_t rem[2*NUM_LIMBS+1];
mpn_tdiv_qr(quo, rem, 0, a->data, a->limbs, b->data, b->limbs);
mpn_copyi(r->data, quo, a->limbs - b->limbs + 1);
r->limbs = a->limbs - b->limbs + 1;
while (r->limbs > 1 && r->data[r->limbs - 1]==0) r->limbs--;
r->neg = a->neg ^ b->neg;
}
static void secp256k1_num_shift(secp256k1_num_t *r, int bits) {
if (bits % GMP_NUMB_BITS) {
// Shift within limbs.