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Avoid division when decomposing scalars

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- 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
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2
src/ecmult_impl.h
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@@ -170,6 +170,8 @@ static void secp256k1_ecmult(secp256k1_gej_t *r, const secp256k1_gej_t *a, const
/* build wnaf representation for na_1 and na_lam. */
int wnaf_na_1[129]; int bits_na_1 = secp256k1_ecmult_wnaf(wnaf_na_1, &na_1, WINDOW_A);
int wnaf_na_lam[129]; int bits_na_lam = secp256k1_ecmult_wnaf(wnaf_na_lam, &na_lam, WINDOW_A);
VERIFY_CHECK(bits_na_1 <= 129);
VERIFY_CHECK(bits_na_lam <= 129);
int bits = bits_na_1;
if (bits_na_lam > bits) bits = bits_na_lam;
#else